JP3593968B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine.
[0002]
[Prior art]
BACKGROUND ART Exhaust gas from an internal combustion engine, particularly a diesel engine, contains harmful particulates containing carbon as a main component, and it is desired to reduce the amount of particulates discharged into the atmosphere. Therefore, it has been proposed to arrange a particulate filter as a filter for collecting particulates in an exhaust system of a diesel engine. Such a particulate filter has a large exhaust resistance with an increase in the amount of trapped particulates. Therefore, it is necessary to burn the collected particulates and regenerate the particulate filter itself.
[0003]
If the exhaust gas is heated to a high temperature as in the case of high-load high-speed operation of the engine, the particulates spontaneously ignite and burn, so that the particulate filter can be regenerated. However, there is no guarantee that such an engine high-load high-speed operation is frequently performed, and in general, a heater or an oxidation catalyst is disposed in a particulate filter, and at the time of regeneration, the heater is operated, or A regeneration process such as supplying unburned fuel or the like to the oxidation catalyst is performed.
[0004]
Therefore, it is necessary to determine the regeneration time of the particulate filter. However, if the determined regeneration time is too early, the regeneration process will be performed unnecessarily, resulting in a large battery or a large amount of fuel consumption. Problems arise. On the other hand, if the determined regeneration time is too late, the exhaust resistance of the engine exhaust system becomes very large, and the engine output decreases.
[0005]
Thus, it is desired to accurately determine the regeneration time of the particulate filter. For example, it has been proposed to determine the regeneration time based on the increase in the amount of particulate collection as the vehicle traveling distance increases. However, the amount of particulate collection increases depending on the driving state during a predetermined traveling distance. Because of the differences, this method cannot determine the exact playback time.
[0006]
In addition, pressure sensors are arranged on the upstream and downstream sides of the particulate filter, and the regeneration timing is set based on the fact that the differential pressure detected by these two pressure sensors increases as the particulate collection amount increases. Judgment has also been proposed, but the pressure sensor is expensive and the pressure sensor itself has relatively large measurement errors, which is also less preferred.
[0007]
In order to judge the regeneration time of the particulate filter at a low cost and relatively accurately, Japanese Patent Laid-Open Publication No. 3-41112 discloses that the measurement is performed based on the fact that the intake fresh air amount decreases as the particulate collection amount increases. It has been proposed to determine the regeneration time of the particulate filter by comparing the intake fresh air amount and a reference value for each engine operating state.
[0008]
In the determination of the regeneration time of the particulate filter based on the intake fresh air amount, it is important that the intake fresh air amount is stable, and is suitable for this determination during steady operation. May not be operated for a long period of time, and the determination interval may be lengthened, so that the regeneration time may not be determined even though a large amount of particulates are collected in the particulate filter. . When the engine is decelerated when the accelerator pedal is released, the intake air amount is stable, which is suitable for determining the regeneration timing relatively frequently.
[0009]
[Problems to be solved by the invention]
However, large vehicles and the like may be provided with an exhaust throttle valve in the engine exhaust system, and when the exhaust throttle is operated to generate an exhaust brake when the engine is decelerated, the exhaust throttle valve may become a particulate filter. In the case where it is provided on the upstream side, the intake fresh air amount is reduced irrespective of the particulate collection amount, and it becomes impossible to determine the regeneration timing based on the intake fresh air amount. Also, even when the exhaust throttle valve is provided on the downstream side of the particulate filter, the pressure on the exhaust upstream side of the particulate filter is increased regardless of the amount of collected particulates, and the intake fresh air volume is also reduced. Therefore, it is impossible to accurately determine the regeneration timing based on the fresh intake air amount.
[0010]
Accordingly, an object of the present invention is to estimate the amount of particulates collected by a particulate filter disposed in the engine exhaust system at the time of deceleration, to enable accurate determination of the regeneration timing, and to be disposed in the engine exhaust system. It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine, which enables a vehicle to be favorably decelerated by an exhaust throttle valve.
[0011]
[Means for Solving the Problems]
An exhaust gas purifying apparatus for an internal combustion engine according to the present invention includes a particulate filter arranged in an engine exhaust system, an exhaust throttle valve arranged in the engine exhaust system and operated in a valve closing direction when the engine is decelerated. A new air amount detecting means for detecting a new air amount taken into the engine intake system, and a braking force determining means for determining whether or not a braking force by the exhaust throttle valve is required at the time of engine deceleration; During deceleration, when the braking force judging means determines that the braking force by the exhaust throttle valve is unnecessary, the operation of the exhaust throttle valve in the valve closing direction is stopped or the valve is operated in the valve closing direction. By opening the exhaust throttle valve and comparing the fresh air amount detected by the fresh air amount detecting means with a reference value, the amount of particulates collected by the particulate filter is reduced. Characterized in that it estimated.
