JP2004257267A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique of removing PM adhered to the upstream end of the front-stage catalyst provided upstream of a particulate filter while suppressing dilution of a lubricating oil or generation of bore flashing in an exhaust emission control system of an internal combustion engine. <P>SOLUTION: The system has an oxidation catalyst, a particulate filter downstream of the catalyst, a fuel supply means, a filter regeneration means removing PM piled in the filter by fuel supply, and a front-stage catalyst regeneration means removing PM piled in the catalyst by raising exhaust temperature. An interval for removing PM piled in the front stage of the catalyst is set to be longer than that for the regeneration of the filter, thereby suppressing the oil dilution. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification system for an internal combustion engine.
[0002]
[Prior art]
In recent years, removal of particulate matter (hereinafter, referred to as “PM”) represented by soot, which is a suspended particulate matter contained in exhaust gas of diesel engines, has become an important issue. For this reason, there is known a technique of providing a particulate filter (hereinafter, simply referred to as a “filter”) for capturing PM in an exhaust system so that PM is not released into the atmosphere.
[0003]
This filter can prevent PM in exhaust gas from being once captured and released into the atmosphere. However, when PM trapped by the filter accumulates on the filter, the filter may be clogged. When the clogging occurs, the pressure of the exhaust gas upstream of the filter increases, which may cause a decrease in the output of the internal combustion engine or damage to the filter. In such a case, the PM deposited on the filter can be removed by oxidizing the PM. Removing PM accumulated on the filter in this way is called filter regeneration.
[0004]
As a technique for regenerating the filter, for example, a technique for increasing the temperature of exhaust gas by an oxidation action of an oxidation catalyst upstream of the filter to oxidize PM captured by the filter (for example, see Patent Document 1), a storage reduction type NOx A particulate filter carrying a catalyst and a NOx catalyst having an oxidizing ability upstream of the particulate filter, and a technique for oxidizing SOF components with the NOx catalyst (for example, see Patent Document 2); ₂ To generate this NO ₂ (For example, see Patent Document 3) is known.
[0005]
[Patent Document 1]
JP-A-8-313331 (page 4-7, FIG. 1)
[Patent Document 2]
JP-A-2002-115524 (page 3-13, FIG. 18)
[Patent Document 3]
Japanese Patent No. 3012249 (page 2-12, FIG. 1)
[0006]
[Problems to be solved by the invention]
By the way, when a catalyst for raising the temperature of the filter is provided upstream of the filter, PM may adhere to the catalyst. Here, the PM deposited on the filter can be removed by adding fuel in the exhaust gas. However, with the catalyst provided upstream, the temperature of the upstream end of the catalyst does not increase, so that the PM adhering to this upstream end is removed. Removal of PM becomes difficult. On the other hand, by increasing the temperature itself of the exhaust gas discharged from the internal combustion engine, it is possible to oxidize PM attached to the upstream end.
[0007]
However, in order to raise the temperature of the exhaust gas from the internal combustion engine, if the fuel injection timing is delayed or if the sub-injection is performed in addition to the main injection, dilution of the lubricating oil with this fuel and washing of the lubricating oil on the cylinder wall are performed. Flushing may occur, and furthermore, the seizure of the piston may occur.
[0008]
The present invention has been made in view of the above-described problems, and in an exhaust gas purification system for an internal combustion engine, while suppressing dilution and bore flushing of lubricating oil, a pre-catalyst provided upstream of a particulate filter is provided. An object of the present invention is to provide a technique for removing PM attached to an upstream end.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an exhaust gas purification system for an internal combustion engine according to the present invention employs the following means. That is,
A catalyst provided in the exhaust passage of the internal combustion engine and having an oxidizing ability,
A particulate filter provided downstream of the oxidizing catalyst and trapping particulate matter in exhaust gas;
Fuel supply means for supplying fuel into the exhaust from upstream of the catalyst having oxidizing ability;
Filter regeneration means for supplying fuel by fuel supply means and removing particulate matter deposited on the particulate filter,
A first-stage catalyst regenerating means for increasing the temperature of exhaust gas upstream of the oxidizing catalyst to remove deposits deposited on the oxidizing catalyst,
It is characterized by having.
[0010]
The most significant feature of the present invention is that it comprises a filter regenerating means and a pre-catalyst regenerating means, and removes deposits by means different from each other between a particulate filter and a catalyst having an oxidizing ability.
[0011]
In the exhaust gas purification system for an internal combustion engine configured as described above, the particulate matter deposited on the particulate filter is removed by the filter regeneration means. Here, when the fuel is supplied from the fuel supply means into the exhaust gas, the fuel is oxidized by an upstream oxidizing catalyst, and heat is generated. Further, when the particulate filter has an oxidizing ability, heat is also generated in the particulate filter. This heat oxidizes and removes the particulate matter deposited on the particulate filter. However, at the upstream end of the catalyst having the oxidizing ability, the temperature rise is slow, and the oxidation of the particulate matter is slow. Here, it is possible to oxidize and remove particulate matter attached to the upstream end by raising the temperature of the exhaust gas by the former-stage catalyst regenerating means and flowing the high-temperature exhaust gas through the oxidizing catalyst. Since the temperature of the exhaust gas is raised only when deposits of the catalyst having oxidizing ability are removed, it is possible to suppress the number of times of dilution of lubricating oil and occurrence of bore flushing.
