JP3565141B2 - 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]
2. Description of the Related Art Conventionally, in a diesel engine, a particulate filter is disposed in an engine exhaust passage in order to remove fine particles such as soot contained in exhaust gas. Then, the particulate filter once collects the fine particles in the exhaust gas, and removes the fine particles collected on the particulate filter to regenerate the particulate filter.
[0003]
However, the fine particles collected on the particulate filter do not ignite unless they reach a high temperature of about 600 ° C. or higher, whereas the exhaust gas temperature of a diesel engine is usually much lower than 600 ° C. Therefore, it is difficult to ignite the fine particles on the particulate filter with the exhaust gas heat. Therefore, in order to ignite the fine particles collected on the particulate filter even with the exhaust gas heat considerably lower than 600 ° C., the ignition temperature of the fine particles must be lowered.
[0004]
By the way, it is conventionally known that if a catalyst is supported on a particulate filter, the ignition temperature of fine particles can be reduced. Therefore, various particulate filters supporting a catalyst are known.
[0005]
For example, Japanese Patent Publication No. 7-106290 discloses a particulate filter in which a mixture of a platinum group metal and an alkaline earth metal oxide is supported on the particulate filter. The particulate filter disclosed in this publication is capable of igniting fine particles even at a relatively low temperature of approximately 350 ° C. to 400 ° C., and is capable of continuous combustion depending on the operating conditions.
[0006]
[Problems to be solved by the invention]
Thus, although the exhaust gas temperature is usually much lower than 600 ° C., the exhaust gas temperature reaches 350 ° C. to 400 ° C. when the load is high. Therefore, at first glance, it can be seen that a diesel engine to which the particulate filter disclosed in the above publication is applied is capable of igniting and burning fine particles by exhaust gas heat when the engine load becomes high.
[0007]
However, even if the exhaust gas temperature reaches 350 ° C. to 400 ° C., the fine particles may not actually ignite. Further, even if the fine particles are ignited, only a part of the fine particles burn, and a large amount of fine particles remains unburned.
[0008]
When the amount of fine particles contained in the exhaust gas is small, the amount of fine particles adhering to the particulate filter is small. Therefore, at this time, when the exhaust gas temperature changes from 350 ° C to 400 ° C, the fine particles on the particulate filter ignite, Then it burns continuously. However, if the amount of fine particles contained in the exhaust gas is large, before the fine particles adhering to the particulate filter completely burn, another fine particle accumulates on the fine particles, and the fine particles are laminated on the particulate filter. Will be deposited. Then, some of the fine particles that are likely to come into contact with active oxygen burn, but fine particles that are hardly in contact with active oxygen do not burn, and thus a large amount of fine particles remain unburned.
[0009]
Therefore, if the amount of fine particles contained in the exhaust gas increases depending on the operating state of the engine, a large amount of fine particles will continue to accumulate on the particulate filter even if the particulate filter described in the above publication is used.
[0010]
On the other hand, when a large amount of fine particles accumulate on the particulate filter, the fine particles on the filter gradually become difficult to ignite and burn. The cause is probably that the carbon in the fine particles is changed to a hardly combustible substance such as graphite while the fine particles are being deposited.
[0011]
In fact, if a large amount of fine particles continue to accumulate on the particulate filter, the fine particles do not ignite in a low-temperature exhaust gas of 350 ° C. to 400 ° C., and a high temperature of 600 ° C. or more is required to ignite the accumulated fine particles. Exhaust gas is required. However, in a diesel engine, as described above, the exhaust gas temperature does not usually exceed 600 ° C. Therefore, if the particulates continue to deposit on the particulate filter, it becomes difficult to ignite the deposited particulates with the heat of the exhaust gas.
[0012]
On the other hand, even if the exhaust gas temperature can be raised to a high temperature of 600 ° C. or more, and the deposited fine particles ignite, another problem arises in this case. That is, when the fine particles ignite at a high temperature of 600 ° C. or more, the fine particles emit a bright flame and burn. As a result, the temperature of the particulate filter rises to 800 ° C. or more for a long time until the combustion of the fine particles deposited on the particulate filter is completed.
[0013]
As a result, the particulate filter deteriorates early, and the particulate filter must be replaced with a new one early.
Further, when the deposited fine particles burn, the ash, that is, ash, which is a burning residue, is condensed to form a large lump, and the lump clogs the pores of the particulate filter and causes clogging. The number of clogged pores gradually increases over time. Therefore, the pressure loss of the exhaust gas flow in the particulate filter gradually increases, and as a result, the engine output decreases. Therefore, even if this point is taken into consideration, the particulate filter must be replaced with a new one at an early stage.
[0014]
Once such a large amount of fine particles are deposited in a layered manner, various problems as described above occur. Therefore, in consideration of the balance between the amount of the fine particles contained in the exhaust gas and the amount of the fine particles that can be burned on the particulate filter, it is necessary to prevent the fine particles from depositing on the stack.
[0015]
However, if a particulate filter with a catalyst is provided in the exhaust pipe and a continuous combustion process is performed in which exhaust gas purification is entrusted to the operating state of the engine, the above problem cannot always be avoided.
[0016]
Therefore, if the exhaust gas flows alternately from the upstream side and the downstream side of the exhaust flow with respect to the particulate filter of the purification device so that the particulates can be continuously burned as much as possible regardless of the operation condition, Fine particles accumulate on both side surfaces of the particulate filter. In this manner, the amount of the deposited fine particles per unit area can be reduced, and by switching the exhaust gas flow, the deposited fine particles can be disturbed and blown off. Is provided, the fine particles move around the inside, the chance of contact with the active oxygen releasing agent is increased, and the amount of oxidizable fine particles can be increased.
[0017]
However, even in this case, the exhaust gas temperature is not always at the above-mentioned particulate combustible temperature, and a large amount of particulates may be emitted from the diesel engine depending on the operation state. Therefore, in such a case, the fine particles that cannot be eliminated in a short time gradually accumulate on the particulate filter.
[0018]
Then, when the deposition proceeds to some extent, the ability to oxidize the particulates is extremely reduced. If the exhaust gas is passed through the particulate filter as it is, the deposition of the particulates further progresses, and the regeneration of the particulate filter becomes difficult. . For this reason, it is important to regenerate the particulate filter before the particulate filter oxidizing ability of the particulate filter is extremely reduced.
[0019]
However, in the prior art, there is no technique for accurately measuring or estimating the amount of accumulated particulate before the particulate filter oxidizing ability of the particulate filter is extremely reduced.
[0020]
Further, in the particulate filter described in the above publication, when the exhaust gas temperature becomes 350 ° C. or lower, the fine particles do not ignite, so that the fine particles accumulate on the particulate filter. If the amount of the accumulated fine particles is small, the fine particles can be burned even at an exhaust gas temperature of 350 ° C to 400 ° C, but if the amount of the fine particles is large enough to be deposited in a laminating state, the temperature is no longer from 350 ° C to 400 ° C. The particles cannot be ignited, and if they do, they are only some of them. Therefore, most of the deposited fine particles are left unburned.
[0021]
The present invention has been made in view of the above points, and a problem to be solved is to estimate a deposition amount of fine particles on a filter from an amount of desorbed smoke, and the fine particles are deposited on the filter in a stacked state. It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine, which can prevent a situation in which particulates are burned by raising the temperature of exhaust gas to prevent regeneration of a filter.
[0022]
[Means for Solving the Problems]
In order to achieve the above object, an exhaust gas heating apparatus for an internal combustion engine according to the present invention employs the following means.
