JPH07189653A - Exhaust gas purifying method for diesel engine - Google Patents

Abstract

PURPOSE:To realize regeneration of a wash coat layer including no damage by changing combustion condition when a filter on which the wash coat layer is formed so as to carry a catalyst oxide is regenerated, and heating particulates at a high temperature after separating SO2, so as to combustion-eliminate the particulates. CONSTITUTION:Particulates and So2 in exhaust gas are collected in a porous filter 8. When a pressure difference between an inlet side 231 and an outlet 232 is generated in proportion to passing of a time and the pressure difference exceeds a prescribed value, it is detected by a pressure difference sensor 12, a command is given through a valve opening control unit 112 in a central control device 11 so as to throttle an opening degree of an intake throttle valve 20 in an intermediate level. Engine combustion condition is changed so as to raise an exhaust temperature, and SO2 which is adsorbed on a filter 8 is separated. After that, the opening degree of the intake throttle valve 20s is increased in a large level so as to more raise the exhaust temperature. The particulates which are collected on the filter 8 are combustion-eliminated, so that regeneration of the filter 8 may be completed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying exhaust gas of a diesel engine for removing particulates from exhaust gas containing SO ₂ .

[0002]

2. Description of the Related Art Conventionally, as a method of collecting particulates discharged from a diesel engine, a filter provided in the middle of an exhaust pipe and carrying an oxidation catalyst is used. That is, as shown in FIG. 14, the filter 8 is, for example, a porous honeycomb tubular body, and the openings and the closed portions 82 are arranged in a checkered pattern at both ends thereof. And
One opening serves as an exhaust gas inlet 81, and the other serves as an outlet 810.

As shown in FIG. 15, a wash coat layer 84 is provided on the porous cylinder 83 of the filter 8, and the oxidation catalyst 840 is provided on the wash coat layer 84.
Is carried. Platinum, palladium, or the like is used as the oxidation catalyst 840.

Next, as shown by the arrow in FIG. 14, the exhaust gas enters the inside of the filter 8 through the exhaust gas inlet 81, and the wash coat layer 84 and the porous cylinder 83 are introduced.
And discharged from the outlet 810. The particulates 85 contained in the exhaust gas are collected by the wash coat layer 84 and the porous cylinder 83 as they pass through. Therefore, the particulate 85 can be removed from the exhaust gas.

Further, the exhaust gas of a diesel engine is S
It contains O ₂ . The SO ₂ 86 is adsorbed to the filter 8 like the particulate 85. By the way, in the filter 8 which has been used for a long time, the pores of the porous cylinder are closed by the particulates 85 and SO ₂ 86 that have been collected and adsorbed, and exhaust gas becomes difficult to pass. Therefore, it is necessary to periodically heat the filter 8 to burn and remove the collected particulates 85 and SO ₂ 86. The filter 8 is regenerated by the combustion removal.

[0006]

[Problems to be Solved] However, high temperature heating of 450 ° C. or higher is required for burning the particulates.
However, at such high temperature, particulates and S
When the combustion with O ₂ is performed simultaneously, the following problems occur. That is, when the above heating is performed, SO ₂ is emitted due to the above high temperature.
Are oxidized to produce sulfates such as SO ₃ and H ₂ SO ₄ .

Since the above-mentioned sulfate has a strong acidity, the wash coat layer provided on the filter causes a structural change and is damaged. Further, when the heating regeneration is performed with SO ₂ being adsorbed, the light-off temperature (particulate burning temperature) becomes high, and the filter is easily damaged.

Therefore, Japanese Patent Laid-Open No. 61-112716 proposes the following countermeasure method. That is, in the above-mentioned proposed technique, a catalyst that hardly produces sulfate is used in the filter, and a converter to which a catalyst having a low light-off temperature is added is provided upstream of the filter. The heat of combustion reaction in the converter heats and regenerates the filter. However, in the above proposed technology, it is necessary to install a converter before the filter,
The device becomes large and complicated.

In view of the above-mentioned problems, the present invention can be realized by a compact device which does not damage the washcoat layer and can lower the light-off temperature.
It is intended to provide a method for purifying exhaust gas of a diesel engine.