[0012]
In the present invention, the apparatus further comprises a pre-stage catalyst regeneration timing determining means for determining a timing of removing the deposits deposited on the catalyst having the oxidizing ability, and it is a timing to remove the deposits by the pre-catalyst regeneration timing determining means. When the determination is made, when the particulate matter deposited on the filter is removed by the filter regenerating means, the pre-stage catalyst regenerating means can increase the temperature of the exhaust gas.
[0013]
In the exhaust gas purification system for an internal combustion engine configured as described above, when it is determined by the preceding catalyst regeneration timing determination means that it is time to remove the deposits accumulated on the catalyst having the oxidizing ability, the filter regeneration means determines When removing particulate matter deposited on the particulate filter, the temperature of the exhaust gas is increased by the pre-stage catalyst regeneration means. By increasing the temperature of the exhaust gas, it becomes possible to simultaneously remove the deposits from the catalyst having the oxidizing ability and the particulate filter.
[0014]
In the present invention, the interval at which deposits are removed by the pre-stage catalyst regenerating means can be longer than the interval at which particulate matter is removed by the filter regenerating means.
[0015]
A catalyst having an oxidizing ability has a smaller amount of particulate matter and the like attached thereto than a particulate filter. Therefore, the interval at which the deposits accumulated on the oxidizing catalyst by the former catalyst regeneration unit may be removed may be longer than the interval at which the deposits accumulated on the particulate filter by the filter regeneration unit are removed. By increasing the interval between the removal of the deposits by the pre-catalyst regenerating means, the number of times the lubricating oil is diluted or bore flushing can be suppressed.
[0016]
In the present invention, the apparatus further comprises a deposition amount estimating means for estimating the amount of deposits deposited on the catalyst having the oxidizing ability, wherein the filter regeneration means removes the deposits deposited on the filter, and the former catalyst regeneration means comprises The temperature of the exhaust gas can be increased as the amount of the deposit estimated by the accumulation amount estimating means increases.
[0017]
There is a correlation between the amount of reduced catalyst deposits having oxidizing ability and the temperature of exhaust gas. In other words, the higher the temperature of the exhaust gas, the greater the amount of deposits deposited on the catalyst having oxidizing ability. Therefore, by raising the temperature of the exhaust gas in accordance with the amount of deposits deposited on the catalyst having oxidizing ability, it is possible to raise the minimum required temperature, and the particulate matter deposited on the catalyst having oxidizing ability and the particulate filter can be obtained. It is possible to suppress the number of times the dilution of the lubricating oil and the bore flushing occur while simultaneously removing the substance.
[0018]
In the present invention, the apparatus further comprises a deposition amount estimating means for estimating the amount of the deposit deposited on the catalyst having the oxidizing ability, and when the amount of the deposit estimated by the deposition amount estimating means exceeds an allowable range. The deposits can be removed by the first-stage catalyst regeneration means.
[0019]
Accordingly, regardless of the amount of the particulate matter deposited on the particulate filter or the removal of the particulate matter by the filter regenerating means, the exhaust gas is discharged when it becomes necessary to remove the deposit deposited on the oxidizing catalyst. It is possible to raise the temperature.
[0020]
In the present invention, the apparatus further comprises exhaust gas temperature detecting means for detecting the temperature of exhaust gas flowing into the catalyst having the oxidizing ability, wherein the deposition amount estimating means increases as the temperature of the exhaust gas detected by the exhaust gas temperature detecting means increases. It can be determined that the amount of deposits deposited on the catalyst having the oxidation ability decreases.
[0021]
The higher the temperature of the exhaust gas flowing into the catalyst having the oxidizing ability, the greater the amount of particulate matter oxidized on the catalyst is oxidized, and the smaller the amount of particulate matter deposited. Therefore, the deposit amount estimating means can estimate that the amount of deposits decreases when the high-temperature exhaust gas flows into the catalyst having the oxidizing ability.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
<First embodiment>
Hereinafter, specific embodiments of an exhaust gas purification system for an internal combustion engine according to the present invention will be described with reference to the drawings. Here, an example in which the exhaust gas purification system for an internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described.
[0023]
FIG. 1 is a diagram showing a schematic configuration of an engine 1 to which an exhaust purification system according to the present embodiment is applied and an intake / exhaust system thereof.
[0024]
The engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.
[0025]
The engine 1 includes a fuel injection valve 3 for directly injecting fuel into a combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulation chamber (common rail) 4 for accumulating fuel up to a predetermined pressure.
[0026]
The common rail 4 communicates with a fuel pump 6 via a fuel supply pipe 5. The fuel pump 6 is a pump that operates by using a rotational torque of an output shaft (crankshaft) of the engine 1 as a driving source. A pump pulley 6a attached to an input shaft of the fuel pump 6 has an output shaft (crankshaft) of the engine 1. ) Are connected via a belt 7 to a crank pulley 1a attached to the crank pulley 1).
[0027]
In the fuel injection system configured as described above, when the rotation torque of the crankshaft is transmitted to the input shaft of the fuel pump 6, the fuel pump 6 rotates the rotation torque transmitted from the crankshaft to the input shaft of the fuel pump 6. The fuel is discharged at a pressure according to.