[0023]
That is, the exhaust gas purifying apparatus for an internal combustion engine of the present invention collects the particulates in the exhaust gas once by a filter arranged in the engine exhaust passage in order to remove the particulates contained in the exhaust gas, and removes the collected particulates. In the exhaust gas purifying apparatus for an internal combustion engine, which oxidizes and removes the filter to regenerate the filter, the filter may be configured such that the amount of particulates discharged from the internal combustion engine per unit time is smaller than the amount of particulates that can be removed by the filter per unit time. A filter that oxidizes and removes the trapped fine particles in a state where no luminous flame is generated when the amount is small; the filter is provided downstream of the filter in the engine exhaust passage, and the concentration of the fine particles contained in the exhaust gas at the installation location; And a particulate concentration sensor for detecting the concentration of the particulate matter. Having an oxide removal facilitating means for facilitating the.
[0024]
Here, an ECU that controls the entire internal combustion engine will be briefly described, and components of the present invention will be described.
The ECU is a digital computer, as is well known, and includes a central processing controller CPU, a read-only memory ROM, a random access memory RAM, a backup RAM, an input port, an output port, and the like, which are interconnected by a bidirectional bus. .
[0025]
The input ports are electrically connected to various sensors attached to the internal combustion engine or the vehicle. When output signals of these various sensors enter the ECU from the input ports, the parameters related to these sensors are temporarily stored in the random access memory RAM. It is memorized.
[0026]
Then, based on these parameters, the CPU performs the necessary arithmetic processing. In executing the arithmetic processing, the CPU stores the parameters stored in the random access memory RAM through the bidirectional bus as necessary. call.
[0027]
As the “filter”, a particulate filter that removes fine particles such as soot contained in exhaust gas is preferable.
The “particle concentration sensor” may be a known smoke sensor, a transmission smoke meter, an opacimeter, or the like, which detects the concentration of particles contained in exhaust gas.
[0028]
Regarding “when the set value is exceeded”, a so-called threshold can be exemplified as an example of the set value. As is well known, the threshold is the minimum value required for a particular process to occur. In the case of the present invention, the fine particles are deposited on the filter at the minimum value of the exhaust smoke concentration required to be deposited on the filter, in other words, the amount of the deposited fine particles continues to increase, and when the amount of the deposited particles exceeds a certain amount, the fine particles are deposited. This is the limit of the amount of fine particles that cannot be removed immediately by oxidation. The exhaust smoke concentration means a ratio of smoke that has flowed downstream of a portion of the engine exhaust passage where a filter is installed, in the exhaust gas (so-called desorption smoke concentration).
[0029]
In such a case, the exhaust smoke concentration varies depending on the type of the internal combustion engine and the type of vehicle on which the internal combustion engine is mounted, but there is a case where the output value of the particulate concentration sensor exceeds, for example, 15% as an instantaneous value.
[0030]
Another example of the case where the set value is exceeded is a case where the average value of the exhaust smoke concentration exceeds a threshold value when the vehicle has traveled for a certain time or distance regardless of the engine operating conditions. Can be
[0031]
An example of the “oxidation removal promoting unit” is an application program stored in the ROM of the ECU and serving as an execution routine for promoting oxidation removal. Specifically, an application program for executing a heating control for raising the temperature of exhaust gas so as to periodically oxidize fine particles collected by the filter by utilizing heat, and an application for operating an electric heating means such as an electric heater. A program can be exemplified.
[0032]
As means for executing the temperature raising control, for example, a fuel injection valve and an intake throttle valve installed in an intake passage are mentioned. The amount of fuel burned in the cylinder is determined by changing the amount of fuel injected from the fuel injection valve and the amount of intake air flowing through the intake passage by controlling the intake throttle valve, and thus the temperature of exhaust gas changes. Since the ROM for storing these programs has the attribute of the ECU, it can be said that the ECU is a means for promoting oxidation and removal.
[0033]
Therefore, it can be said that the oxidation removal promoting means raises the filter temperature.
Further, the filter temperature is measured by temperature detecting means such as a temperature sensor.
[0034]
Further, as another example of the oxidation removal promoting means, a means for reversing the flow of exhaust gas flowing in the filter can be mentioned. Reversing means flowing the exhaust gas from one side of the filter to the filter so that the exhaust gas flows from the opposite side to the other side so that the exhaust gas flows from the other side. The flow of the exhaust gas from one side of the filter and the flow from the other side are respectively referred to as a forward flow and a backward flow for convenience.
[0035]
By reversing the flow of exhaust gas with respect to the filter, fine particles such as soot move around in the base material of the filter, so that oxidation of the fine particles can be promoted and fine particles can be efficiently purified. Become. The means for reversing the direction of the flow of the exhaust gas in this way is referred to as "exhaust flow switching means".
[0036]
The case where this exhaust flow switching means is applied to the present invention will be described below.
That is, in order to remove the fine particles contained in the exhaust gas, the fine particles in the exhaust gas are once collected by a filter arranged in the engine exhaust passage, and the collected fine particles are oxidized and removed to regenerate the filter. In the exhaust gas purifying apparatus for an internal combustion engine, the filter shines the trapped fine particles when the amount of engine exhaust particulates discharged per unit time by the internal combustion engine is smaller than the amount of oxidizable and removable fine particles per unit time by the filter. A filter configured to oxidize and remove in a state in which no flame is generated, wherein the filter is provided downstream of the filter in the engine exhaust passage and detects a concentration of particulates contained in exhaust gas at the installation location; A first flow of exhaust gas flowing from one side to the other side and a second flow of exhaust gas flowing from the other side to the one side. Exhaust flow switching means for alternately switching the flow; and oxidation removal promoting means for promoting the oxidation removal of the fine particles on the filter when the output value of the fine particle concentration sensor exceeds a specific set value. .
[0037]
More specifically, immediately after the operation of the exhaust gas switching means, the fine particles deposited on the filter are easily separated by the flow from the opposite side, and are discharged from the filter at once. Therefore, by detecting the output value of the particle concentration sensor at this time, it is possible to determine how much particles have accumulated on the filter. When the output value of the particle concentration sensor exceeds a set value, the control is performed so that the oxidation accelerating means operates.
[0038]
The “exhaust flow switching means” includes an exhaust switching valve provided in the exhaust passage at a location upstream of a location where the filter is installed, and one side of the exhaust switching valve and the filter, and the exhaust switching valve and the other side. And a control means for performing switching control of the exhaust gas switching valve.
[0039]
The exhaust gas switching valve has a valve body that is operated by a driving device such as an actuator, and is connected to one of the pair of communication paths that connects to the one side of the filter or the filter according to opening and closing of the valve body. The exhaust gas flowing through the exhaust passage toward the filter is decelerated toward the other communication passage connecting the other side of the internal combustion engine with the internal combustion engine, at an appropriate predetermined time, at an appropriate predetermined traveling distance, or the like. This is a valve device that branches in response.
[0040]
The control means is one of various application programs stored in the ROM for implementing various routines for executing control of the internal combustion engine. Further, since the attribute of the ROM for storing the program relating to the control means is in the ECU, the ECU can be said to be the control means.
[0041]
The output port is electrically connected to various operating devices such as the exhaust switching valve, and operates the various operating devices based on output signals of necessary sensors among the various sensors.
[0042]
When the operation of the exhaust switching valve is controlled based on the calculation result of the CPU, the first flow of the exhaust gas flows to one of the pair of communication paths that connects the exhaust switching valve and one side of the filter. Or a second flow of exhaust gas is generated in the other communication path connecting the other side of the exhaust switching valve and the filter.
[0043]
In the present invention having such a configuration, when the accumulation amount of the fine particles is estimated by the fine particle concentration sensor, and the estimated value (the detection value by the fine particle concentration sensor) is a concentration value exceeding the set value, Activate the oxidation removal promotion means. Therefore, the particulates can be burned before the particulates are deposited so that the filter cannot be regenerated, so that a situation in which the particulate filter cannot be regenerated can be avoided.