[0010]

In a diesel engine exhaust gas purification method of the present invention, exhaust gas discharged from a diesel engine is passed through a filter having a washcoat layer carrying an oxidation catalyst formed on the surface thereof. An exhaust gas purification method for collecting particulates in the exhaust gas and further regenerating a filter, wherein the SO ₂ adsorbed on the wash coat layer is changed by changing a combustion state in a diesel engine during the regeneration. SO ₂ is desorbed at the first temperature by which S is desorbed, and S
After desorbing O _2, the particulate matter trapped by the filter is burned and removed by setting the second temperature higher than the first temperature to burn off the exhaust gas.

What is most noticeable in the present invention is that the exhaust temperature is set to the first temperature by changing the combustion state of the diesel engine when the filter is regenerated.
SO ₂ desorption is performed, and then the second temperature higher than the first temperature is applied.
It is to raise the temperature and remove the particulates by burning. The wash coat layer of the above filter is
For example, γ-alumina or the like is used. As the oxidation catalyst, for example, palladium, platinum or the like is used.

Next, the first temperature is 350 to 450 ° C.
Is preferred. If the first temperature is higher than 450 ° C, sulfate may be generated. If the above temperature is lower than 350 ℃, SO
₂ may not come off.

Next, the second temperature is 450 ° C. to 600 ° C.
C. is preferred. If the second temperature is higher than 600 ° C., the catalyst may be vaporized and deteriorated due to the high temperature. If the temperature is lower than 450 ° C., the particulates may not burn sufficiently.

Next, the combustion state is changed, for example, by changing the valve opening of the intake throttle valve that introduces air into the diesel engine. The opening degree of the intake throttle valve is set to a medium throttle at the first temperature, and is set to a large throttle that closes larger than the middle throttle at the second temperature.
The intake throttle valve is provided inside an intake pipe connected to the engine. The opening of the valve is determined by, for example, rotating the intake throttle valve so that the cross-sectional area of the intake pipe is 100% when the valve is fully opened.
%), Which is a numerical value (%) showing the degree to which it is narrowed down.

Next, the valve opening at the time of the middle throttle is, for example,
70-80% of full open at medium load and medium speed
Is preferred. When the valve opening is smaller than 70% of the fully opened state, the exhaust gas temperature is too high, so that sulfate may be generated. When the valve opening is greater than 80%, the exhaust temperature is too low, and SO ₂ may not be desorbed.

Next, it is preferable that the valve opening degree at the time of the large throttle is 60 to 70% of the fully opened state. If the valve opening is smaller than 60% of the fully opened state, the engine output may be significantly reduced. If the valve opening is greater than 70%, the exhaust gas temperature is too low, and the particulates may not burn sufficiently.

Next, as a device for realizing the exhaust gas purification method of the diesel engine of the present invention, for example, a differential pressure sensor for detecting a pressure difference between an inlet and an outlet of the filter and a valve opening degree of the intake throttle valve. And a central control unit for controlling SO, and the central control unit receives a signal from the differential pressure sensor to perform SO ₂ desorption with the valve opening degree of the intake throttle valve as an intermediate throttle, and then the valve opening degree. A regeneration command unit that outputs a regeneration command signal of a filter that performs particulate combustion processing with a large throttle and a valve opening control unit that adjusts the valve opening of the intake throttle valve according to a command from the regeneration command unit. There is an exhaust emission control device. According to the above device, it is possible to control the intake throttle valve by using various control devices provided in the conventional vehicle.

Further, the change of the combustion state in the above exhaust gas purification method can be performed by increasing the fuel injection amount when the fuel is supplied to the diesel engine. It is preferable to increase the fuel injection amount by 10% to 20% of the injection amount in the normal combustion state at the first temperature when the engine has a medium load and a medium speed, for example. If the amount of increase is more than 20%, the exhaust gas temperature is too high, which may result in the formation of sulfate. If the amount of increase is less than 10%, the exhaust temperature is too low, and SO ₂ may not be desorbed.

Next, at the second temperature, it is preferable to increase the injection amount by 30% to 40% of the injection amount in the normal combustion state. If the amount of increase is more than 40%, the exhaust gas temperature is too high, which may cause vaporization and deterioration of the catalyst. If the amount of increase is less than 30%, the exhaust gas temperature is too low, and the particulates may not burn sufficiently.