[0028]
The fuel discharged from the fuel pump 6 is supplied to a common rail 4 via a fuel supply pipe 5, accumulated in the common rail 4 to a predetermined pressure, and distributed to the fuel injection valves 3 of each cylinder 2. When a drive current is applied to the fuel injection valve 3, the fuel injection valve 3 opens, and as a result, fuel is injected from the fuel injection valve 3 into the cylinder 2.
[0029]
Next, an intake branch pipe 8 is connected to the engine 1, and each branch pipe of the intake branch pipe 8 communicates with a combustion chamber of each cylinder 2 via an intake port (not shown).
[0030]
The intake branch pipe 8 is connected to an intake pipe 9. An air flow meter 11 that outputs an electric signal corresponding to the mass of intake air flowing through the intake pipe 9 is attached to the intake pipe 9.
[0031]
An intake throttle valve 13 for adjusting the flow rate of intake air flowing through the intake pipe 9 is provided at a position of the intake pipe 9 located immediately upstream of the intake branch pipe 8. The intake throttle valve 13 is provided with an intake throttle actuator 14 which is configured by a step motor or the like and drives the intake throttle valve 13 to open and close.
[0032]
An intake pipe 9 located between the air flow meter 11 and the intake throttle valve 13 is provided with a compressor housing 15a of a centrifugal supercharger (turbocharger) 15 that operates using exhaust energy as a driving source.
[0033]
In the intake system configured as described above, the intake air flows into the compressor housing 15a via the intake pipe 9.
[0034]
The intake air flowing into the compressor housing 15a is compressed by rotation of a compressor wheel provided inside the compressor housing 15a. The intake air compressed in the compressor housing 15a flows into the intake branch pipe 8 with the flow rate adjusted by the intake throttle valve 13 as necessary. The intake air flowing into the intake branch pipe 8 is distributed to the combustion chamber of each cylinder 2 via each branch pipe, and is burned using the fuel injected from the fuel injection valve 3 of each cylinder 2 as an ignition source.
[0035]
On the other hand, an exhaust branch pipe 18 is connected to the engine 1, and each branch pipe of the exhaust branch pipe 18 communicates with a combustion chamber of each cylinder 2 via an exhaust port 1b.
[0036]
The exhaust branch pipe 18 is connected to a turbine housing 15 b of the centrifugal supercharger 15. The turbine housing 15b is connected to an exhaust pipe 19, which communicates downstream with the atmosphere.
[0037]
In the middle of the exhaust pipe 19, a storage-reduction type NOx catalyst (hereinafter, simply referred to as NOx catalyst) is supported, and particulate matter represented by soot, which is a suspended particulate matter contained in exhaust gas, is used. Matter: a particulate filter (hereinafter, simply referred to as a filter) 20 for capturing PM is provided.
[0038]
Here, the filter 20 according to the present embodiment will be described.
[0039]
FIG. 2 is a sectional view of the filter 20. FIG. 2A is a diagram showing a cross section of the filter 20 in the lateral direction. FIG. 2B is a diagram illustrating a vertical cross section of the filter 20.
[0040]
As shown in FIGS. 2A and 2B, the filter 20 is a so-called wall flow type having a plurality of exhaust passages 50 and 51 extending parallel to each other. These exhaust passages include an exhaust inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust outflow passage 51 whose upstream end is closed by a plug 53. In FIG. 2A, hatched portions indicate plugs 53. Accordingly, the exhaust inflow passages 50 and the exhaust outflow passages 51 are alternately arranged with the thin partition walls 54 interposed therebetween. In other words, the exhaust inflow passage 50 and the exhaust outflow passage 51 are arranged such that each exhaust inflow passage 50 is surrounded by four exhaust outflow passages 51 and each exhaust outflow passage 51 is surrounded by the four exhaust inflow passages 50.
[0041]
The filter 20 is formed of a porous material such as cordierite, so that the exhaust gas flowing into the exhaust inflow passage 50 passes through the surrounding partition wall 54 as shown by an arrow in FIG. Out of the exhaust passage 51.
[0042]
In this embodiment, a carrier layer made of, for example, alumina is formed on the peripheral wall surface of each exhaust inflow passage 50 and each exhaust outflow passage 51, that is, on both side surfaces of each partition wall 54 and on the inner wall surface of the pores in the partition wall 54. The NOx storage reduction catalyst is supported on this carrier.
[0043]
The filter 20 includes, for example, alumina as a carrier, and an alkali metal such as potassium (K), sodium (Na), lithium (Li), or cesium (Cs) and barium (Ba) or calcium (Ca) on the carrier. ) And at least one selected from rare earths such as lanthanum (La) or yttrium (Y) and a noble metal such as platinum (Pt). In the present embodiment, an NOx storage reduction catalyst (hereinafter, simply referred to as a NOx catalyst) constituted by supporting barium (Ba) and platinum (Pt) on a carrier made of alumina is employed. Furthermore, O ₂ Ceria with storage capacity (Ce ₂ O ₃ ) May be added.