[0012]
According to a second aspect of the present invention, there is provided the exhaust gas purifying apparatus for an internal combustion engine according to the first aspect, wherein the braking force determining means includes a current load weight, a currently selected transmission gear. And determining whether or not the braking force by the exhaust throttle valve is necessary based on at least one of the current vehicle speed.
[0013]
The exhaust gas purifying apparatus for an internal combustion engine according to the present invention according to claim 3 is the exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the internal combustion engine is connected to the engine exhaust system on the upstream side of the particulate filter. An engine having an exhaust gas recirculation passage communicating with an intake system, and a control valve for controlling an amount of exhaust gas to be recirculated through the exhaust gas recirculation passage to an optimum value according to an engine operating state; At the time of deceleration, when it is determined by the braking force determination means that the braking force by the exhaust throttle valve is unnecessary, the control valve is opened to a set opening and then detected by the fresh air amount detection means. The amount of collected particulates in the particulate filter is estimated by comparing the fresh air amount and a reference value.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic diagram showing an embodiment of an exhaust gas purification device for an internal combustion engine according to the present invention. In the figure, 1 is an engine main 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 disposed upstream of an intake manifold 2 a connected to each cylinder, and upstream of the throttle valve 4 is used to detect the amount of fresh air introduced into the engine intake system 2. Are 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 in its opening degree 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, a silencer, and the like.
[0016]
An exhaust gas recirculation passage 7 communicates 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. Is provided with a control valve 7a for controlling the amount of exhaust gas to be recirculated to an optimum amount according to the operating state of the engine.
[0017]
Further, the exhaust gas recirculation passage 7 is provided with an exhaust cooler 7b for cooling the recirculated exhaust gas so that a large amount of exhaust gas can be recirculated. A turbocharger turbine 8a is provided between the particulate filter 6 and the connection portion of the exhaust gas recirculation passage 7 in the engine exhaust system 3, and is provided 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 the fresh air so that a large amount of fresh air can be introduced into the cylinder. Further, an exhaust throttle valve 15 is provided downstream of the particulate filter 6 in the engine exhaust system 3 as an exhaust brake so as to reduce the passage cross-sectional area of the engine exhaust system. The exhaust throttle valve 15 is operated by a driving device (not shown) such as a step motor or a negative pressure actuator.
[0018]
The particulate filter 6 is, for example, 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 longitudinally extending partitions, and 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, the two adjacent axial spaces serve as a trap passage through which the exhaust gas flowing in from the exhaust upstream side flows out to the exhaust downstream side through the partition wall, and the partition wall made of the porous substance serves as a trap wall to allow the exhaust gas to pass therethrough. When collecting particulates.
[0019]
Further, the particulate filter 6 may be, for example, a metal fiber particulate filter composed of a nonwoven fabric of heat-resistant metal fiber and a corrugated sheet of heat-resistant metal. In this particulate filter, two nonwoven fabrics and two corrugated sheets are stacked in a thickness direction differently from each other and spirally wound, and a plurality of axial spaces are formed by the nonwoven fabrics and the corrugated sheets. Things. As the heat-resistant metal fiber forming the nonwoven fabric and the heat-resistant metal forming the corrugated sheet, for example, an Fe-Cr-Al alloy or a Ni-Cr-Al alloy can be used. The two nonwoven fabrics are continuously welded in a spiral shape with one surface in close contact with each other at the exhaust upstream end, and spirally with the other surfaces in close contact with each other at the exhaust downstream end. Welded continuously. Thus, the two axially adjacent spaces in the radial direction serve as a trap passage through which the exhaust gas flowing in from the exhaust upstream side flows out to the exhaust downstream side through any of the nonwoven fabrics. At the time of the collection of particulates.
[0020]
When a large amount of particulates are collected by the particulate filter 6, the exhaust resistance is increased and the engine output is greatly reduced. It is necessary to burn and regenerate the particulate filter itself.
[0021]
As a means for achieving this, in the present embodiment, a heater is disposed on the particulate filter, and it is necessary to determine a regeneration time for operating the heater. As a means for regenerating the particulate filter, an oxidation catalyst or the like may be arranged in the particulate filter so that unburned fuel or the like is supplied to the oxidation catalyst at the time of regeneration.
[0022]
It is not preferable that the regeneration timing 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 timing according to the flowchart shown in FIG.
[0023]
First, in step 101, it is determined whether or not the accelerator pedal depression amount L detected by an accelerator pedal stroke sensor (not shown) is zero. When this determination is denied, the accelerator pedal is depressed, that is, since the engine is operating, it is not suitable for the determination of the regeneration timing, and the process ends.
[0024]
On the other hand, when this determination is affirmative, that is, when the accelerator pedal is not depressed, the routine proceeds to step 102, where it is determined whether or not the fuel injection amount Q is zero. When this determination is denied, the fuel injection is performed and the engine is operating, so it is not suitable for the determination of the regeneration timing, and the process ends.