It is also conceivable to change the combustion state by retarding the fuel injection timing when supplying fuel to the diesel engine. Delaying the fuel injection timing means performing combustion injection at an angle before the top dead center of the crank angle. The fuel injection timing is preferably retarded by 3 to 5 degrees from the normal state at the first temperature when the engine has a high load and a low rotation speed. If the retard angle is greater than 5 degrees, the exhaust gas temperature is too high, which may result in the formation of sulfate. If the retard angle is less than 3 degrees, the exhaust temperature is too low and SO ₂ may not be desorbed.

Next, at the second temperature, the retard angle is preferably retarded by 5 to 10 degrees from the normal state.
If the retard angle is greater than 10 degrees, the exhaust gas temperature is too high, which may cause vaporization and deterioration of the catalyst. If the retard angle is less than 5 degrees, the exhaust gas temperature is too low, and the particulates may not burn sufficiently.

Next, as a device for realizing the above exhaust gas purification method, a differential pressure sensor and a central control device are provided, and the central control device receives a signal from the differential pressure sensor and outputs a regeneration command signal. There is an exhaust emission control device that has a regeneration command unit that outputs and a fuel injection control unit that adjusts the fuel injection amount or the retard angle of the fuel injection timing for the fuel injection device according to a command from the regeneration command unit. An example of the fuel injection device is an electronically controlled injection valve.

The above-mentioned device can be realized without adding hardware by changing the program of the engine control device provided in the conventional vehicle. In this case, it is convenient because there is no need to change the design of the vehicle. The exhaust gas purification method by controlling the intake throttle valve and the exhaust gas purification method by controlling the fuel injection amount or the fuel injection timing may be combined. In this case, the degree of freedom in temperature adjustment is greater than in the case of controlling by only a single method.

[0024]

In the method for purifying exhaust gas of a diesel engine of the present invention, first, particulates and SO ₂ in exhaust gas are collected by a filter arranged in the exhaust path. Then, the filter is regenerated to remove the collected particulates and SO ₂ . In performing the regeneration, first, the combustion state of the diesel engine is changed by means such as throttling the intake throttle valve, and the exhaust temperature is set to the first temperature. SO ₂ desorption occurs within a substantially constant temperature range (FIG. 6). The temperature range of the first temperature is not so high that particulate combustion occurs. As a result, SO
Only ₂ can be detached.

After that, the exhaust temperature is raised to a second temperature higher than the first temperature to burn off particulates. When removing the above combustion, SO ₂
Does not remain. Therefore, the formation of sulfate does not occur and the washcoat layer is not damaged. Also, since only particulates are burning, the light-off temperature does not rise. Therefore, the washcoat layer can be further protected. Further, in realizing the present invention, a large-sized device such as the conventionally proposed device shown in the above-mentioned conventional example is not required (FIGS. 1, 8 and 11).

As described above, according to the present invention, the wash-off layer is not damaged, the light-off temperature can be lowered, and it can be realized by a compact device.
An exhaust gas purification method for a diesel engine can be provided.

[0027]

【Example】

Embodiment 1 A diesel engine exhaust gas purification method according to an embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, an exhaust gas purification device 1 used in the exhaust gas purification method of this example.
Is a filter 8, an exhaust pipe 22 for introducing exhaust gas from the diesel engine 2 into the filter 8, an intake pipe 21 for supplying air to the diesel engine 2, and an intake throttle valve arranged in the intake pipe 21. 20 and. In this example, the first temperature and the second temperature are obtained by adjusting the valve opening degree of the intake throttle valve.

The diesel engine 2 includes an intake pipe 2
1, a fuel pipe 290 connected to the fuel tank 29, and an exhaust pipe 22 for exhausting exhaust gas are connected. The filter 8 is housed in the metal casing 23 and is connected to the downstream side of the exhaust pipe 22.

Next, the control system of the above device is shown below. The exhaust gas purification device 1 has a differential pressure sensor 12 for detecting a pressure difference between the inlet side 231 and the outlet side 232 of the filter 8.
And a central control unit 11 for controlling the valve opening degree and the like of the intake throttle valve 20.