[0044]
When the oxygen concentration of the exhaust gas flowing into the filter 20 is high, the occlusion-reduction type NOx catalyst carried by the filter 20 occludes (may absorb or adsorb) nitrogen oxides (NOx) in the exhaust gas. When the oxygen concentration of the exhaust gas flowing into the filter 20 decreases, the stored NOx is released. At this time, if fuel such as hydrocarbon (HC) or carbon monoxide (CO) is present in the exhaust gas, NOx released from the NOx storage reduction catalyst is reduced. Ceria (CeO) ₂ Transition metals such as) have the ability to temporarily hold oxygen depending on the characteristics of the exhaust and release it as activated oxygen.
[0045]
On the other hand, the PM in the exhaust gas is once captured by the filter 20 and is prevented from being released into the atmosphere.
[0046]
Note that the filter 20 is not limited to a filter supporting the storage reduction type NOx catalyst, and may be a particulate filter not supporting a catalyst, or a filter supporting an oxidation catalyst or a three-way catalyst. good.
[0047]
An upstream catalyst 21 supporting an NOx storage reduction catalyst is provided upstream of the filter 20. The pre-catalyst 21 has a smaller capacity than the filter 20, and the temperature can be quickly increased by the heat of the exhaust gas even when the engine is started, and the catalyst can be activated. The first-stage catalyst 21 may be any catalyst having an oxidizing ability, and may be, for example, an oxidation catalyst or a three-way catalyst in place of the NOx storage reduction catalyst.
[0048]
The first-stage catalyst 21 employs a ceramic carrier, and is formed so that the carrier has a monolith shape or a honeycomb shape in order to increase a contact area with exhaust gas. A through-hole is provided in the exhaust gas flow direction, and the cross-sectional shape of the through-hole is a lattice. Further, in the present embodiment, a metal carrier can be employed for the pre-stage catalyst 21. In the metal carrier, a long laminated material is formed by laminating a corrugated sheet on a flat plate, and then the long laminated material is rolled and formed into a cylindrical shape. And the storage reduction type NOx catalyst is carried on the carrier.
[0049]
An exhaust temperature sensor 22 that outputs an electric signal corresponding to the temperature of exhaust flowing through the exhaust pipe 19 is attached to the exhaust pipe 19 upstream of the pre-catalyst 21.
[0050]
In the exhaust system configured as described above, the air-fuel mixture (burned gas) burned in each cylinder 2 of the engine 1 is discharged to the exhaust branch pipe 18 through the exhaust port 1b, and then centrifuged from the exhaust branch pipe 18. It flows into the turbine housing 15b of the feeder 15. The exhaust gas flowing into the turbine housing 15b rotates a turbine wheel rotatably supported in the turbine housing 15b by using energy of the exhaust gas. At this time, the rotational torque of the turbine wheel is transmitted to the compressor wheel of the compressor housing 15a described above.
[0051]
The exhaust gas discharged from the turbine housing 15b flows into the pre-stage catalyst 21 and the filter 20 via the exhaust pipe 19, and NOx in the exhaust gas is stored in the storage-reduction NOx catalyst, and the filter 20 captures PM. Thereafter, the exhaust gas flows through the exhaust pipe 19 and is discharged into the atmosphere.
[0052]
By the way, when the PM captured by the filter 20 accumulates on the filter 20, the filter 20 may be clogged. When the clogging occurs, the pressure of the exhaust gas upstream of the filter 20 increases, which may cause a decrease in the output of the engine 1 or damage to the filter 20. In such a case, the PM deposited on the filter 20 can be removed by oxidizing the PM. Removing PM accumulated on the filter in this way is called filter regeneration. The regeneration of the filter 20 is performed by supplying, for example, hydrocarbon (HC) or carbon monoxide (CO), which generates heat of oxidation reaction in the pre-catalyst 21 or the filter 20, to the pre-catalyst 21 or the filter 20, and generating heat at this time. Also, this is made possible by the heat of the exhaust gas having a higher temperature than usual.
[0053]
Therefore, when the temperature of the exhaust gas from the engine 1 is low, hydrocarbon (HC), carbon monoxide (CO), or the like is supplied to the filter 20 or the pre-catalyst 21 before the filter 20 is clogged. Alternatively, it is necessary to oxidize the PM deposited on the filter 20 by increasing the temperature of the exhaust gas.
[0054]
Examples of a method of supplying HC to the filter 20 or the pre-catalyst 21 include adding fuel to exhaust gas. In the fuel addition to the exhaust gas, a fuel addition mechanism for adding fuel (light oil) to the exhaust gas flowing through the exhaust pipe 19 upstream of the pre-catalyst 21 is provided, and the fuel is added from the fuel addition mechanism to the exhaust gas. Thus, the concentration of oxygen in the exhaust gas flowing into the pre-catalyst 21 and the filter 20 can be reduced, and the concentration of HC can be increased.
[0055]
As shown in FIG. 1, the fuel addition mechanism is mounted so that its injection hole faces the inside of the exhaust branch pipe 18, and is opened by a signal from an ECU 35 to be described later to inject fuel. And an additional fuel supply passage 29 for guiding the fuel discharged from the fuel pump 6 to the fuel addition valve 28.
[0056]
In such a fuel addition mechanism, the high-pressure fuel discharged from the fuel pump 6 is applied to the fuel addition valve 28 via the additional fuel supply passage 29. Then, the fuel addition valve 28 opens according to a signal from the ECU 35, and fuel (HC) is injected into the exhaust branch pipe 18.