[0044]
Further, since the exhaust flow switching means also functions as the oxidation removal accelerating means as described above, when the exhaust gas switching means reverses the flow of the exhaust gas flowing through the filter, the value detected by the particulate concentration sensor becomes the threshold. When it is determined that the value exceeds the value, the exhaust gas switching means, which is a component of the exhaust gas flow switching means, is frequently switched to promote the oxidation of the fine particles, and thus the fine particles are efficiently purified to remove the oxidation. The function as the accelerating means may be enhanced. In addition, as described above, as the oxidation removing accelerating means, the promotion of the oxidation removing is performed by executing the application program for executing the temperature raising control or the application program for operating the electric heating means such as the electric heater. You may try.
[0045]
In this way, the oxidizing and removing ability is doubled, and the efficiency is further improved.
Further, according to the present invention, the particulates in the exhaust gas are once collected by a filter arranged in an engine exhaust passage in order to remove the particulates contained in the exhaust gas, and the collected particulates are oxidized and removed. In the exhaust gas purifying apparatus for an internal combustion engine for regenerating the internal combustion engine, the filter includes the trapping unit when the amount of the particulates discharged from the internal combustion engine per unit time is smaller than the amount of the particulates that can be oxidized and removed by the filter per unit time. A filter for oxidizing and removing the collected fine particles without causing a bright flame, wherein the fine particle concentration is provided downstream of the filter in the engine exhaust passage and detects the concentration of fine particles contained in exhaust gas at the installation location. A flow of exhaust gas from one side of the filter to the other side when an output value of the sensor and the particle concentration sensor exceeds a specific set value. Exhaust flow switching means for alternately switching the flow of exhaust gas and the second flow of exhaust gas from the other side to the one side; and the filter when the output value of the particulate concentration sensor exceeds a specific set value. And a bypass means for flowing exhaust gas into the engine exhaust passage in a state where the exhaust gas is bypassed.
[0046]
Also in this case, the output value of the particle concentration sensor is obtained as an instantaneous value or an average value at a predetermined interval of time or distance, and when these values exceed the specific set value, the oxidation removal promoting means is operated. You may.
[0047]
It is preferable to use a part of the engine exhaust passage as the “bypass means”.
The permissible amount by which the filter can continuously oxidize and remove fine particles is determined to some extent.If the permissible amount is exceeded, the accumulation of fine particles increases at a stretch.In such a situation, the exhaust gas is bypassed and the current Prevent the accumulation of more fine particles than are present. While bypassed, oxidation is gradually promoted over time.
[0048]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
<Overview of device configuration>
FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. The present invention can also be applied to a spark ignition type internal combustion engine.
[0049]
Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Denotes an exhaust valve, and 10 denotes an exhaust port.
[0050]
The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a compressor 15 of an exhaust turbocharger 14 via an intake duct 13.
[0051]
A throttle valve 17 driven by a step motor 16 is arranged in the intake duct 13, and a cooling device 18 for cooling intake air flowing through the intake duct 13 is arranged around the intake duct 13. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 18 and cools the intake air by the engine cooling water.
[0052]
On the other hand, the exhaust port 10 is connected to an exhaust turbine 21 of an exhaust turbocharger 14 via an exhaust manifold 19 and an exhaust pipe 20, and an outlet of the exhaust turbine 21 is connected to an exhaust purification device A having a casing 23 having a built-in particulate filter 22. Be linked.
[0053]
The exhaust manifold 19 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter, referred to as EGR) passage 24, and an electrically controlled EGR control valve 25 is disposed in the EGR passage 24.
[0054]
Further, a cooling device 26 for cooling the EGR gas flowing in the EGR passage 24 is disposed around the EGR passage 24. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 26, and the engine cooling water cools the EGR gas.
[0055]
On the other hand, the fuel injection valve 6 is connected to a fuel reservoir, a so-called common rail 27, via a fuel supply pipe 6a.
An electrically controlled variable discharge fuel pump 28 supplies fuel into the common rail 27, and supplies the fuel supplied into the common rail 27 to the fuel injection valve 6 via the fuel supply pipe 6a. A fuel pressure sensor 29 for detecting the fuel pressure in the common rail 27 is attached to the common rail 27, and a fuel pump is provided so that the fuel pressure in the common rail 27 becomes a target fuel pressure based on an output signal of the fuel pressure sensor 29. 28 is controlled.
[0056]
An electronic control unit (hereinafter referred to as “ECU”) 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. ROM (read only memory) 32, RAM (random access memory) 33, CPU (microprocessor) 34, input port 35 and an output port 36.
[0057]
The output signal of the fuel pressure sensor 29 is input to the input port 35 via the corresponding AD converter 37.
Further, the particulate filter 22 is provided with a temperature sensor 39 as temperature detecting means for detecting the internal temperature of the particulate filter 22, and an output signal of the temperature sensor 39 is input to an input port 35 via a corresponding AD converter 37. Is done.
[0058]
A load sensor 41 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 40 (see FIG. 2) is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port via a corresponding AD converter 37. 35 is input. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 30 °.
[0059]
On the other hand, the output port 36 is connected to the fuel injection valve 6, the throttle valve driving step motor 16, the EGR control valve 25, the fuel pump 28, and an actuator 72 described later via a corresponding drive circuit 38.
[0060]
FIG. 2A shows a relationship between the required torque TQ, the depression amount L of the accelerator pedal 40, and the engine speed N. In FIG. 2A, each curve represents an equal torque curve, a curve indicated by TQ = 0 indicates that the torque is zero, and the remaining curves are TQ = a, TQ = b, and TQ. = C, TQ = d indicates that the required torque gradually increases.
[0061]
The required torque TQ shown in FIG. 2A is stored in advance in the ROM 32 in the form of a map as a function of the depression amount L of the accelerator pedal 40 and the engine speed N as shown in FIG. 2B. In the present embodiment, first, a required torque TQ according to the depression amount L of the accelerator pedal 40 and the engine speed N is calculated from the map shown in FIG. 2B, and the fuel injection amount and the like are calculated based on the required torque TQ. calculate.
<Structure of exhaust gas purification device>
As shown in FIGS. 1, 3, and 4, the exhaust purification device A is connected to an exhaust pipe 70 as an engine exhaust passage at the outlet side of the exhaust turbine 21.
[0062]
A first exhaust passage 76 branched from the exhaust pipe 70 and connected to one surface (one side) and the other surface (the other side) of the particulate filter 22 in the casing 23 containing the particulate filter 22. And a second exhaust passage 77.
[0063]
Further, the exhaust pipe 70 discharges the exhaust gas from the branch point of the first exhaust passage 76 and the second exhaust passage 77 without passing through the particulate filter 22, and bypasses the particulate filter 22. It includes a bypass passage 73 as a means.
[0064]
An exhaust switching valve 71 is installed at a branch point between the first exhaust passage 76 and the second exhaust passage 77, that is, at a location on the exhaust pipe 70 upstream of the location where the particulate filter 22 is installed. . The exhaust switching valve 71 includes a valve body 71a driven by an actuator 72, and selects a first exhaust passage 76 in accordance with a position where the valve body 71a moves, from one side of the particulate filter 22 to the other side. A first flow (forward flow) in which exhaust gas flows through the second exhaust passage 77 and a second flow (backflow) in which the second exhaust passage 77 is selected to flow exhaust gas from the other side to the one side of the particulate filter 22. , Alternately.
[0065]
Here, the casing 23 accommodating the particulate filter 22 is disposed so as to be located directly above the exhaust pipe 70 forming the bypass passage 73, and the exhaust pipe 70 is provided on both sides of the casing 23 via the exhaust switching valve 71. The branched first exhaust passage 76 and the second exhaust passage 77 are connected. That is, the first exhaust passage 76 and the second exhaust passage 77 are formed by a pair of connecting lines respectively connecting the one side of the exhaust switching valve 71 and the particulate filter 22 and the other side of the exhaust switching valve 71 and the particulate filter 22. It can be called a passage.