The central control unit 11 receives the signal from the differential pressure sensor 12 and outputs a regeneration command signal for the filter 8, and the intake throttle valve 20 according to a command from the regeneration command unit 111. And a valve opening control unit 112 for adjusting the valve opening of the. Furthermore, the central controller 1
1 has an engine control unit 113, which is connected to an accelerator sensor 14 and an engine speed sensor 13 by a signal line. Further, the intake throttle valve 20 is provided with an actuator 15 which operates by receiving an electric signal from the valve opening control section 112.

Next, the function and effect of this example will be described. In performing exhaust gas purification using the exhaust gas purification device 1, first, as shown in FIG. 1, the intake throttle valve 20 is held in a fully open state. At this time, the inside of the diesel engine 2 is maintained in a normal combustion state. The exhaust gas generated from the normal combustion state passes through the exhaust pipe 22 and the filter 8 and is discharged into the atmosphere. At this time, particulates and SO ₂ in the exhaust gas are collected by the porous filter 8 (FIG. 15). Therefore, with the passage of time, these are deposited on the filter 8 and the inlet side 2
A pressure difference is generated between 31 and the outlet side 232.

When the pressure difference reaches a predetermined value, the differential pressure sensor 12 detects it and sends an electric signal to the reproduction command section 111 in the central control unit 11. In response to the above signal, the regeneration command unit 111 instructs the valve opening control unit 112 to
First, a command is issued to set the valve opening of the intake throttle valve 20 to the middle throttle. The valve opening control unit 112 operates the actuator 15 based on the command.

Therefore, as shown in FIG. 2, the actuator 15 changes the valve opening of the intake throttle valve 20 to the middle throttle 201.
State. As a result, the ratio of air to fuel decreases, so the combustion state of the diesel engine 2 changes. In the above combustion state, the exhaust gas temperature rises and the first
Reach the temperature. Therefore, the S adsorbed on the filter 8
O ₂ is released.

After SO ₂ has been desorbed from the filter 8 after a certain period of time has passed, the regeneration command section 111 commands the valve opening control section 112 again. The above-mentioned fixed time is determined in advance by experiments or the like. Based on the above command, the valve opening adjustment unit 112 sets the intake throttle valve 20 to the large throttle 202 as shown in FIG. As a result, the exhaust temperature will be 2
The temperature rises further from 01:00 and reaches the second temperature. Therefore,
The particulates collected by the filter 8 are burned and removed.

Next, the exhaust gas purification and filter regeneration process will be further described with reference to FIG. First, the diagram in Figure 4
(A) shows the valve opening degree, (B) shows the exhaust temperature, (C) shows the SO ₂ adsorption amount in the filter, and (D) shows the time variation of the particulate collection amount in the filter.

As shown in FIG. 4 (A), the exhaust gas purification and filter regeneration processes have two modes.
One is a collection mode (symbol K) that collects and adsorbs particulates and SO ₂ in the exhaust gas, and the other is
This is a reproduction mode (symbol L) for reproducing the filter. The regeneration mode is composed of SO ₂ desorption (reference L1) and particulate combustion (reference L2).

The above two modes change as follows. That is, first, the transition from the collection mode K to the reproduction mode L occurs at time t0. The playback mode is (t1 + t
2) Continue for seconds. In the regeneration mode L, SO ₂ desorption L1 is performed for the first t1 seconds, and particulate combustion L2 is performed for the subsequent t2 seconds. After the end of the reproduction mode L, the mode shifts to the collection mode K again.

Further, the valve opening and the like change as follows with the transition of the above modes. That is, as shown in FIG. 4A, in the collection mode K until time t0, the valve opening is always 100%. At this time, the exhaust temperature is about 250 ° C. as shown in FIG. 4 (B), and the SO ₂ adsorption amount and particulate collection amount continue to increase as shown in FIGS. 4 (C) and (D). ing. That is, it represents a state in which particulates and SO ₂ are being deposited on the filter.