[0057]
The fuel injected from the fuel addition valve 28 into the exhaust branch pipe 18 raises the concentration of HC in the exhaust gas flowing from the upstream of the exhaust branch pipe 18 and reaches the pre-stage catalyst 21 and the filter 20, where it is oxidized. You. Heat is generated by this oxidation reaction, and the PM deposited on the filter 20 is oxidized and removed by the heat.
[0058]
Thereafter, the fuel addition valve 28 is closed by a signal from the ECU 35, and the addition of fuel into the exhaust branch pipe 18 is stopped.
[0059]
Further, the engine 1 is provided with a crank position sensor 33 that outputs an electric signal corresponding to the rotational position of the crankshaft.
[0060]
The engine 1 configured as described above is provided with an electronic control unit (ECU: Electronic Control Unit) 35 for controlling the engine 1. The ECU 35 is a unit that controls the operating state of the engine 1 according to the operating conditions of the engine 1 and the driver's requirements.
[0061]
Various sensors are connected to the ECU 35 via electric wiring. In addition to the output signals of the various sensors described above, an output signal of an accelerator opening sensor 36 that outputs an electric signal according to the amount of depression of the accelerator pedal by the driver is output. Is to be entered. The engine load can also be obtained from the output signal of the accelerator opening sensor 36.
[0062]
On the other hand, the fuel injection valve 3, the intake throttle actuator 14, the fuel addition valve 28, and the like are connected to the ECU 35 via electric wiring, so that the ECU 35 can control the above-described components.
[0063]
Further, in the present embodiment, the temperature of the exhaust gas can be increased as another means for removing PM.
[0064]
As a method of raising the temperature of the exhaust gas, a sub-injection in which fuel is injected again during an expansion stroke or an exhaust stroke after the main injection from the fuel injection valve 3 in the engine 1 can be exemplified.
[0065]
The reason why the fuel is injected during the expansion stroke or the exhaust stroke is that the exhaust gas temperature can be increased without substantially affecting the engine output. The fuel injected by this sub-injection raises the temperature of exhaust gas discharged from the cylinder 2. The exhaust gas whose temperature has increased reaches the pre-stage catalyst 21 and the filter 20, and can oxidize and remove PM.
[0066]
Further, in the present embodiment, the temperature of the exhaust gas can be increased by delaying the fuel injection timing into the cylinder 2. If the fuel injection timing is delayed more than usual, the amount of energy consumed for the movement of the piston becomes smaller than the fuel injected at the usual timing. As a result, the temperature of the exhaust gas can be increased, and the PM accumulated on the pre-stage catalyst 21 and the filter 20 can be oxidized and removed.
[0067]
As described above, the method of regenerating the filter 20 includes a method of increasing the temperature of exhaust gas by fuel injection from the fuel injection valve 3 and a method of supplying hydrocarbons to exhaust gas by fuel injection from the fuel addition valve 28. , There is. Here, in the method of injecting fuel from the fuel injection valve 3 to increase the temperature of the exhaust gas, the fuel is injected after the piston reaches the top dead center, so that the injected fuel may reach the cylinder wall. is there. As a result, the engine lubricating oil and the fuel are mixed to dilute the engine lubricating oil, or so-called bore flushing in which the lubricating oil attached to the cylinder wall is washed away by the fuel occurs, thereby causing seizure of the piston or the like. There is a fear. Further, when the temperature of the exhaust gas is increased, when the exhaust gas passes through the exhaust branch pipe 18 and the exhaust pipe 19, heat is released into the atmosphere from the wall surfaces of the exhaust branch pipe 18 and the exhaust pipe 19, and the temperature of the exhaust gas is reduced. Will drop. Therefore, a large amount of fuel is consumed in order to raise the temperature of the filter 20, and there is a possibility that fuel efficiency may deteriorate.
[0068]
On the other hand, in the method in which fuel is added to exhaust gas by fuel injection from the fuel addition valve 28, PM is generated by heat generated when fuel is oxidized in the storage reduction type NOx catalyst carried on the filter 20 and the upstream catalyst 21. Oxidized. As described above, since heat is generated by the NOx storage reduction catalyst, PM can be efficiently oxidized in the filter 20.
[0069]
By the way, although the pre-stage catalyst 21 does not have a filter function, as described above, since the end portion is formed in a lattice shape, PM in the exhaust gas easily adheres to the upstream end. It is difficult to oxidize and remove the PM adhering to the upstream end by adding fuel using the fuel addition valve 28. This is because the heat generated on the upstream side of the pre-catalyst 21 due to the addition of the fuel flows to the downstream side together with the exhaust gas, so that the temperature rise at the upstream end of the pre-catalyst 21 becomes slow. As a result, PM may remain without being oxidized on the upstream side of the pre-catalyst 21, particularly on the upstream end.
[0070]
Here, FIG. 3 is a diagram showing the relationship between the temperature of exhaust gas in the pre-stage catalyst and the PM oxidation rate. At a certain temperature or lower, the oxidation rate of PM becomes substantially zero, and PM is hardly removed. On the other hand, at a certain temperature or higher, the oxidation rate of PM increases as the exhaust gas temperature increases, and the amount of PM removed increases. . At a temperature indicated by A, under certain operating conditions, the amount of PM adhering and the amount of oxidation are balanced. If the temperature is lower than this temperature, the amount of PM adhering to the pre-catalyst 21 is reduced by the PM to be oxidized and removed. More than the amount, and PM is deposited. When the temperature is higher than the temperature indicated by A, the amount of oxidized PM is larger than the amount of PM adhering to the pre-catalyst 21, and the PM can be removed. Then, in the fuel addition by the fuel addition valve 28, the PM at the upstream end of the pre-catalyst 21 does not reach the temperature indicated by A, and PM accumulates.