[0025]
However, when the determination in step 102 is affirmative, the process proceeds to step 103 because the engine is being decelerated, and the exhaust throttle valve 15 is operated in the valve closing direction. Thus, the exhaust resistance of the engine exhaust system 3 increases, and the work amount of the piston in the exhaust stroke increases, so that the exhaust brake can be generated.
[0026]
Next, in step 104, it is determined whether the loaded weight W of the luggage or the like loaded on the vehicle is equal to or less than the set weight W1. When this determination is denied, a relatively large braking force, that is, a braking force generated by an exhaust brake may be required in addition to a braking force that can be generated by a brake pedal to achieve sufficient deceleration of the vehicle, The process ends with the exhaust throttle valve 15 still operating.
[0027]
On the other hand, when the determination in step 104 is affirmative, not so large braking force is required, and the braking force by the exhaust brake may not be necessary. In step 105, the gear shift currently selected by the shift lever is performed. It is determined whether the gear is a high speed gear such as a fourth speed or a fifth speed. When this determination is denied, that is, when a low-to-medium speed gear such as the first, second, and third gears is selected, the relatively large engine is opened simultaneously with opening of the accelerator pedal without operating the exhaust throttle valve 15. Since the brake is generated, the possibility that the exhaust brake is unnecessary increases, and the process proceeds to step 107.
[0028]
On the other hand, when the high-speed gear is selected, even if the accelerator pedal is released, the engine brake is not sufficiently generated, and the possibility that the exhaust brake is required increases. However, in step 106, the brake pedal is depressed. If this determination is denied, the driver has not attempted to significantly decelerate the vehicle, and it is unlikely that an exhaust brake is required, and the process proceeds to step 107. On the other hand, when the brake pedal is depressed, the driver intends to greatly decelerate the vehicle, and since the exhaust brake is required, the operation ends with the exhaust throttle valve 15 being operated.
[0029]
In step 107, it is determined whether the current vehicle speed S is equal to or less than the set vehicle speed S1. If this determination is denied, the current vehicle speed S is high, and an exhaust brake may be required for a large deceleration, and the process ends with the exhaust throttle valve 15 being operated.
[0030]
However, when the determination in step 107 is affirmative, the loading weight W is relatively light, a low-medium-speed gear can be selected to generate a relatively large engine brake, or the high-speed gear has been selected. Since the braking force by the brake pedal is not required and the vehicle speed S is low, the driver does not need the exhaust brake to decelerate the vehicle. As a result, the exhaust throttle valve 15 is opened in step 108, and the determination of the particulate filter regeneration timing in step 109 and thereafter is performed. In the present flowchart, it is determined whether or not the exhaust brake is necessary, but this is not a limitation of the present invention. For example, the exhaust brake is determined based on at least one of the load weight, the selected gear, and the vehicle speed. It is also possible to determine whether or not the required braking force is necessary, and to estimate the actually required braking force based on the information and the actual braking force by the current engine brake and the brake pedal, and calculate the required braking force. Only when the actual braking force is exceeded, it may be determined that the exhaust brake is necessary.
[0031]
In step 109, the throttle valve 4 is set to a fully open or set opening close to full open, and in step 110, the control valve 7a is set to a fully open or set open close to full open. Next, at step 111, an intake amount reference value Gn 'to be taken into each cylinder is calculated based on the current engine speed. Of course, the reference value Gn 'for each engine speed may be mapped.
[0032]
Next, at step 112, it is determined whether or not the difference between the reference value Gn 'calculated at step 111 and the actual fresh air amount Gn detected by the air flow meter 5 is larger than a predetermined value A, and this determination is negative. At this time, it is determined that it is not the reproduction time, and the process ends. On the other hand, when the determination in step 112 is affirmative, it is determined in step 113 that it is the regeneration time, and the heater disposed in the particulate filter 6 is operated to perform the regeneration process.
[0033]
In the determination of the regeneration time of the particulate filter based on the amount of intake air, it is necessary that the amount of intake air is stable, and this is suitable for steady operation. The operation may not be performed for a long period of time, and the determination interval becomes longer. In order to accurately judge the regeneration timing of the particulate filter, it is necessary to judge the regeneration timing relatively frequently.When the engine is decelerated when the accelerator pedal is released, the intake air amount is also stable. Are suitable.
[0034]
However, when the exhaust throttle valve 15 disposed downstream of the particulate filter 6 is operated at the time of engine deceleration, the pressure upstream of the particulate filter at the upstream of the particulate filter increases even if the amount of trapped particulates is small, so that the intake new Since the air volume is reduced, the amount of trapped particulates cannot be accurately estimated based on the intake fresh air volume. Further, even when the exhaust throttle valve 15 is arranged on the upstream side of the particulate filter 6, the intake fresh air amount is simply reduced by the operation of the exhaust throttle valve 15, and the particulate collection amount based on the intake fresh air amount is reduced. Cannot be estimated.