Next, in the SO ₂ desorption L1 which continues for t1 seconds from the time t0 in the regeneration mode L, the valve opening degree is 50.
%, And this state is maintained. At this time, the exhaust temperature rises to 400 ° C. Also, SO ₂ is desorbed from the filter, so the amount of adsorption decreases rapidly (Fig. 4
(C)). Even in this state, the amount of trapped particulates is slightly increased, but the amount of trapped particulates is increased (FIG. 4D).

Next, from the time t0 + t1, the valve opening is 2 in the particulate combustion L2 which continues for t2 seconds.
It is changed to 0% and this state is maintained. At this time, the exhaust temperature rises to about 500 ° C. At this time, the SO ₂ newly flowing into the filter is burned together with the particulates, so the SO ₂ adsorption amount is kept at zero.
Moreover, since the particulates are burned and removed, the amount of trapped particles decreases with time. After time t0 + t1 + t2, the valve opening degree is changed to 100% again, and the mode shifts to the collection mode. Once again, particulates and SO ₂ are collected.

Next, FIG. 5 is a flowchart showing the control procedure of the intake throttle valve performed by the regeneration command in the regeneration mode. That is, in the figure, S (step) 101 indicates a state in which the intake throttle valve is kept fully open and the particulates and SO ₂ are trapped by the filter.

In S102, the regeneration command unit determines whether the value of the differential pressure sensor is equal to or higher than the first set value, that is, the differential pressure required for starting regeneration. When the differential pressure is larger than the first set value, the particulate matter and SO ₂ trapped by the filter increase and the passage of exhaust gas is blocked. In this case, the process proceeds to the next S103.

In S103, the regeneration command unit instructs the valve opening control unit to adjust the valve opening of the intake throttle valve to A% of the middle throttle and hold it for t1 seconds. Therefore, the exhaust temperature is maintained at the first temperature, and SO ₂ is desorbed. After t1 seconds have passed, S10
4, the valve opening is adjusted to A-ΔA% to form a large throttle, so that the exhaust gas temperature is maintained at the second temperature and the particulates are burned and removed.

In S105, the regeneration command unit determines whether or not the value of the differential pressure sensor is equal to or less than the second set value, that is, the differential pressure indicating the end of regeneration. When the differential pressure becomes smaller than the second set value, the particulate and SO ₂
Indicates that it has been removed from the filter. As a result, the reproduction mode L ends and the collection mode K returns again.
The above first and second set values and the like are appropriately determined by experiments and the like.

In this example, the valve opening of the intake throttle valve is adjusted to change the exhaust temperature. That is, in the filter regeneration, it is possible to first desorb SO ₂ and then perform particulate combustion. Therefore, no sulfate is generated and the filter is not damaged by this. Further, at the time of particulate combustion, SO ₂ hardly exists in the filter, so the light-off temperature also becomes low. Also in this respect, it is possible to prevent the filter from being damaged.

Further, the apparatus of this example requires few new parts. Therefore, the device is compact. Therefore, according to this example, it is possible to provide a method for purifying exhaust gas of a diesel engine, which can reduce the light-off temperature without damaging the washcoat layer and can be realized by a compact device.

The apparatus of this embodiment controls the intake throttle valve and the like when the filter is regenerated. The control device may be an engine control device or the like mounted on a conventional vehicle. This point is also superior to the conventional device.

Embodiment 2 As shown in FIGS. 6 and 7, this example shows the relationship between the sulfate generation characteristic and the valve opening and the exhaust temperature. In FIG. 6, the vertical axis represents the sulfate generation characteristic and the horizontal axis represents the exhaust temperature. The figure shows the washcoat layer (γ
-Alumina) is a characteristic of sulfate formation with respect to exhaust temperature when exhaust gas is passed through a filter in which an oxidation catalyst (Pd) is supported. The above-mentioned sulphate production characteristic means that the amount of sulphate production component (mainly SO ₂ etc.) flowing in from the inlet side of the filter is E1, and the amount of sulphate production component (mainly SO ₃ , H ₂ SO ₄ etc.) flowing out from the outlet side is E2. Where, the value of (E2-E1) / E1 is expressed in%.