[0066]
A pressure sensor 100 and a smoke sensor 102 are installed in the vicinity of the upstream side and the downstream side of the exhaust gas purification device A in the exhaust pipe 70, respectively. The pressure sensor 100 detects an exhaust pressure on the upstream side of the exhaust gas purification device A, and the smoke sensor 102 detects the concentration of particulates contained in exhaust gas on the downstream side of the exhaust gas purification device A as a particle concentration sensor. It should be noted that a well-known transmission type smoke meter, opacimeter, or the like may be used instead of the smoke sensor 102. Output signals of the pressure sensor 100 and the smoke sensor 102 are input to the input port 35 via the corresponding AD converters 37.
[0067]
The exhaust switching valve 71 indicates the operating state of the engine, such as the filter temperature detected by the temperature sensor 39, the exhaust pressure detected by the pressure sensor 100, and the concentration of fine particles contained in the exhaust gas detected by the smoke sensor 102. The switching is performed so as to generate the first flow or the second flow in the particulate filter 22 according to the output signal. This switching is performed whenever necessary, such as every time the engine decelerates, every predetermined time, or every predetermined traveling distance.
[0068]
The switching by the exhaust switching valve 71 is controlled by the ECU 30.
The particulate filter 22 in the casing 23 has a length in the width direction perpendicular to the length direction longer than the length in the length direction when the passage direction of the exhaust gas is the length direction. With such a configuration, the space for mounting the exhaust gas purification device A, which includes the casing 23 that contains the particulate filter 22, on the vehicle can be reduced.
[0069]
The drive of the actuator 72 is controlled by control means 75 implemented on the CPU 34 of the ECU 30, and is driven by a control signal from the output port 36. Further, the actuator 72 is driven by a negative pressure formed as the internal combustion engine is driven. When the negative pressure is not applied, the valve body 71a is moved to a position (a forward flow position) where the first exhaust passage 76 is selected. When the first negative pressure is applied, the valve body 71a is controlled to the neutral position, and when the second negative pressure stronger than the first negative pressure is applied, the second exhaust passage 77 is selected. The valve body 71a is controlled to the position (backflow position).
[0070]
When the valve body 71a is at a forward flow position indicated by a broken line in FIG. 3, the exhaust switching valve 71 connects the exhaust pipe 70 to the first exhaust passage 76 and connects the second exhaust passage 77 to the bypass passage 73. Therefore, the exhaust gas flows in the order of the exhaust pipe 70 → the first exhaust passage 76 → the particulate filter 22 → the second exhaust passage 77 → the bypass passage 73, and is discharged to the atmosphere.
[0071]
When the valve body 71a is at the reverse flow position shown by the solid line in FIG. 3, the exhaust switching valve 71 connects the exhaust pipe 70 to the second exhaust passage 77 and connects the first exhaust passage 76 to the bypass passage 73. Therefore, the exhaust gas flows in the order of the exhaust pipe 70 → the second exhaust passage 77 → the particulate filter 22 → the first exhaust passage 76 → the bypass passage 73 and is discharged to the atmosphere.
[0072]
When the valve body 71a is in the neutral position parallel to the axis of the exhaust pipe 70, the exhaust gas is discharged from the exhaust pipe 70 through the exhaust pipe 70 because the exhaust switching valve 71 connects the exhaust pipe 70 directly to the bypass passage 73. The gas flows into the bypass passage 73 without passing through the filter 22, and is released to the atmosphere (see FIG. 12).
[0073]
As described above, by switching the valve element 71a, the forward flow and the backward flow are repeated, so that the fine particles such as soot move around in the base material of the particulate filter 22, thereby promoting the oxidation of the fine particles such as soot. Purification can be performed efficiently.
[0074]
A program (not shown) constituting the operation control execution routine of the exhaust gas switching valve 71 is stored in the ROM of the ECU 30. Since the ROM has the attribute of the ECU 30, the ECU 30 to which the program for controlling the operation of the exhaust gas switching valve 71 belongs. Are control means for controlling the switching of the exhaust gas switching valve 71.
[0075]
The exhaust flow switching means includes at least an ECU 30 serving as control means for performing switching control of the exhaust switching valve 71, an exhaust switching valve 71, and a first exhaust passage 76 and a second exhaust passage 77 which are a pair of communication paths. I will say that.
[0076]
<Structure of particulate filter and continuous oxidation of fine particles>
FIG. 5A is an image diagram in the case where exhaust gas flows through the particulate filter 22 from only one direction. The fine particles accumulate only on one surface of the particulate filter and do not move, causing a rise in the pressure loss of the exhaust gas. In addition, it hinders purification of fine particles such as soot.
[0077]
FIG. 5B is an image diagram in the case where exhaust gas is caused to flow through the particulate filter 22 from both directions. Since the fine particles are disturbed in both the forward flow direction and the reverse flow direction on both surfaces of the particulate filter 22, both surfaces of the particulate filter 22 are disturbed. In addition, or around the inside of the base material, the active points of the entire filter base material can be used to promote oxidation of fine particles such as soot, and the accumulation of fine particles in the particulate filter 22 can be further reduced. it can. Therefore, an increase in the pressure loss of the exhaust gas can be avoided.
[0078]
FIG. 6 shows the structure of the particulate filter 22. 6A shows a front view of the particulate filter 22, and FIG. 6B shows a side sectional view of the particulate filter 22. As shown in FIGS. 6A and 6B, the particulate filter 22 has a honeycomb structure, and includes a plurality of exhaust gas passages 50 and an exhaust gas outflow passage 51 extending in parallel with each other. It is a so-called wall flow type provided with:
[0079]
The exhaust passage is constituted by an exhaust gas inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust gas outflow passage 51 whose upstream end is closed by a plug 53. In FIG. 6A, hatched portions indicate plugs 53.
[0080]
Therefore, the exhaust gas inflow passages 50 and the exhaust gas outflow passages 51 are alternately arranged via the thin partition walls 54. In other words, the exhaust gas inflow passages 50 and the exhaust gas outflow passages 51 are each surrounded by four exhaust gas outflow passages 51, and each exhaust gas outflow passage 51 is surrounded by five exhaust gas inflow passages 50. To be arranged.
[0081]
The particulate filter 22 is formed from a porous material such as cordierite, for example. Therefore, the exhaust gas that has flowed into the exhaust gas inflow passage 50 flows through the surrounding partition wall 54 into the adjacent exhaust gas outflow passage 51 as indicated by an arrow in FIG. 6B.
[0082]
In this embodiment, a carrier layer made of, for example, alumina is formed on the peripheral wall surface of each exhaust gas inflow passage 50 and each exhaust gas 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 noble metal catalyst on this carrier, and active oxygen release that takes in oxygen when there is excess oxygen around it and retains oxygen, and releases the retained oxygen in the form of active oxygen when the surrounding oxygen concentration decreases Carrying agent.
[0083]
In this case, in the present embodiment, platinum Pt is used as a noble metal catalyst, and alkali metals such as potassium K, sodium Na, lithium Li, cesium Cs, and rubidium Rb, barium Ba, calcium Ca, and strontium Sr are used as active oxygen releasing agents. At least one selected from the group consisting of alkaline earth metals such as, lanthanum La, rare earths such as yttrium Y, and transition metals.
[0084]
In this case, as the active oxygen releasing agent, it is preferable to use 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.
[0085]
Next, the action of removing particulates in the exhaust gas by the particulate filter 22 will be described by taking as an example a case where platinum Pt and potassium K are carried on a carrier, but other noble metals, alkali metals, alkaline earth metals, rare earths, and transition metals are used. Even when used, there is a similar effect of removing fine particles.
[0086]
In a compression ignition type internal combustion engine as shown in FIG. 1, combustion takes place under excess air, and thus the exhaust gas contains excess air. That is, when the ratio of air and fuel supplied to the intake passage, the combustion chamber 5 and the exhaust passage is referred to as the air-fuel ratio of the exhaust gas, the air-fuel ratio of the exhaust gas in the compression ignition type internal combustion engine as shown in FIG. It has become.