[0035]
In the present embodiment, when the engine is decelerated, the exhaust throttle valve is once operated to generate the exhaust brake. However, in many cases, the exhaust brake is not required even when the engine is decelerated, and in this case, the exhaust throttle valve is opened. Valves are used to determine the timing of regeneration of the particulate filter based on the amount of intake air, so that accurate determination of regeneration timing is possible without lengthening the determination interval.
[0036]
Further, in the present embodiment, the exhaust brake is not generated only when it is determined that the exhaust brake is necessary, but the exhaust brake is generated simultaneously with the engine deceleration. In this case, the vehicle is sufficiently decelerated, and the driver does not feel uncomfortable due to insufficient deceleration. However, if the time for determining whether or not the exhaust brake is necessary in the current engine deceleration can be made very short by improving the control device or the like, after this determination, the exhaust throttle valve is operated as necessary. However, the exhaust brake does not occur for a very short time, and the driver does not feel uncomfortable.
[0037]
However, immediately after the accelerator pedal is released, the fluctuation of the engine speed is large, and when a turbocharger is provided as in the present embodiment, the intake air amount is not stabilized until the rotation of the compressor decreases. Accordingly, it is preferable that the determination of the regeneration timing after step 109 is not performed immediately after the accelerator pedal is released, regardless of whether the exhaust brake is generated simultaneously with the release of the accelerator pedal.
[0038]
By the way, the determination of the regeneration timing based on the intake fresh air amount is based on the fact that the intake fresh air amount decreases as the particulate collection amount increases, and the actual intake fresh air amount does not contain any particulate matter. If the reference value of the intake fresh air amount has not been reduced to, for example, 80%, it can be determined that an appropriate amount of particulates has been collected in the particulate filter and it is time to regenerate.
[0039]
However, during normal engine operation, it is necessary to stop exhaust gas recirculation when detecting the intake fresh air amount for determining the regeneration timing._XThe amount of generation increases. Accordingly, it is preferable to determine the regeneration timing at the time of engine deceleration in which the fuel is cut and the combustion is stopped, as in the present embodiment. However, at the time of engine deceleration, the reference value itself is small, so even if the actual intake fresh air amount becomes 80% of the reference value, there is a slight difference. It is necessary to measure the quantity very accurately.
[0040]
Although the present invention is not limited to this embodiment, the throttle valve 4 is increased to near the fully opened state when the engine is decelerated, so that the intake fresh air amount is increased and the reference value is increased. If the fuel is cut, there is no particular problem even if the intake new air volume is increased.Thus, even if the measurement of the intake air volume includes some errors, the regeneration timing can be determined relatively accurately. It becomes possible.
[0041]
Although the present invention is not limited thereto, in the present embodiment, the control valve of the exhaust gas recirculation passage 7 is fully opened at the time of engine deceleration. If particulates are not collected in the particulate filter 6, the pressure downstream 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, the amount of gas passing through the exhaust gas recirculation passage 7 is small, if any, so that the reference value Gn ′ is substantially equal to the actual intake fresh air amount Gn, and the determination in step 112 is negative. Is done.
[0042]
However, when the particulates are collected by 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 to cause the engine intake system. The gas starts to recirculate, and the amount increases as the amount of trapped particulates increases. Thus, the actual intake fresh air amount decreases with an increase in the exhaust resistance of the particulate filter 6 and also decreases with the recirculated gas amount.
[0043]
In this way, when an appropriate amount of particulates is collected in the particulate filter 6, a more remarkable difference occurs between the reference value Gn 'and the actual intake fresh air amount Gn. As a result, a relatively large predetermined value A can be used in step 112, and the reproduction timing can be accurately determined even if there is some measurement error. Here, the difference between the reference value Gn 'and the actual intake fresh air amount Gn is a value representing the amount of particulate collected by the particulate filter 6.
[0044]
In the present embodiment, the difference between the reference value Gn ′ and the actual intake fresh air amount Gn is used as the particulate collection amount, and when this exceeds a predetermined value A, the regeneration timing is determined. The ratio Gn / Gn ′ between the fresh air amount Gn and the reference value Gn ′ is also a value representing the particulate collection amount. This value is 1 when the trapping amount is 0, and decreases as the trapping amount increases. Thereby, when this value becomes a predetermined value (for example, 0.6), that is, when the actual intake fresh air amount Gn becomes 60% of the reference value Gn ', it is determined that the regeneration time is required. Is also good. Here, the predetermined value of 60% was used. This is a result of the gas being recirculated through the exhaust gas recirculation passage 7, and the particulate filter became difficult to pass the gas by as much as 40%. Does not mean that when the appropriate amount of particulates is collected, the amount of fresh intake air is significantly reduced as compared with the conventional case.