From the figure, until the exhaust temperature reaches about 350 ° C., the amount of sulfate on the outlet side is smaller than that on the inlet side. This is because SO ₂ is adsorbed on the washcoat layer of the filter. In the temperature range from 350 ° C to 450 ° C, the amount of sulfate from the inlet side to the outlet side slightly increases. This is because the adsorbed SO ₂ is desorbed. On the other hand, when the temperature is higher than 450 ° C, the amount of sulfate on the outlet side increases rapidly. This is because SO ₂ is oxidized by the catalyst and S
This is because it becomes O ₃ , H ₂ SO _4, etc.

Next, in FIG. 7, the vertical axis is the exhaust temperature,
The horizontal axis represents the valve opening. From the figure, it can be seen that it is possible to raise the exhaust temperature by reducing the valve opening, that is, by throttling the intake throttle valve. Therefore, according to this example, it can be understood that SO ₂ desorption and particulate combustion removal can be performed in the filter by controlling the valve opening.

Embodiment 3 As shown in FIGS. 8 and 9, this embodiment is an example in which the combustion state is changed and the filter is regenerated by retarding the fuel injection timing when fuel is supplied to the diesel engine. is there. As shown in FIG. 8, the central control unit 41 of the exhaust emission control device 4 includes a regeneration command unit 411 and a fuel injection control unit 412.
Have and. The fuel injection control unit 412 is connected to the fuel injection device 45 by a signal line. The fuel injection device 45 is provided between the tip of the fuel pipe 290 and the engine 2. Others are the same as in the first embodiment.

FIG. 9 is a flow chart showing the control procedure of the reproduction command section 411 in this example. That is, S20
At 1, the diesel engine is in a normal combustion state, and the injection delay angle of the fuel injection device 45 is 0 degree. At this time, the particulates and SO ₂ are being collected by the filter.

In step S202, the regeneration command unit 411 determines whether the value of the differential pressure sensor 12 is equal to or greater than the first set value, that is, the differential pressure required for starting regeneration. When the differential pressure is larger than the first set value, the process proceeds to next S203. In S203, the fuel injection control unit 412 adjusts the injection delay angle to B degrees with respect to the fuel injection device 45, and t1
Command to hold it for a second. Therefore, the exhaust temperature is maintained at the first temperature, and SO _{2 is} desorbed.

After t1 seconds have passed, the process proceeds to S204,
The fuel injection control unit 412 adjusts the injection delay angle to B + ΔB degrees. Therefore, the exhaust gas temperature is maintained at the second temperature, and the particulates are burned and removed. In step S205, the regeneration command unit 411 again determines whether the value of the differential pressure sensor 12 is equal to or less than the second set value, that is, the differential pressure indicating the end of regeneration. When the differential pressure becomes smaller than the second set value, the particulates and SO ₂ are removed from the filter. As a result, the reproduction mode ends, and the collection mode returns again.

In the purification apparatus of this example, the regeneration command unit 4
Based on the command from 11, the fuel control unit 412 sends a signal for delaying the injection timing to the fuel injection device 45. As a result, the fuel injection timing is retarded from the normal state. Therefore, the mixing ratio of fuel to air increases. As a result, the combustion state of the engine can be changed and the exhaust temperature can be raised. Other than that, the same effects as those of the first embodiment are obtained.

Embodiment 4 As shown in FIG. 10, this embodiment is an example in which the combustion state is changed by increasing the fuel injection amount when fuel is supplied to the diesel engine, and the filter is regenerated.
The device of this example is the same as that of the third embodiment.

FIG. 10 shows a flowchart describing the control procedure of the reproduction command section in this example. That is, S301
In, the diesel engine is in a normal combustion state, and the injection amount of the fuel injection device of the fuel injection device is normal. At this time, the particulates and SO ₂ are being collected by the filter.

In step S302, the regeneration command unit determines whether the value of the differential pressure sensor is equal to or higher than the first set value, that is, whether the differential pressure is required to start regeneration. When the differential pressure is larger than the first set value, the process proceeds to the next S303. S303
In the above, from the fuel injection control unit to the fuel injection device,
The fuel injection amount is increased by C%, and a command to hold this for t1 seconds is issued. Therefore, the exhaust temperature is maintained at the first temperature, and SO _{2 is} desorbed.