[0071]
On the other hand, when the temperature of the exhaust gas is increased, the temperature at the upstream end of the pre-catalyst 21 is increased, and the PM attached to the upstream end can be removed. Then, as shown in FIG. 3, as the temperature increases, the oxidation rate of PM increases, and the amount of PM removed per unit time increases.
[0072]
Therefore, in the present embodiment, the PM captured by the filter 20 is oxidized by heat generated when the fuel injected from the fuel addition valve 28 reacts with the pre-stage catalyst 21 and the filter 20 (hereinafter, the fuel addition valve 28). PM removal). On the other hand, PM adhering to the upstream end of the pre-catalyst 21 is oxidized by heat generated by burning the fuel injected by the fuel injection valve 3 in the cylinder 2 (hereinafter, referred to as PM removal by the fuel injection valve 3). . Here, since the amount of PM adhering to the upstream end of the pre-stage catalyst 21 is smaller than the amount of PM captured by the filter 20, the PM removal by the fuel injection valve 3 is performed less frequently than the PM removal by the fuel addition valve 28. can do. Thereby, the number of times of dilution of the lubricating oil, bore flushing and the like can be reduced, and seizure of the piston can be suppressed.
[0073]
Here, the temperature of the upstream end of the pre-catalyst 21 is higher when the PM is removed by the fuel injection valve 3 than when the PM is removed by the fuel addition valve 28. Therefore, it is possible to remove the PM attached to the upstream end of the pre-catalyst 21 that cannot be removed when the PM is removed by the fuel addition valve 28 by the PM removal by the fuel injection valve 3.
[0074]
In the present embodiment, for example, the PM removal by the fuel injection valve 3 is performed after the PM removal by the fuel addition valve 28 is performed a predetermined number of times.
[0075]
Here, FIG. 4 shows a time transition of the amount of PM attached to the upstream end of the pre-catalyst 21, the temperature of the exhaust gas flowing into the pre-catalyst 21 (input gas temperature), and the amount of PM deposited on the filter 20. It is a time chart figure. (1) and (2) in FIG. 4 show the PM removal by the fuel addition valve 28, and (3) shows the PM removal by the fuel injection valve 3.
[0076]
In the PM removal by the fuel addition valve 28, the gas input temperature of the pre-stage catalyst 21 is low, and the PM adhering to the upstream end of the pre-stage catalyst 21 hardly decreases. On the other hand, when the PM is removed by the fuel injection valve 3, the gas input temperature of the upstream catalyst 21 becomes higher than when the PM is removed by the fuel addition valve 28, and the PM and the filter adhering to the upstream end of the upstream catalyst 21 are removed. The PM deposited on 20 can be removed at the same time.
[0077]
The removal of the PM deposited on the filter 20 may be performed at predetermined intervals, or may be performed when the amount of PM deposited on the filter 20 reaches a predetermined amount. . The amount of PM captured by the filter 20 may be determined, for example, by attaching a differential pressure sensor 23 for detecting a differential pressure across the filter 20 to an exhaust pipe, and previously measuring an amount of PM according to the detection value of the differential pressure sensor 23, for example. It can be obtained by obtaining in advance. In addition, the amount of PM adhesion according to the operating state of the engine 1 (exhaust temperature, fuel injection amount, engine speed) is obtained in advance through experiments or the like and mapped, and the amount of PM adhesion obtained from this map is integrated to calculate the PM amount. Can be used as the deposition amount. Further, the amount of accumulated PM may be estimated according to the traveling distance or traveling time of the vehicle.
[0078]
In the present embodiment, after the PM removal by the fuel addition valve 28 is performed twice, the PM removal by the fuel injection valve 3 is performed once. The frequency at which the PM is removed by the fuel injection valve 3 may be determined based on the amount of PM adhering to the upstream end of the pre-catalyst 21, which is obtained in advance through experiments or the like.
[0079]
In this manner, the number of times of performing PM removal by the fuel injection valve 3 can be reduced.
[0080]
Further, in the present embodiment, when the amount of PM adhering to the upstream end of the pre-catalyst 21 increases, the PM removal by the fuel injection valve 3 may be performed instead of the PM removal by the fuel addition valve 28. good. Here, for example, by attaching a differential pressure sensor 24 for detecting a differential pressure across the pre-catalyst 21 to the exhaust pipe, a PM amount according to a detection value of the differential pressure sensor 24 is obtained in advance by an experiment or the like. The amount of PM attached to the front catalyst 21 can be determined. Further, the relationship between the PM emission amount, the exhaust gas temperature, and the amount of PM adhering to the pre-stage catalyst 21 according to the operating state is obtained in advance by experiments or the like and mapped, and the map is used to calculate the amount of PM adhering to the pre-stage catalyst 21. You may get. That is, when the high-temperature exhaust gas flows into the pre-catalyst 21, the amount of PM adhering to the upstream end of the pre-catalyst 21 decreases, so that the PM removal interval can be lengthened. Further, the amount of accumulated PM may be estimated according to the traveling distance or traveling time of the vehicle.