[0045]
FIG. 3 is a plan view showing the surrounding structure of a particulate filter 6 'different from the above-mentioned particulate filter having a regenerating means such as a heater, and FIG. 4 is a side view thereof. In this peripheral structure, the switching unit 9 connected to the downstream side of the exhaust manifold 3a via the exhaust pipe 3b, the particulate filter 6 ', and one side of the particulate filter 6' and the switching unit 9 are connected. A first connection portion 3d, a second connection portion 3e for connecting the other side of the particulate filter 6 'to the switching portion 9, and an exhaust passage 3c downstream of the switching portion 9 are provided. The switching unit 9 includes a valve body 9a that can shut off the exhaust flow in the switching unit 9. At one shutoff position of the valve body 9a, the upstream side in the switching unit 9 is communicated with the first connection unit 3d, and the downstream side in the switching unit 9 is communicated with the second connection unit 3e. As shown by the arrow, the air flows from one side of the particulate filter 6 'to the other side.
[0046]
FIG. 5 shows the other blocking position of the valve element 9a. In this shutoff position, the upstream side in the switching section 9 is communicated with the second connection section 3e, and the downstream side in the switching section 9 is communicated with the first connection section 3d, and the exhaust gas is discharged as shown by an arrow in FIG. , Flows from the other side of the particulate filter 6 'to one side. Thus, by switching the valve element 9a, the direction of the exhaust gas flowing into the particulate filter 6 'can be reversed, that is, the exhaust gas upstream and the exhaust downstream of the particulate filter 6' can be reversed. It becomes possible.
[0047]
In this way, the structure surrounding the present 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 to facilitate the inflow of exhaust gas. However, the structure around the particulate filter does not deteriorate the vehicle mountability, and the structure shown in FIGS. As shown in (1), a particulate filter having a large opening area can be used.
[0048]
FIG. 6 shows the structure of the particulate filter 6 '. 6A is a front view of the particulate filter 6 ', and FIG. 6B is a side sectional view. As shown in these figures, the particulate filter 6 ′ has an elliptical 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 axially extending partitions 54. In two adjacent axial spaces, one is closed on the exhaust downstream side and the other is closed on the exhaust upstream side by plugs 52,53. Thus, 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 the arrow in FIG. 6B. Although the particulates in the exhaust gas are very small compared to the size of the pores of the partition wall 54, they collide with and are trapped on the exhaust upstream surface of the partition wall 54 and the pore surface in the partition wall 54. Gathered. Thus, each partition wall 54 functions as a collecting wall for collecting particulates. In the present particulate filter 6 ′, in order to oxidize and remove the trapped particulates, the following description will be given using alumina or the like on both surfaces of the partition walls 54, and preferably on the pore surfaces in the partition walls 54. An active oxygen releasing agent and a noble metal catalyst are supported.
[0049]
The active oxygen releasing agent promotes the oxidation of particulates by releasing active oxygen.Preferably, when there is excess oxygen in the surroundings, it takes in oxygen to retain oxygen and reduce the surrounding oxygen concentration. When lowered, the retained oxygen is released in the form of active oxygen.
[0050]
As this noble metal catalyst, platinum Pt is usually used, and as an active oxygen releasing agent, potassium K, sodium Na, lithium Li, cesium Cs, alkali metal such as rubidium Rb, barium Ba, calcium Ca, strontium Sr. At least one selected from such alkaline earth metals, lanthanum La, rare earths such as yttrium Y, and transition metals is used.
[0051]
In this case, as the active oxygen releasing agent, an alkali metal or an 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 may be used. preferable.
[0052]
Next, how the collected particulates are oxidized and removed by the particulate filter supporting such an active oxygen releasing agent will be described with reference to platinum Pt and potassium K as an example. The same particulate removal effect can be obtained by using other noble metals, alkali metals, alkaline earth metals, rare earths, and transition metals.
[0053]
Diesel engines usually burn under excess air, so 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. Further, the fuel contains sulfur S, which reacts with oxygen in the combustion chamber to produce SO.₂It becomes. Therefore, SO in the exhaust gas₂It is included. Thus, excess oxygen, NO and SO₂Will flow into the particulate filter 6 'upstream of the exhaust gas.
[0054]
FIGS. 7A and 7B schematically show enlarged views of the exhaust gas contact surface of the particulate filter 6 '. 7A and 7B, reference numeral 60 denotes platinum Pt particles, and reference numeral 61 denotes an active oxygen releasing agent containing potassium K.
[0055]
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.₂Is O₂ ⁻Or O^2-On the surface of platinum Pt. On the other hand, NO in the exhaust gas becomes O 2 on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with NO₂(2NO + O₂→ 2NO₂). NO generated next₂Is absorbed in the active oxygen releasing agent 61 while being oxidized on the platinum Pt, and combined with potassium K to form nitrate ions NO as shown in FIG.₃ ⁻Is diffused into the active oxygen releasing agent 61 in the form of potassium nitrate KNO₃Generate In this way, the harmful NO contained in the exhaust gas_XIs absorbed by the particulate filter 6 ', and the amount of emission into the atmosphere can be greatly reduced.