After t1 seconds have passed, the process proceeds to S304,
The fuel injection control unit increases the fuel injection amount to C + ΔC%. Therefore, the exhaust gas temperature is maintained at the second temperature, and the particulates are burned and removed. In step S305, the regeneration command unit determines again whether the value of the differential pressure sensor is equal to or less than the second set value, that is, the differential pressure indicating the end of regeneration.
When the differential pressure becomes smaller than the second set value above,
Particulates and SO ₂ have been removed from the filter. As a result, the reproduction mode ends, and the collection mode returns again.

As described above, in the present embodiment, the fuel injection device is instructed to increase the fuel injection amount, and the mixture ratio of fuel to air is increased in two steps to raise the exhaust temperature. In addition, this example has the same effect as that of the third example.

Embodiment 5 In this embodiment, as shown in FIGS. 11 and 12, the valve opening adjustment of the intake throttle valve shown in Embodiment 1 and the fuel injection timing retard adjustment shown in Embodiment 3 are combined. It is a thing. That is, as shown in FIG. 11, the exhaust gas purification device 5 of the present example has an intake throttle valve 20 and a fuel injection device 45, and the central control device 51 has a valve opening device for controlling each of the above devices. The temperature control unit 112, the fuel injection control unit 412, and a regeneration command unit 511 that sends out a regeneration command signal to these. Others are the same as those in the first and third embodiments.

FIG. 12 shows a flowchart describing the control procedure of the reproduction command section 511 in this example. That is, S4
In 01, the diesel engine is in the normal combustion state, the intake throttle valve 20 is in the fully open state, and the fuel injection device 45
The injection retard angle is 0 degree. At this time, the particulates and SO ₂ are being collected by the filter.

In S402, the regeneration command unit 511 determines whether or not the value of the differential pressure sensor 12 is equal to or higher than the first set value, that is, the differential pressure required for starting regeneration. When the differential pressure is larger than the first set value, the process proceeds to next S403. In S403, the fuel injection control unit 412 adjusts the injection delay angle to C degrees with respect to the fuel injection device 45, and t1
Command to hold it for a second. Therefore, the exhaust temperature is maintained at the first temperature, and SO _{2 is} desorbed.

After t1 seconds have passed, the process proceeds to S404,
The valve opening adjustment control unit 112 sends a command to the actuator 15 to adjust the valve opening to D%. Therefore, the exhaust gas temperature is maintained at the second temperature, and the particulates are burned and removed. In step S405, the regeneration command unit 511 determines whether the value of the differential pressure sensor 12 is equal to or less than the second set value, that is, the differential pressure indicating the end of regeneration. When the differential pressure becomes smaller than the second set value, the particulates and SO ₂ are removed from the filter. As a result, the reproduction mode ends, and the collection mode returns again.

In the exhaust gas purification device 5 of this embodiment, the exhaust gas temperature is adjusted by using the intake throttle valve 20 and the fuel injection adjusting device 45, so that the degree of freedom of the exhaust gas temperature increasing method is increased. Others have the same effects as those of the first and third embodiments.

Embodiment 6 As shown in FIG. 13, this embodiment is a combination of the valve opening adjustment of the intake throttle valve shown in Embodiment 1 and the increase of the fuel injection amount shown in Embodiment 4. . The exhaust emission control device of this example is similar to the device of the fifth embodiment.

FIG. 13 shows a flowchart describing the control procedure of the reproduction command section in this example. That is, in S501, the diesel engine is in the normal combustion state, the intake throttle valve is in the fully open state, and the injection amount of the fuel injection device is normal. At this time, particulates and SO ₂
Is being collected by the filter.

In S502, the regeneration command unit determines whether the value of the differential pressure sensor is equal to or higher than the first set value, that is, whether the differential pressure is required for starting regeneration. When the differential pressure is larger than the first set value, the process proceeds to next S503. S503
In the above, from the fuel injection control unit to the fuel injection device,
The injection amount is increased by E%, and a command to hold this for t1 seconds is issued. Therefore, the exhaust temperature is maintained at the first temperature and the SO
₂ Desorption is performed.