[0081]
Further, in a normal engine operating state, the amount of PM adhering to the front-stage catalyst 21 hardly decreases due to a low exhaust gas temperature. However, as shown in FIG. 4, the PM was removed by the fuel addition valve 28. In this case, the amount of PM adhering to the upstream end of the pre-catalyst 21 decreases to some extent. Therefore, the amount of PM deposited at the upstream end of the pre-catalyst 21 may be obtained from the number of times the PM has been removed by the fuel addition valve 28 and the history of the temperature of the exhaust gas flowing into the pre-catalyst 21 at that time. . In a similar manner, the timing at which the PM is removed by the fuel injection valve 3 may be directly obtained.
[0082]
The amount of PM adhering to the upstream end of the pre-catalyst 21 is obtained by previously obtaining the relationship between the engine speed, the fuel injection amount, and the amount of PM adhering to an experiment or the like, and integrating this value. On the other hand, the amount of PM accumulated at the upstream end of the pre-catalyst 21 is determined in advance by an experiment or the like in which the amount of PM reduced per one PM removal by the fuel addition valve 28 is determined in advance by experiment or the like. The number of times of PM removal by the fuel addition valve 28 up to the present time is obtained by multiplying the PM reduction amount per one time. In addition, the relationship between the exhaust gas temperature and the amount of decrease in PM is obtained in advance through experiments or the like, and a map is obtained. Each time PM is removed by the fuel addition valve 28, the temperature of the exhaust gas obtained from the exhaust gas temperature sensor 22 is substituted into the map. Alternatively, the amount of PM reduction obtained by the above may be integrated to obtain the amount of reduction of PM accumulated at the upstream end of the pre-stage catalyst 21.
[0083]
Further, in the present embodiment, regardless of the PM removal by the fuel addition valve 28, the PM removal by the fuel injection valve 3 is immediately performed when the amount of PM attached to the upstream end of the upstream catalyst 21 increases. May be. By doing so, when the amount of PM deposited on the pre-catalyst 21 exceeds the allowable range, the PM can be quickly removed.
[0084]
As described above, according to the present embodiment, normally, PM removed from the filter 20 due to the addition of fuel from the fuel addition valve 28 is removed, and PM attached to the upstream end of the pre-catalyst 21 is removed. Burns the fuel injected by the fuel injection valve 3 in the cylinder 2 to increase the temperature of the exhaust gas. By making the interval of PM removal by the fuel injection valve 3 longer than the interval of PM removal by the fuel addition valve 28, it is possible to reduce the number of times the lubricating oil is diluted and the number of times bore flushing occurs, Can be suppressed.
<Second embodiment>
In the present embodiment, as compared with the first embodiment, the temperature of the exhaust gas flowing into the pre-catalyst 21 during the regeneration of the filter 20 is determined based on the amount of PM attached to the upstream end of the pre-catalyst 21. They differ in points. Note that, in the present embodiment, the basic configuration of the engine and other hardware to which the present invention is applied is the same as that of the first embodiment, and a description thereof will be omitted.
[0085]
Here, it is difficult to remove PM adhering to the upstream end of the pre-catalyst 21 by adding fuel from the fuel addition valve 28, while oxidation of PM deposited on the filter 20 is caused by fuel injection from the fuel injection valve 3. It is possible to increase the temperature of the exhaust gas or to inject the fuel from the fuel addition valve 28, and it is also possible to perform them simultaneously.
[0086]
Therefore, in the present embodiment, the temperature of the exhaust gas flowing into the pre-stage catalyst 21 is increased as the amount of PM attached to the upstream end of the pre-stage catalyst 21 increases when the filter 20 is regenerated. That is, the temperature of exhaust gas is increased by the fuel injection valve 3 while adding fuel from the fuel addition valve 28. This makes it possible to regenerate the pre-catalyst 21 and the filter 20 at the same time. In addition, the temperature rise of the exhaust gas can be minimized.
[0087]
Here, the PM amount adhering to the upstream end of the upstream catalyst 21 has a correlation with the history of the engine speed and the fuel injection amount and the temperature of the exhaust gas flowing into the upstream catalyst 21. That is, when the engine speed is high and the fuel injection amount is large, the amount of PM discharged is large, so that the amount of PM adhering to the upstream end of the upstream catalyst 21 increases. On the other hand, as the temperature of the exhaust gas increases, the amount of PM oxidized and reduced on the upstream end of the pre-catalyst 21 increases. Therefore, the PM amount adhering to the upstream end of the pre-catalyst 21 can be calculated by integrating the PM amount adhering to the upstream end of the pre-catalyst 21 and the decreasing amount. Further, a differential pressure sensor 24 for detecting a differential pressure before and after the front-stage catalyst 21 is attached to the exhaust pipe, and a PM amount according to a detection value of the differential pressure sensor 24 can be determined in advance by an experiment or the like. . Further, the amount of accumulated PM may be estimated according to the traveling distance or traveling time of the vehicle.