[0056]
On the other hand, as described above, SO2 is contained in the exhaust gas.₂Is also included in this SO₂Is also absorbed into the active oxygen releasing agent 61 by the same mechanism as NO. That is, as described above, the oxygen O₂Is O₂ ⁻Or O^2-Is attached to the surface of platinum Pt in the form of₂Is O on the surface of platinum Pt₂ ⁻Or O^2-Reacts with SO₃It becomes. Then the generated SO₃Is absorbed in the active oxygen releasing agent 61 while being further oxidized on the platinum Pt, and combined with potassium K to form sulfate ions SO.₄ ^2-In the active oxygen releasing agent 61 in the form of potassium sulfate K₂SO₄Generate Thus, potassium nitrate KNO is contained in the active oxygen release catalyst 61.₃And potassium sulfate K₂SO₄Is generated.
[0057]
The particulates in the exhaust gas adhere to the surface of the active oxygen releasing agent 61 carried on the particulate filter, as indicated by 62 in FIG. 7B. At this time, the oxygen concentration decreases at the contact surface between the particulate 62 and the active oxygen releasing agent 61. When the oxygen concentration decreases, a concentration difference occurs between the active oxygen releasing agent 61 having a high oxygen concentration and the oxygen in the active oxygen releasing agent 61. Try to move towards. As a result, potassium nitrate KNO formed in the active oxygen releasing agent 61₃Is decomposed into potassium K, oxygen O and NO, oxygen O is directed to the contact surface between the particulate 62 and the active oxygen releasing agent 61, and NO is released from the active oxygen releasing agent 61 to the outside. The NO released to the outside is oxidized on platinum Pt on the downstream side, and is again absorbed in the active oxygen releasing agent 61.
[0058]
On the other hand, at this time, potassium sulfate K formed in the active oxygen releasing agent 61₂SO₄Also potassium K, oxygen O and SO₂Oxygen O is directed to the contact surface between the particulate 62 and the active oxygen releasing agent 61,₂Is released from the active oxygen releasing agent 61 to the outside. SO released outside₂Is oxidized on platinum Pt on the downstream side, and is again absorbed in the active oxygen releasing agent 61. However, potassium sulfate K₂SO₄Is stable because potassium nitrate KNO₃It is difficult to release active oxygen as compared with.
[0059]
On the other hand, oxygen O toward the contact surface between the particulate 62 and the active oxygen releasing agent 61 is potassium nitrate KNO₃And potassium sulfate K₂SO₄Is oxygen decomposed from such a compound. Oxygen O decomposed from the compound has high energy and extremely high activity. Therefore, the oxygen going to the contact surface between the particulate 62 and the active oxygen releasing agent 61 is active oxygen O. When the active oxygen O comes into contact with the particulate 62, the particulate 62 is oxidized without emitting a bright flame.
[0060]
Incidentally, the platinum Pt and the active oxygen releasing agent 61 are activated as the temperature of the particulate filter increases, so that the amount of active oxygen O released from the active oxygen releasing agent 61 per unit time increases as the temperature of the particulate filter increases. I do. Therefore, the amount of oxidizable particles that can oxidize and remove particulates per unit time on the particulate filter without emitting luminous flame per unit time increases as the temperature of the particulate filter increases.
[0061]
The solid line in FIG. 8 indicates the amount G of the oxidizable and removable fine particles that can be oxidized and removed without emitting a bright flame per unit time. In FIG. 8, the horizontal axis represents the temperature TF of the particulate filter. When the amount of particulates discharged from the combustion chamber per unit time is referred to as the amount M of discharged fine particles, when the amount M of discharged fine particles is smaller than the amount G of fine particles that can be removed by oxidation, that is, in the region I in FIG. As soon as all the particulates collected are collected by the particulate filter, the particulate filter is oxidized and removed within a short period of time without emitting a bright flame.
[0062]
On the other hand, when the amount M of discharged fine particles is larger than the amount G of fine particles that can be removed by oxidation, that is, in the region II in FIG. 8, the amount of active oxygen is insufficient to oxidize all the particulates. FIGS. 9A to 9C show how the particulates are oxidized in such a case.
[0063]
That is, when the amount of active oxygen is insufficient to oxidize all the particulates, when the particulates 62 adhere to the active oxygen releasing agent 61 as shown in FIG. Only the particulates are oxidized, and the particulates that have not been sufficiently oxidized remain on the exhaust upstream side of the particulate filter. Next, when the state of the shortage of the active oxygen amount continues, the particulate portion which 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.
[0064]
Such a residual particulate portion 63 is gradually transformed into a carbon material which is hardly oxidized, and when the exhaust upstream surface is covered with the residual particulate portion 63, NO, SO by platinum Pt is formed.₂And the active oxygen releasing action of the active oxygen releasing agent 61 is suppressed. Thereby, the residual particulate portion 63 can be gradually oxidized with time, but another particulate 64 is placed on the residual particulate portion 63 one after another as shown in FIG. 9C. In other words, when the particulates are deposited in a layered manner, these particulates are spaced apart from platinum Pt and the active oxygen releasing agent. It is not oxidized. Therefore, further particulates accumulate on this particulate 64 one after another. In other words, if the state in which the amount M of discharged fine particles is larger than the amount G of fine particles that can be removed by oxidation continues, the particulates will be deposited in layers on the particulate filter.