After lapse of t1 seconds, the process proceeds to S504,
The valve opening adjustment control unit sends a command to the actuator to adjust the valve opening to F%. Therefore, the exhaust gas temperature is maintained at the second temperature, and the particulates are burned and removed. In step S505, the regeneration command unit again determines whether the value of the differential pressure sensor is equal to or less than the second set value, that is, the differential pressure indicating the end of immediate regeneration. When the differential pressure becomes smaller than the second set value, the particulate and SO
₂ is removed from the filter. As a result, the reproduction mode ends, and the collection mode returns again.

In the exhaust gas purification device of this embodiment, the exhaust gas temperature is adjusted by using the intake throttle valve and the fuel injection amount increasing device, so that the degree of freedom of the exhaust gas temperature increasing method is increased. Others have the same effects as those of the first and fourth embodiments.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an exhaust emission control device for a diesel engine according to a first embodiment.

FIG. 2 is an explanatory diagram showing a valve opening degree during SO ₂ desorption in Embodiment 1.

FIG. 3 is an explanatory view showing a valve opening degree at the time of particulate combustion removal in the first embodiment.

FIG. 4 is a diagram showing a relationship in each mode of the exhaust gas purification method in the first embodiment.

FIG. 5 is a flowchart showing a control procedure of the reproduction command section in the first embodiment.

FIG. 6 is a diagram showing a sulfate generation characteristic in Example 2.

FIG. 7 is a graph showing the relationship between valve opening and exhaust temperature in the second embodiment.

FIG. 8 is an explanatory diagram of an exhaust emission control device for a diesel engine according to a third embodiment.

FIG. 9 is a flowchart showing a control procedure of the reproduction command unit in the third embodiment.

FIG. 10 is a flowchart showing a control procedure of a reproduction command unit in the fourth embodiment.

FIG. 11 is an explanatory diagram of an exhaust emission control device for a diesel engine according to a fifth embodiment.

FIG. 12 is a flowchart showing a control procedure of a reproduction command section in the fifth embodiment.

FIG. 13 is a flowchart showing a control procedure of a reproduction command section in the sixth embodiment.

FIG. 14 is a sectional view of a conventional filter for collecting particulates.

15 is a partially enlarged view showing the adsorption state of SO ₂ and particulates in the filter of FIG.

[Explanation of symbols]

1. ． ． Exhaust gas purification device, 11. ． ． Central controller 111. ． ． Reproduction Command 112. ． ． Valve opening control unit, 12. ． ． Differential pressure sensor, 2. ． ． Diesel engine, 20. ． ． Intake throttle valve, 22. ． ． Exhaust pipe, 412. ． ． Fuel injection control unit, 45. ． ． Fuel injection device, 8. ． ． Filter, 84. ． ． Washcoat layer, 840. ． ． Oxidation catalyst, 85. ． ． Particulate, 86. ． ． SO ₂ ,

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location F02D 41/38 Z 41/40 F 8011-3G D 8011-3G

Claims (5)

[Claims] 1. An exhaust gas discharged from a diesel engine is passed through a filter having a washcoat layer carrying an oxidation catalyst formed on its surface,
An exhaust gas purification method for collecting particulates in the exhaust gas and further regenerating a filter, wherein the SO ₂ adsorbed on the wash coat layer is changed by changing the combustion state in a diesel engine during the regeneration. By setting the first temperature to desorb SO
₂ is desorbed, and after desorption of SO ₂ by the first temperature, a second temperature higher than the first temperature is set to burn and remove the particulates collected by the filter. Diesel engine exhaust purification method featuring. 2. The exhaust gas purification method for a diesel engine according to claim 1, wherein the combustion state is changed by changing a valve opening degree of an intake throttle valve that introduces air into the diesel engine. 3. The valve opening degree of the intake throttle valve according to claim 2, wherein the valve opening degree is a middle throttle at the first temperature and a large throttle that closes larger than the middle throttle at the second temperature. Exhaust purification method for diesel engine. 4. The exhaust gas purification method for a diesel engine according to claim 1, wherein the change of the combustion state is performed by increasing a fuel injection amount when fuel is supplied to the diesel engine. 5. The exhaust gas purification method for a diesel engine according to claim 1, wherein the change of the combustion state is performed by retarding a fuel injection timing when fuel is supplied to the diesel engine.