[0087]
Further, since NO is generated in the combustion chamber 5, the exhaust gas contains NO. Further, the fuel contains sulfur S, and this sulfur S reacts with oxygen in the combustion chamber 5 to produce SO.₂  It becomes. Therefore, the exhaust gas contains SO₂  Is included. Thus, excess oxygen, NO and SO₂  Will flow into the exhaust gas inflow passage 50 of the particulate filter 22.
[0088]
FIGS. 7A and 7B schematically show enlarged views of the surface of the carrier layer formed on the inner peripheral surface of the exhaust gas inflow passage 50 and the inner wall surface of the pores in the partition wall 54. 7A and 7B, reference numeral 60 denotes platinum Pt particles, and reference numeral 61 denotes an active oxygen releasing agent containing potassium K.
[0089]
As described above, since the exhaust gas contains a large amount of excess oxygen, when the exhaust gas flows into the exhaust gas inflow passage 50 of the particulate filter 22, as shown in FIG.₂But O₂ ⁻Or O^2-On the surface of platinum Pt.
[0090]
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 of₃ ⁻Is potassium nitrate KNO₃Generate
[0091]
Further, as described above, SO2 is contained in the exhaust gas.₂This 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.
[0092]
Then the generated SO₃Is partially absorbed into the active oxygen releasing agent 61 while being further oxidized on 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 K₂SO₄Generate
[0093]
Further, in the combustion chamber 5, fine particles mainly composed of carbon C are generated, and therefore, these fine particles are contained in the exhaust gas. These fine particles contained in the exhaust gas are generated when the exhaust gas flows in the exhaust gas inflow passage 50 of the particulate filter 22 or when the exhaust gas flows from the exhaust gas inflow passage 50 to the exhaust gas outflow passage 51. In FIG. 7 (B), as indicated by reference numeral 62, it comes into contact with and adheres to the surface of the carrier layer, for example, the surface of the active oxygen releasing agent 61.
[0094]
When the fine particles 62 adhere to the surface of the active oxygen releasing agent 61 as described above, the oxygen concentration at the contact surface between the fine particles 62 and the active oxygen releasing agent 61 decreases. Then, 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 tends to move toward the contact surface between the fine particles 62 and the active oxygen releasing agent 61. I do. 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 fine particles 62 and the active oxygen releasing agent 61, and NO is released from the active oxygen releasing agent 61 to the outside.
[0095]
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.
At this time, the potassium sulfate K formed in the active oxygen releasing agent 61₂SO₄Also potassium K, oxygen O and SO₂Oxygen O moves toward the contact surface between the fine particles 62 and the active oxygen releasing agent 61,₂Is released from the active oxygen releasing agent 61 to the outside.
[0096]
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 stabilized, so potassium nitrate KNO₃Active oxygen is more difficult to release.
[0097]
On the other hand, the oxygen O heading toward the contact surface between the fine particles 62 and the active oxygen releasing agent 61 is potassium nitrate KNO₃  And potassium sulfate K₂SO₄Is oxygen decomposed from such a compound.
[0098]
Oxygen O decomposed from the compound has high energy and extremely high activity. Therefore, the oxygen that goes to the contact surface between the fine particles 62 and the active oxygen releasing agent 61 is active oxygen O. When the active oxygen O comes into contact with the fine particles 62, the fine particles 62 are oxidized within a short period of time without emitting a bright flame, and the fine particles 62 almost disappear. Therefore, the fine particles 62 do not accumulate on the particulate filter 22.
[0099]
When the particulates deposited in a stacked manner on the particulate filter 22 burn as in the prior art, the particulate filter 22 glows red and burns with a flame. Such combustion with a flame cannot be sustained unless it is at a high temperature. Therefore, in order to maintain such combustion with a flame, the temperature of the particulate filter 22 must be maintained at a high temperature.
[0100]
On the other hand, in the present embodiment, the fine particles 62 are oxidized without emitting a bright flame as described above, and the surface of the particulate filter 22 does not glow at this time. That is, in the present invention, the fine particles 62 are oxidized and removed even at a considerably lower temperature than in the prior art.
[0101]
Therefore, the action of removing fine particles 62 that do not emit a luminous flame by oxidation according to the present embodiment is completely different from the action of removing fine particles by conventional combustion involving a flame.
Further, the action of removing fine particles by oxidation of the fine particles is performed at a considerably low temperature. Therefore, the temperature of the particulate filter 22 does not rise so much, and there is almost no risk of the particulate filter 22 being deteriorated. Further, since almost no fine particles are deposited on the particulate filter 22, there is little danger of ash, which is a burning scum of the fine particles, aggregating, and therefore, there is little danger of the particulate filter 22 being clogged.
[0102]
By the way, this clogging is mainly caused by calcium sulfate CaSO₄Caused by That is, the fuel and the lubricating oil contain calcium Ca, and therefore contain calcium Ca in the exhaust gas. This calcium Ca is SO₃In the presence of calcium sulfate CaSO₄Generate This calcium sulfate CaSO₄Is a solid and does not thermally decompose at high temperatures. Therefore, calcium sulfate CaSO₄And this calcium sulfate CaSO₄If the pores of the particulate filter 22 are closed by this, clogging will occur.
[0103]
However, in this case, when an alkali metal or an alkaline earth metal having a higher ionization tendency than calcium Ca, for example, potassium K is used as the active oxygen releasing agent 61, SO diffused into the active oxygen releasing agent 61₃Combines with potassium K to form potassium sulfate K₂SO₄And calcium Ca is SO₃The exhaust gas flows through the partition wall 54 of the particulate filter 22 into the exhaust gas outlet passage 51 without being combined with the exhaust gas.
[0104]
Therefore, the pores of the particulate filter 22 are not clogged. Therefore, as described above, as the active oxygen releasing agent 61, 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 is used. It will be preferable.
[0105]
By the way, the platinum Pt and the active oxygen releasing agent 61 are activated as the temperature of the particulate filter 22 becomes higher, so that the amount of active oxygen O that the active oxygen releasing agent 61 can release per unit time becomes higher when the temperature of the particulate filter 22 becomes higher. It increases indeed. Therefore, the amount of fine particles that can be oxidized and removed by the particulate filter 22 without emitting luminous flame per unit time on the particulate filter 22 (the amount of fine particles that can be oxidized and removed by the particulate filter 22 per unit time; The possible particle amount ") increases as the temperature of the particulate filter 22 increases.
[0106]
FIG. 8 is a graph of the amount G of particulates removable by oxidation and the temperature TF of the particulate filter, in which the vertical axis represents the amount G of particles capable of being removed by oxidation per unit time, and the horizontal axis represents the temperature TF of the particulate filter 22.
[0107]
Assuming that the amount of the particulates discharged from the combustion chamber 5 per unit time is the amount M of the particulates discharged from the engine, an area where the particulates M discharged from the engine is smaller than the particulates G that can be removed by oxidation is indicated by the symbol I, and The operating region in which the number of the oxidizable particles is larger than that of the oxidizable particles G is indicated by II.
[0108]
In the region I of FIG. 8, as soon as all the fine particles discharged from the combustion chamber 5 come into contact with the particulate filter 22, the collected fine particles are oxidized on the particulate filter 22 in a short time without generating a bright flame. It means the operating area to be removed.
[0109]
On the other hand, the region II in FIG. 8 is in an operation region in which the engine discharge particulates M are larger than the oxidation-removable particulates G, that is, when the engine operation is continued in the region II, the particulates are generated due to the shortage of active oxygen. It means the operating area where it is deposited on the stack.
[0110]
FIGS. 9A to 9C show the state of oxidation of the fine particles in the region II in FIG.
That is, in the case where the amount of active oxygen is insufficient to oxidize all the fine particles, when the fine particles 62 adhere to the active oxygen releasing agent 61 as shown in FIG. The fine particles that have not been sufficiently oxidized remain on the carrier layer. Next, when the state of the insufficient amount of active oxygen continues, the fine particles which were not oxidized one after another remain on the carrier layer, and as a result, as shown in FIG. Covered by part 63.