[0065]
As described above, in the region I of FIG. 8, the particulates are oxidized in a short time without emitting a bright flame on the particulate filter, and in the region II of FIG. 8, the particulates are deposited on the particulate filter in a stacked manner. I do. Therefore, if the relationship between the discharged fine particle amount M and the oxidizable and removable fine particle amount G is set to the region I, it is possible to prevent the accumulation of particulates on the particulate filter. However, this is not always achieved, and if nothing is done, particulates may accumulate on the particulate filter.
[0066]
Before the accumulation of the particulates has an adverse effect on the traveling of the vehicle, for example, when the particulates accumulate to the extent shown in FIG. Then, as the regeneration process, the valve element 9a may be switched to the other shutoff position. In the wall flow type particulate filter, the particulates collide with the exhaust gas mainly on the upstream side surface of the partition wall 54 where the exhaust gas collides and the exhaust gas flow opposing surface in the pores, that is, on one collecting surface of the partition wall 54. If the release of active oxygen from one of the trapping surfaces is insufficient for the trapped particulates, all of them remain without being oxidized and removed, and the remaining particulates are successively deposited. I do.
[0067]
If the upstream side and the downstream side of the exhaust of the particulate filter are reversed by the switching of the valve element 9a, no more particulate will accumulate on the particulate accumulated on one collection surface of the partition. The residual and deposited particulates are gradually oxidized and removed by the active oxygen released from one of the collecting surfaces. Further, particularly, the particulates remaining and deposited in the pores of the partition walls are easily broken down and fragmented by the exhaust gas flow in the opposite direction, as shown in FIG. Move downstream.
[0068]
As a result, many of the finely divided particulates are dispersed in the pores of the partition walls, and there are many opportunities to be oxidized and removed by directly contacting the active oxygen releasing agent carried on the inner surfaces of the partition wall pores. Become. By carrying the active oxygen releasing agent also in the pores of the partition walls, the residual and deposited particulates can be remarkably easily oxidized and removed. Furthermore, in addition to this oxidation removal, the other trapping 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 currently mainly collides and the inside of the pores On the exhaust gas flow-facing surface (which is on the opposite side 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 releasing agent. . A part of the active oxygen released from the active oxygen releasing agent at the time of these oxidative removal moves downstream together with the exhaust gas, and oxidizes and removes the particulates remaining and deposited by the backflow of the exhaust gas.
[0069]
In other words, not only the active oxygen released from this collecting surface but also the oxidation of the particulates on the other collecting surface of the partition due to the backflow of the exhaust gas is caused by the residual and deposited particulates on one collecting surface of the partition. The remaining active oxygen used for removal 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 the particulates are deposited to some extent on one of the collecting surfaces of the particulate filter partition wall at the time of reverse rotation, the residual gas and the active oxygen also arrive at the deposited particulates due to the backflow of the exhaust gas. The residual and deposited particulates are gradually oxidized and removed because no further particulates are deposited. Then, the particulates remain and accumulate on the other trapping surface where the particulates are currently trapped, so that the regenerating time is reached and the valve element 9a is switched again, so that the particulates remain and accumulate on one collecting surface. Can be sufficiently removed by oxidation.
[0070]
Further, when the air-fuel ratio of the exhaust gas is made rich, that is, when the oxygen concentration in the exhaust gas is reduced, active oxygen O is released from the active oxygen releasing agent 61 to the outside at a stretch, and the active oxygen O released at a stretch accumulates. The particulates can be burned and removed at once without emitting a bright flame. In this way, if the air-fuel ratio of the exhaust gas is made rich when the exhaust gas upstream and downstream of the particulate filter are reversed by the valve element 9a or immediately thereafter, the particulates in the particulate filter partition remain and accumulate. On the other collecting surface, the active oxygen is released more easily than on the other collecting surface. Therefore, the residual and deposited particulates are more reliably oxidized and removed by the active oxygen released in a larger amount. It is possible to do.
[0071]
By the way, calcium Ca in the exhaust gas is SO₃Is present, calcium sulfate CaSO such as ash₄Generate This calcium sulfate CaSO₄In order to prevent the particulate filter from being clogged, an alkali metal or an alkaline earth metal having a higher ionization tendency than calcium Ca, such as potassium K, is used as the active oxygen releasing agent 61 to diffuse into the active oxygen releasing agent 61. SO₃Combines with potassium K to form potassium sulfate K₂SO₄And calcium Ca is SO₃Pass through the partition of the catalytic converter without being combined with. Therefore, the particulate filter is not clogged by the ash. Thus, as described above, as the active oxygen releasing 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, and strontium Sr is used. Is preferred.