[0088]
Then, as the amount of PM adhering to the upstream end of the pre-catalyst 21 increases, the temperature of the exhaust gas during the regeneration of the filter 20 increases. This is because, as shown in FIG. 3 in the first embodiment, the higher the temperature of the exhaust gas, the faster the oxidation rate of PM, and the more the amount of PM removed per unit time. Therefore, even when the regeneration time of the filter 20 is limited, the PM adhering to the upstream end of the pre-catalyst 21 can be oxidized and removed by adjusting the temperature of the exhaust gas.
[0089]
The temperature of the exhaust gas can be adjusted by the amount of the sub-injection or the delay time of the main injection. That is, when raising the temperature of the exhaust gas, the amount of the sub-injection is increased or the delay time of the main injection is lengthened. The amount of the sub-injection and the delay time of the main injection are obtained by mapping the relationship between the rotational speed, the load, and the target exhaust gas temperature by experiment or the like in advance. Further, feedback control of the amount of sub-injection or the delay time of main injection may be performed so that the output signal of the exhaust temperature sensor 22 becomes the target exhaust temperature. Instead of the feedback control based on the output signal of the exhaust temperature sensor 22, the exhaust temperature downstream of the pre-catalyst 21 is detected, and the amount of the sub-injection or the delay time of the main injection is adjusted so that the detected value becomes the target exhaust temperature. May be performed.
[0090]
As described above, according to the present embodiment, when the filter 20 is regenerated, the exhaust gas temperature increases as the amount of PM attached to the upstream end of the pre-catalyst 21 increases. The deposited PM can be removed at the same time. Further, since the height of the exhaust gas temperature can be minimized, dilution of lubricating oil and bore flushing can be minimized, and seizure of the piston and deterioration of fuel efficiency can be suppressed.
[0091]
【The invention's effect】
The exhaust gas purification system for an internal combustion engine according to the present invention can remove deposits at the upstream end of the pre-catalyst while suppressing dilution of lubricating oil and bore flushing of the internal combustion engine.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing both an engine to which an exhaust gas purification system for an internal combustion engine according to a first embodiment is applied and an intake and exhaust system thereof.
FIG. 2 is a sectional view of a filter. FIG. 2A is a diagram showing a cross section in the transverse direction of the filter. FIG. 2B is a diagram showing a vertical cross section of the filter.
FIG. 3 is a diagram showing a relationship between the temperature of exhaust gas in a pre-stage catalyst and a PM oxidation rate.
FIG. 4 is a time chart showing a time transition of the amount of PM attached to the upstream end of the pre-catalyst, the temperature of exhaust gas flowing into the pre-catalyst (input gas temperature), and the amount of PM deposited on the filter.
[Explanation of symbols]
1 engine
1a Crank pulley
1b Exhaust port
2 cylinders
3 Fuel injection valve
4 common rail
5 Fuel supply pipe
6 Fuel pump
6a Pump pulley
7 belt
8 Intake branch pipe
9 Intake pipe
11 Air flow meter
13 Intake throttle valve
14. Intake throttle actuator
15 Centrifugal supercharger
15a Compressor housing
15b Turbine housing
18 Exhaust branch pipe
19 Exhaust pipe
20 Particulate filter
21 Pre-stage catalyst
22 Exhaust gas temperature sensor
28 Fuel addition valve
29 Additional fuel supply path
33 Crank position sensor
35 ECU
36 Accelerator opening sensor

Claims (6)

A catalyst provided in the exhaust passage of the internal combustion engine and having an oxidizing ability,
A particulate filter provided downstream of the oxidizing catalyst and trapping particulate matter in exhaust gas;
Fuel supply means for supplying fuel into the exhaust from upstream of the catalyst having oxidizing ability;
Filter regeneration means for supplying fuel by the fuel supply means and removing particulate matter deposited on the particulate filter,
A first-stage catalyst regenerating means for increasing the temperature of exhaust gas upstream of the oxidizing catalyst to remove deposits deposited on the oxidizing catalyst,
An exhaust gas purification system for an internal combustion engine, comprising: The apparatus further includes a pre-stage catalyst regeneration timing determining unit that determines a timing of removing the deposits deposited on the catalyst having the oxidizing ability. 2. The exhaust gas purifying system for an internal combustion engine according to claim 1, wherein when the particulate matter deposited on the filter is removed by the filter regenerating means, the pre-catalyst regenerating means increases the temperature of the exhaust gas. . 3. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein an interval at which deposits are removed by the first-stage catalyst regeneration unit is longer than an interval at which particulate matter is removed by the filter regeneration unit. A deposit amount estimating means for estimating an amount of deposits deposited on the catalyst having the oxidizing ability, wherein the filter regeneration means removes deposits deposited on the filter; The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 3, wherein the temperature of the exhaust gas is set higher as the amount of the deposit estimated by (1) increases. A deposit amount estimating means for estimating an amount of deposits deposited on the catalyst having the oxidizing ability, wherein the pre-stage catalyst regenerating means is provided when the amount of deposits estimated by the deposit amount estimating means exceeds an allowable range. The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 4, wherein the deposits are removed by the following method. Exhaust temperature detecting means for detecting the temperature of exhaust gas flowing into the catalyst having the oxidizing ability, wherein the deposition amount estimating means has the oxidizing ability as the temperature of the exhaust gas detected by the exhaust temperature detecting means increases. The exhaust gas purification system for an internal combustion engine according to claim 5, wherein it is determined that the amount of deposits deposited on the catalyst is reduced.

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