[0111]
The residual fine particle portion 63 covering the surface of the carrier layer is gradually transformed into a carbon material which is hardly oxidized, and therefore, the residual fine particle portion 63 easily remains as it is.
When the surface of the carrier layer is covered with the residual fine particle portion 63, NO, SO₂And the active oxygen releasing agent 61 releases active oxygen. As a result, as shown in FIG. 9C, another fine particle 64 is deposited on the remaining fine particle portion 63 one after another. That is, the fine particles are deposited in a layered manner.
[0112]
When the fine particles are deposited in a stacked manner in this manner, these fine particles are separated from the platinum Pt and the active oxygen releasing agent 61, so that even if they are easily oxidized, they are no longer oxidized by the active oxygen O. Further fine particles are deposited on the fine particles 64 one after another. That is, if the state in which the engine discharge fine particles M are larger than the oxidizable / removable fine particle amount G continues, the fine particles accumulate on the particulate filter 22 in a layered manner.
[0113]
Thus, unless the exhaust gas temperature is raised or the temperature of the particulate filter 22 is raised, the deposited particulates cannot be ignited and burned.
[0114]
In summary, in the region I of FIG. 8, the fine particles are oxidized within a short time without emitting a bright flame on the particulate filter 22, but in the region II of FIG. 8, the fine particles are deposited on the particulate filter 22 in a stacked state. I can say that. In order to prevent the fine particles from depositing on the particulate filter 22 in a stacked state, it is desirable that the amount of the fine particles M discharged from the engine is always smaller than the amount G of the fine particles that can be oxidized and removed.
[0115]
The particulate filter 22 used in the present embodiment can oxidize the fine particles even when the temperature TF is considerably low. Therefore, the engine discharge fine particles M and the temperature TF of the particulate filter 22 can be maintained such that the engine discharge fine particles M become smaller than the oxidizable and removable fine particle amount G. If the operating state is maintained such that the engine discharge fine particles M become smaller than the oxidizable and removable fine particle amount G, the fine particles hardly accumulate on the particulate filter 22.
[0116]
As a result, the pressure loss of the exhaust gas flow in the particulate filter 22 hardly changes. Thus, a decrease in engine output can be kept to a minimum.
In the present embodiment, the engine operation state is basically maintained such that the amount of particulates M discharged from the engine is smaller than the amount G of particulates that can be removed by oxidation in all operation states.
[0117]
However, in practice, it is impossible to make the engine exhaust particulates M smaller than the oxidizable and removable particulate quantity G in all operating states. Therefore, if the engine discharge particulates M become larger than the oxidizable and removable particulates G for some reason, such as a sudden change in the engine operating state, the non-oxidized particulates on the particulate filter 22 begin to remain, and as a result, Fine particles are deposited on the particulate filter 22 in a layered manner.
[0118]
In this case, if the particulates continue to accumulate on the particulate filter 22, it becomes difficult to oxidize and remove the particulates discharged from the engine thereafter on the particulate filter 22. Therefore, in order to continuously oxidize and remove the particulates discharged from the engine on the particulate filter 22, the particulate matter deposited on the particulate filter 22 exceeds the threshold value which is a predetermined limit deposited particulate quantity. A state must be created in which the fine particles are quickly oxidized and removed.
[0119]
However, in practice, it is difficult to determine whether or not the engine discharge fine particles M have become larger than the oxidizable and removable fine particle amount G.
Therefore, in the present embodiment, a smoke sensor 102 as a particle concentration sensor is installed on the downstream side of the exhaust gas purification device A including the particulate filter 22 in the exhaust pipe 70, and at a place where the smoke sensor 102 is installed, particles of the exhaust gas are removed. The density is detected, and when the output value exceeds the threshold value, which is a specific set value, instantaneously or when the output value exceeds an average value during a certain period (predetermined interval) such as an engine operation time or a vehicle mileage, the parameter is set. The oxidization and removal of the fine particles on the particulate filter 22 are promoted to create a state in which the fine particles deposited on the particulate filter 22 are immediately oxidized and removed (see FIGS. 10 and 11). 10 and 11, the vertical axis indicates the desorption smoke concentration and the desorption smoke average concentration, respectively, and the horizontal axis indicates the time. The desorption smoke concentration-time diagram and the desorption smoke concentration- FIG. FIG. 10 shows that the oxidation removal accelerating means is activated when the desorption smoke concentration instantaneously exceeds the threshold value. FIG. 11 shows that when the average concentration of smoke desorbed from the threshold exceeds the threshold, the oxidation removal promoting means is activated. When the oxidation removal promoting means is activated, the temperature of the particulate filter 22 increases.
[0120]
More specifically, if the amount G of particulates that can be removed by oxidation is, for example, in the region II in FIG. 8 depending on the operation state of the engine, the particulates are deposited on the particulate filter 22 in a layered manner and exceed the threshold value. Therefore, the engine control is performed so as to be within the region I in which the amount M of the particulate discharged from the engine is reduced and the amount G of the particulate G that can be removed by oxidation is increased.
[0121]
In order to oxidize and remove the deposited fine particles, the switching valve 71 disposed on the exhaust pipe 70 is switched. When the switching valve 71 is switched, the exhaust upstream side and the exhaust downstream side of the particulate filter 22 are reversed, and the flow of the exhaust gas flowing through the filter is reversed. At the portion of the particulate filter 22 downstream of the exhaust before the switching, the fine particles adhere to the surface of the active oxygen releasing agent 61 to release the active oxygen O, and the fine particles are oxidized and removed.
[0122]
A part of the released active oxygen O moves to the exhaust gas downstream of the particulate filter 22 together with the exhaust gas, and oxidizes and removes fine particles deposited there. Here, as described above, the fine particles are disturbed in the forward flow direction and the reverse flow direction on both surfaces of the particulate filter 22, move around on both surfaces of the particulate filter 22, or inside the base material, and meet the active points of the entire filter base material. Oxidizes and raises filter temperature.
[0123]
By reversing the exhaust upstream and downstream of the particulate filter 22 when the unoxidized particulates begin to accumulate on the particulate filter 22, the particulates can be oxidized and removed from the particulate filter 22.
[0124]
In addition, when the particulates accumulate on the particulate filter 22, the accumulated particulates are oxidized without emitting a bright flame by temporarily making the air-fuel ratio of part or the whole of the exhaust gas rich. When the air-fuel ratio of the exhaust gas becomes rich, that is, when the oxygen concentration in the exhaust gas decreases, active oxygen O is released from the active oxygen releasing agent 61 to the outside at a stretch, and the fine particles deposited by the active oxygen O released at a stretch shine. It is oxidized and removed in a short time without emitting a flame.
[0125]
In this manner, the flow of the exhaust gas flowing through the particulate filter is reversed to promote the oxidization and removal. Therefore, the exhaust gas changeover valve 71 provided in the exhaust pipe 70 at a location upstream of the location where the particulate filter 22 is installed is provided. A first exhaust passage 76 and a second exhaust passage 77 which are a pair of communication passages respectively connecting the exhaust switching valve 71 and the particulate filter 22 to one side and the exhaust switching valve 71 and the other side; It can be said that the exhaust gas purifying apparatus A having the control means 75 for performing the switching control of the above has the exhaust flow switching means and also has the oxidation removal promoting means.
[0126]
When judging from the viewpoint that the oxidation removal promotion means raises the filter temperature as described above, another example of the oxidation removal promotion means is an application program stored in the ROM of the ECU and being an execution routine for promoting the oxidation removal. Can be exemplified.