[0072]
Further, even if only a noble metal such as platinum Pt is supported on the particulate filter, NO held on the surface of platinum Pt₂Or SO₃Can release active oxygen. However, in this case, the solid line indicating the amount of fine particles G that can be removed by oxidation moves slightly to the right as compared with the solid line shown in FIG. Ceria can also be used as an active oxygen releasing agent. Ceria absorbs oxygen when the oxygen concentration in the exhaust gas is high, and releases active oxygen when the oxygen concentration in the exhaust gas decreases.Therefore, the exhaust gas is evacuated to remove particulates by oxidation. The fuel ratio needs to be enriched regularly or irregularly.
[0073]
Also, NO in the exhaust gas is used as an active oxygen releasing agent._XNO used for purification_XIt is also possible to use a storage reduction catalyst. In this case, the stored NO_XAnd SO_XIt is necessary to at least temporarily make the air-fuel ratio of the exhaust gas rich in order to discharge the exhaust gas, and it is preferable to perform this enrichment control after the reversal of the upstream and downstream sides of the particulate filter.
[0074]
【The invention's effect】
Thus, according to the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the particulate filter disposed in the engine exhaust system and the exhaust throttle valve disposed in the engine exhaust system and operated in the valve closing direction when the engine is decelerated are provided. A new air amount detecting means for detecting a new air amount introduced into the engine intake system, and a braking force judging means for judging whether or not a braking force by an exhaust throttle valve is necessary at the time of engine deceleration. When the braking force judging means determines that the braking force by the exhaust throttle valve is unnecessary, the operation of the exhaust throttle valve in the valve closing direction is stopped or the exhaust throttle operated in the valve closing direction is stopped. By opening the valve and comparing the fresh air amount detected by the fresh air amount detecting means with a reference value, the amount of particulate trapped in the particulate filter is estimated. Accordingly, when the braking force determination means determines that the braking force by the exhaust throttle valve is necessary at the time of engine deceleration, the exhaust throttle valve is operated in the valve closing direction to generate an exhaust brake, and the vehicle is satisfactorily decelerated. It is possible. Further, when the engine is decelerated, if the braking force judging means judges that the braking force by the exhaust throttle valve is unnecessary, the operation of the exhaust throttle valve in the valve closing direction is stopped or the exhaust throttle valve is already operated in the valve closing direction. By opening the exhaust throttle valve to prevent the occurrence of an exhaust brake, enabling the estimation of the particulate collection amount based on the fresh air amount, and performing this estimation, the particulate collection is performed relatively frequently. The amount of collection can be accurately estimated, and the timing of regeneration of the particulate filter can be accurately determined.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an embodiment of an exhaust gas purification device for an internal combustion engine according to the present invention.
FIG. 2 is a flowchart for determining a reproduction time.
FIG. 3 is a plan view showing a surrounding structure of another particulate filter.
FIG. 4 is a side view of FIG. 3;
FIG. 5 is a view showing another shut-off position of the valve body in the switching unit different from FIG. 3;
FIG. 6 is a diagram showing a structure of a particulate filter.
FIG. 7 is a diagram for explaining the oxidizing action of particulates.
FIG. 8 is a diagram showing the relationship between the amount of fine particles that can be removed by oxidation and the temperature of a particulate filter.
FIG. 9 is a diagram for explaining a particulate deposition action.
FIG. 10 is an enlarged sectional view of a partition wall of the particulate filter.
[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
15 ... Exhaust throttle valve
20 ... Control device

Claims (3)

A particulate filter arranged in the engine exhaust system, an exhaust throttle valve arranged in the engine exhaust system to operate in the valve closing direction when the engine is decelerated, and a new air amount detection for detecting a new air amount taken into the engine intake system And braking force determining means for determining whether or not the braking force by the exhaust throttle valve is necessary when the engine is decelerated. When the engine is decelerated, the braking force by the exhaust throttle valve is determined by the braking force determining means. When it is determined that the exhaust throttle valve is unnecessary, the operation of the exhaust throttle valve in the valve closing direction is stopped or the exhaust throttle valve operated in the valve closing direction is opened and the fresh air amount detecting means is opened. An exhaust gas purifying apparatus for an internal combustion engine, which estimates the amount of particulates trapped in the particulate filter by comparing the fresh air amount detected by the method with a reference value. The braking force determination means determines whether or not a braking force by the exhaust throttle valve is necessary based on at least one of a current load weight, a currently selected transmission gear, and a current vehicle speed. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1. The internal combustion engine is configured such that an exhaust gas recirculation passage communicating the upstream of the particulate filter of an engine exhaust system and an engine intake system, and an exhaust gas amount to be recirculated through the exhaust gas recirculation passage to an engine operating state. And a control valve for controlling the control valve to a corresponding optimum value. When the braking force determining means determines that the braking force by the exhaust throttle valve is unnecessary during engine deceleration, the control valve is set. After the valve is opened to an opening degree, the fresh air amount detected by the fresh air amount detecting means is compared with a reference value to estimate a particulate trapping amount in the particulate filter. Item 2. An exhaust gas purification device for an internal combustion engine according to item 1.

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