[0127]
Specifically, an application program for executing a temperature increase control for increasing the temperature of exhaust gas heat and a heating means such as an electric heater for periodically burning the particulate matter collected by the particulate filter by utilizing heat are operated. An application program can be exemplified. Means for executing the temperature increase control include, for example, a fuel injection valve and an intake throttle valve installed in an intake passage. By controlling the amount of fuel injected from the fuel injection valve and the control of the intake throttle valve, the amount of intake air flowing through the intake passage changes to determine the amount of fuel to be burned in the cylinder, and consequently the temperature of exhaust gas changes. Since the ROM for storing these programs has the attribute of the ECU, the ECU can also be referred to as an oxidation removal accelerating means.
[0128]
Hereinafter, an application example of the method of accelerating the removal of fine particles by using the output value of the smoke sensor will be described.
(1) The amount of fine particles deposited on the particulate filter 22 is estimated from the desorbed smoke concentration measured by the smoke sensor and the temperature of the particulate filter 22 and the flow rate of exhaust gas. The regeneration control timing and period of the particulate filter 22 are determined by the temperature raising control means and the exhaust flow switching means. From the temperature of the particulate filter 22 and the flow rate of the exhaust gas, it is possible to roughly determine the amount that can process the fine particles. In addition to this, if the concentration of the desorbed smoke is known, the difference between the two can be determined and the fine particles remaining in the particulate filter 22 can be determined. The amount can be estimated. If the remaining amount is known, it is possible to effectively determine the regeneration control timing and the processing period for the temperature rise control.
(2) PM regeneration when the desorption smoke concentration actually measured by the smoke sensor 102 exceeds an allowable desorption smoke concentration (threshold) corresponding to a change in engine conditions such as a change in exhaust gas flow rate or a change in accelerator opening. Perform processing.
[0129]
By changing the threshold value (comparison value) of the allowable desorption smoke concentration in accordance with the operating conditions at each time, more optimal timing of the PM regeneration processing can be obtained.
(3) The regeneration process is performed when the instantaneous value or average value of the desorbed smoke concentration under certain predetermined operating conditions such as idle exceeds a certain threshold value. In this case, only one threshold value (comparison value) to be compared with the value detected by the smoke sensor needs to be set in advance.
(4) The pressure on the inlet side of the particulate filter 22 is measured by the pressure sensor 100, and the regeneration process is performed when the concentration of the desorbed smoke caused by the instantaneous high-pressure wave exceeds the threshold value of the desorbed amount corresponding to the pressure. I do. Fine particles such as soot have the property of desorbing at a certain pressure, and are used.
(5) When the average amount of desorption smoke in a certain period exceeds the threshold value of the average desorption amount corresponding to the average pressure on the inlet side of the particulate filter 22, the regeneration process is performed. In this case, for example, the average amount of desorption smoke when acceleration or deceleration is performed several times during a certain period is a target.
(6) In the exhaust gas purifying apparatus for an internal combustion engine having the exhaust gas flow switching means, the valve body 71a of the exhaust gas switching valve 71 is switched at certain time intervals under certain predetermined operating conditions such as idling, and the flow direction of the exhaust gas. When the instantaneous value or the average value of the amount of the desorbed fine particles when the flow rate is alternately changed to the forward flow and the reverse flow exceeds a certain threshold value, the regeneration process is performed.
(7) In the case where the desorbed particles in the exhaust gas purifying apparatus A for the internal combustion engine having the exhaust flow switching means are desorbed due to any of the above-described operating states or a combination thereof. The position of the valve body 71a of the exhaust switching valve 71 is set to a neutral state (see FIG. 12), and the exhaust gas is bypassed through the bypass passage 73 to prevent the particulates from accumulating any more. At the same time, a measure for the abnormality of the particulate filter 22 is performed.
[0130]
Here, an example of the abnormality of the particulate filter 22 will be described. The maximum amount that the particulate filter 22 can oxidize the fine particles is determined, but if the fine particles are deposited beyond this maximum amount, the fine particles will self-ignite if no action is taken, There is a possibility that the particulate filter 22 may be melted. Therefore, when there is a possibility that such an abnormal situation may occur, the abnormality is bypassed in advance to prevent the occurrence of the abnormal situation.
(8) In the exhaust gas purifying apparatus for an internal combustion engine having the exhaust flow switching means, for example, when the amount of desorption smoke exceeds a certain threshold during the execution of a steady operation such as an idling operation, the accumulation is performed by executing the engine operation such as rapid acceleration. In an engine operating state in which a large amount of smoke is released at once, the bypass passage 73 is set to the neutral position to suppress the released smoke.
[0131]
Fine particles such as soot are trapped in the particulate filter 22 by the paste-like SOF component in many cases. However, if the exhaust gas temperature rises rapidly due to the operating state of the engine, the SOF component will not burn due to the temperature and the particulates will not be trapped. It is considered that the particles cannot be captured by the curated filter 22, and as a result, separation of the fine particles occurs. In addition, depending on the engine operating conditions, it is conceivable that the flow rate of the exhaust gas is high and the desorption of the fine particles is promoted.
(9) In the exhaust gas purifying apparatus A for an internal combustion engine having the exhaust flow switching means, when the desorption smoke causes particulates to be desorbed due to any of the above-described operating conditions or a combination thereof, the exhaust gas is exhausted. The switching valve 71a is set to an appropriate tilt position (a halfway open state in which the switch valve 71a is not tilted to a neutral position), and only a part of the gas flows to the particulate filter 22 to control the temperature rise. By doing so, the deposited PM is removed and the emission of the desorbed smoke is suppressed.
[0132]
If the particulate filter 22 contains a large amount of fine particles, the oxidation treatment of the particulate filter 22 must be accelerated. Therefore, the oxidation is promoted. However, the amount of the fine particles that enter the particulate filter 22 later is reduced by the oxidation of the particulate filter 22. There may be more than processing capacity. Therefore, in such a case, the valve body 71 a of the exhaust gas switching valve 71 is slightly tilted so that a part of the exhaust gas flows into the bypass passage 73. If particulates accumulate on the particulate filter 22 more than this, if the particulate filter 22 would be hindered from being regenerated, the particulate filter 22 would be neutrally dripped, but if the particulate filter 22 was oxidized to some extent, the exhaust gas was switched. This is because the valve 71a can be handled by slightly inclining the valve 71a.
(10) In the exhaust gas purifying apparatus A for an internal combustion engine having the exhaust flow switching means, desorption smoke causes particulates to be desorbed due to any of the above-described operating conditions or a combination thereof, and furthermore, the temperature of the particulate filter decreases. If the temperature is sufficiently high (300 ° C. or more), the particulates are bypassed by setting the valve body 71 a of the exhaust switching valve 71 to the neutral position for a certain period, and the particulates deposited on the particulate filter 22 are oxidized during that time. After that, the valve body 71a is alternately switched.
(11) In the exhaust gas purifying apparatus A for an internal combustion engine having the exhaust flow switching means, when the desorption smoke causes particles to desorb due to any of the above-described operating states or a combination thereof, By frequently switching the valve body 71a, the oxidation of the fine particles deposited on the particulate filter 22 is promoted. Then, when the amount of desorption smoke falls below a certain threshold value, the valve body 71a is switched alternately. By switching the valve body 71a, vibration is appropriately generated in the particulate filter 22, and as a result, the fine particles search for the active site by themselves, so that oxidation is promoted and this is preferable.
[0133]
If the movement of the valve body 71a is too slow, the amount of bypassed fine particles increases more than necessary. Therefore, it is important to execute the opening and closing speed of the valve body 71a so as to prevent such adverse effects.
[0134]
In the internal combustion engine having such a configuration, the amount of accumulated fine particles is estimated by the smoke sensor 102, and when the estimated value (the value detected by the fine particle concentration sensor) is a concentration value exceeding the threshold value, Activate the oxidation removal accelerating means. Therefore, the particulates can be oxidized before the particulates are deposited so much that the particulate filter cannot be regenerated, thereby avoiding a situation in which the particulate filter cannot be regenerated.
[0135]
Further, by operating the exhaust flow switching means, the particulates attached to the particulate filter 22 can be burned as continuously as possible. That is, since the exhaust gas can be alternately flown from both sides of the particulate filter 22 by providing the exhaust switching valve 71, when the exhaust gas is flown to the particulate filter 22 from only one direction, only one partition surface and only the inside of the partition are oxidized. While the reaction is not used, the amount of fine particles that accumulate in a unit area increases, and the oxidizing performance decreases. On the other hand, in the exhaust gas purifying apparatus for an internal combustion engine of the present embodiment, a forward flow and a backward flow are used alternately. As a result, the exhaust gas flows from both sides of the particulate filter, so that the fine particles are agitated and move around on the partition wall surface and inside the partition wall of the particulate filter, thereby effectively using the catalytic active points on the partition wall surface of the particulate filter and the entire inside of the partition wall. be able to. Therefore, the oxidation of the fine particles can be promoted, the purification can be performed more continuously, and the exhaust gas purification performance can be improved.
[0136]
In this embodiment, the exhaust gas purifying apparatus A employs the exhaust flow switching means and the bypass means, but does not have these means, that is, the particulate filter 22 is formed as a part of the exhaust pipe 70. It is needless to say that an exhaust gas purifying apparatus A having a configuration as shown in a modified example of FIG. 13 in which exhaust gas is directly introduced into the particulate filter 22 may be applied.
[0137]
【The invention's effect】
In the exhaust gas purifying apparatus for an internal combustion engine of the present invention, the amount of particulates deposited on the filter is estimated from the amount of desorbed smoke, and the particulate matter is increased by increasing the exhaust gas temperature before the particulates are deposited on the filter. It is possible to avoid a situation in which the filter burns and the regeneration of the filter becomes impossible.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine to which an exhaust gas purification device for an internal combustion engine of the present invention is applied.
FIG. 2 is a diagram showing a required torque of an engine.
FIG. 3 is a plan view showing an exhaust gas purification device.
FIG. 4 is a side view showing an exhaust gas purification device.
FIG. 5A is an image diagram showing a state in which fine particles are deposited on a filter base material, and FIG. 5B is an image diagram showing a state in which fine particles are disturbed by a forward flow and a backward flow of exhaust gas.
6A is a front view of a particulate filter, and FIG. 6B is a side sectional view of the particulate filter.
FIG. 7 is a conceptual diagram showing an oxidizing action of fine particles.
FIG. 8 is a graph 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 conceptual diagram showing a deposition action of fine particles.
FIG. 10: Desorption smoke concentration-time diagram
FIG. 11: Desorption smoke concentration-time diagram
FIG. 12 is a diagram showing a state where the valve body is at a neutral position parallel to the axis of the exhaust pipe.
FIG. 13 is a diagram showing a modified example of the exhaust emission control device.
[Explanation of symbols]
A Exhaust gas purification device
1 Engine body
2 Cylinder block
3 Cylinder head
4 piston
5 Combustion chamber
6 Electric control type fuel injection valve
6a Fuel supply pipe
7 Intake valve
8 Intake port
9 Exhaust valve
10 Exhaust port
11 Intake branch pipe
12 Surge tank
13 Intake duct
14 Exhaust turbocharger
15 Compressor
16 step motor
17 Throttle valve
18 Cooling device
19 Exhaust manifold
20 exhaust pipe
21 Exhaust turbine
22 Particulate filter (filter)
23 Casing
24 EGR passage
25 Electric control type EGR control valve
26 Cooling device
27 common rail
28 Fuel pump
29 Fuel pressure sensor
30 ECU (oxidation removal accelerating means)
31 Bidirectional bus
32 ROM
33 RAM
34 CPU
35 input port
36 output ports
37 AD converter
38 Drive Circuit
39 Temperature sensor
40 accelerator pedal
41 Load sensor
42 Crank angle sensor
50 Exhaust gas inflow passage
51 Exhaust gas outflow passage
52 stopper
53 stopper
54 partition
60 Platinum Pt particles
61 Active oxygen release agent
62 fine particles
63 Residual fine particle part
64 Another particle
70 exhaust pipe (engine exhaust passage)
71 Exhaust switching valve
71a valve body
72 Actuator
73 Bypass passage (bypass means)
75 Control means
76 First exhaust passage
77 Second exhaust passage
100 pressure sensor
102 Smoke sensor (Particle concentration sensor)
G Amount of fine particles that can be removed by oxidation
L Accelerator pedal depression amount
N engine speed
M Amount of emitted fine particles
O active oxygen
TF Temperature of particulate filter
TQ required torque

Claims (7)

An internal combustion engine that once collects particulates in exhaust gas by a filter disposed in an engine exhaust passage to remove particulates contained in exhaust gas, and oxidizes and removes the collected particulates to regenerate the filter. In the exhaust purification device of
The filter removes the trapped fine particles by oxidation in a state where no luminous flame is generated when the amount of particulates discharged from the internal combustion engine per unit time by the engine is smaller than the amount of fine particles that can be oxidized and removed by the filter per unit time. Filter
A particulate concentration sensor that is installed downstream of the filter in the engine exhaust passage and detects the concentration of particulates contained in exhaust gas at the installation location;
Oxidation removal promoting means for promoting oxidation removal of the particles on the filter when the output value of the particle concentration sensor exceeds a specific set value,
An exhaust gas purification device for an internal combustion engine, comprising: 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said oxidation removal promoting means raises the temperature of the filter. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said oxidation removal promoting means reverses the flow of exhaust gas flowing through the filter. An internal combustion engine that once collects particulates in exhaust gas by a filter disposed in an engine exhaust passage to remove particulates contained in exhaust gas, and oxidizes and removes the collected particulates to regenerate the filter. In the exhaust purification device of
The filter removes the trapped fine particles by oxidation in a state where no luminous flame is generated when the amount of particulates discharged from the internal combustion engine per unit time by the engine is smaller than the amount of fine particles that can be oxidized and removed by the filter per unit time. Filter
A particulate concentration sensor that is installed downstream of the filter in the engine exhaust passage and detects the concentration of particulates contained in exhaust gas at the installation location;
Exhaust flow switching means for alternately switching a first flow of exhaust gas flowing from one side to the other side of the filter and a second flow of exhaust gas flowing from the other side to the one side;
Oxidation removal promotion means for promoting the oxidation removal of the particles on the filter when the output value of the particle concentration sensor exceeds a specific set value,
An exhaust gas purification device for an internal combustion engine, comprising: The output value of the particle concentration sensor is obtained as an instantaneous value or as an average value at a predetermined interval of time or distance, and when these values exceed the specific set value, the oxidation removal promoting means is operated. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1. An internal combustion engine that once collects particulates in exhaust gas by a filter disposed in an engine exhaust passage to remove particulates contained in exhaust gas, and oxidizes and removes the collected particulates to regenerate the filter. In the exhaust purification device of
The filter oxidizes the trapped fine particles without producing a bright flame when the amount of fine particles discharged from the internal combustion engine per unit time is smaller than the amount of fine particles that can be oxidized and removed by the filter per unit time. A filter to remove,
A fine particle concentration sensor installed downstream of the filter in the engine exhaust passage and detecting the concentration of fine particles contained in exhaust gas at the installation location;
A first flow of exhaust gas flowing from one side of the filter to the other side and an exhaust gas flowing from the other side to the one side when the output value of the particle concentration sensor exceeds a specific set value. Exhaust flow switching means for alternately switching the second flow;
Bypass means for flowing exhaust gas to the engine exhaust passage in a state where the filter is bypassed when an output value of the particulate concentration sensor exceeds a specific set value;
An exhaust gas purification device for an internal combustion engine, comprising: The output value of the particle concentration sensor is obtained as an instantaneous value or as an average value at a predetermined interval of time or distance, and when these values exceed the specific set value, the oxidation removal promoting means is operated. An exhaust purification device for an internal combustion engine according to claim 6.

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