JPH0715241B2 - Exhaust gas purification device for diesel engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device for a diesel engine, and more particularly to a device for treating particulates and odor components discharged from the diesel engine.

[Conventional technology]

Due to incomplete combustion in diesel engines, the exhaust gas contains particulates (unburned hydrocarbon components, etc.) that are sources of black smoke, and odor components (aldehydes, etc.) that are sources of malodor. ing. Therefore, many exhaust emission control devices have been proposed in which a ceramic filter for removing particulates in exhaust gas and a pellet-shaped exhaust odor adsorbent for removing odors are arranged in an engine exhaust system.

By the way, since this filter is clogged with time, the filter must be regenerated at an appropriate time.
Here, the regeneration of the filter is to burn the accumulated particulates. However, when the adsorbent is arranged downstream of the filter, there is a problem that the adsorbent is deteriorated by the particulate combustion heat when the filter is regenerated.

To solve this problem, for example, Japanese Patent Laid-Open No. 62-178708 discloses that when purifying exhaust gas, exhaust gas is made to flow from a filter to an adsorbent to enable particulate collection and odor adsorption, and to regenerate the filter. At times, a backflow regeneration type exhaust purification device has been proposed in which regeneration gas flows from the adsorbent to the filter so that the adsorbent does not deteriorate due to the combustion heat of particulates.

[Problems to be Solved by the Invention]

In the exhaust gas purification device, since the regeneration gas is guided to the filter after passing through the adsorbent during the regeneration of the filter, the abrasion powder (attrition material) of the adsorbent generated by the engine vibration or the like is filtered by the gas flow. If they are carried, the filters may become clogged, obstructing the flow of regenerated gas and the flow of exhaust gas during exhaust gas purification,
Smooth particulate collection is difficult. In view of the above problems, it is an object of the present invention to provide an exhaust gas purification device in which the adsorbent is not thermally deteriorated when the filter is regenerated and the adsorbent wear powder is not guided to the particulate filter.

[Means for Solving the Problems]

According to the present invention for the above purpose, a filter that collects particulates of exhaust gas in order from the exhaust upstream side in the exhaust passage of the diesel engine, and an adsorbent that adsorbs odorous components are arranged, and the exhaust gas forward direction In the device for purifying exhaust gas by the flow of the exhaust gas, an exhaust branching means for branching the exhaust gas introduced to the device into the filter side and the adsorbent side during the filter regeneration, and the regeneration gas through the filter during filter regeneration through the adsorbent. There is also provided an exhaust gas purification device for a diesel engine, which is provided with an adsorbent bypass means for discharging the gas to the outside.

[Action]

Regarding FIGS. 1 and 2 schematically showing each element in response to a claim, when the filter is regenerated, the exhaust branching means has an exhaust upstream side (FIG. 1) or a downstream side (second side) from the filter.
In the figure, the exhaust gas is branched into the filter side and the adsorbent side. Each branched exhaust gas passes through the filter and the adsorbent, but the exhaust gas that passes through the filter is exhausted to the outside without passing through the adsorbent by the adsorbent bypass means, and is thus adsorbed by the particulate combustion heat during filter regeneration. The agent does not deteriorate. Further, since the exhaust gas passing through the adsorbent is discharged to the outside as it is, the adsorbent abrasion powder is not guided to the filter. In the figure, the shaded area indicates a heater that is heated for filter regeneration, and Fig. 1 shows a normal regeneration system in which the exhaust flow direction during particulate collection matches the exhaust flow direction during filter regeneration. 2 is an exhaust purification device of a reverse flow regeneration system in which the exhaust flow directions are opposite between the time of collection and the time of regeneration, and FIG. 2 is an arrangement configuration when the present invention is applied to each device. It is a figure.

[Examples] Hereinafter, the present invention will be described based on illustrated examples.

FIG. 3 shows a backflow regeneration type muffler-integrated trap embodying the exhaust emission control device of the present invention, in which the first casing is used.
The partition 11 is divided into a first expansion chamber 13 and a third expansion chamber 14 by a partition wall 12, and these first and third expansion chambers 13 and 14 are connected to each other by a short pipe 15 provided in the partition wall 12. Second casing 21
Similarly, the partition wall 22 divides the second and fourth expansion chambers 23 and 24 by a partition wall 22, and these second and fourth expansion chambers 23 and 24 are mutually separated by a large number of small holes (louver plates) 25 formed above the partition wall 22. (See FIG. 4). In the first casing 11, the first expansion chamber 13 is located on the side far from the second casing 21, and in the second casing 21, the second expansion chamber 23 is located on the side far from the first casing 11.

An inlet pipe 31 forming a passage for exhaust gas from an engine (not shown) is branched into first and second inlet pipes 32, 33 on the way. The first inlet pipe 32 extends through the second casing 21 and the partition wall 12 of the first casing 11, communicates with the first expansion chamber 13, and the second inlet pipe 33 penetrates the partition wall 22 of the second casing 21. And extends to communicate with the fourth expansion chamber 24. The outlet pipe for guiding the exhaust gas from this muffler to the outside is the first outlet pipe 36 and the second outlet pipe 36.
Consists of an outlet pipe 37. The first outlet pipe 36 is connected to the first casing 11
And the partition wall 22 of the second casing 21, and communicates with the second expansion chamber 23 through a large number of holes 36a formed in the tube end, and the second outlet pipe 37 is a partition wall of the first casing 11. It extends through 12 and communicates with the third expansion chamber 14. The first control valve 41 for branching the exhaust gas that has passed through the inlet pipe 31 into the first and second inlet pipes 32, 33 is provided in the second inlet pipe 33 and includes a rod.
It is connected to the actuator 43 via 42. First control valve
Although 41 normally closes the second inlet pipe 33, it opens the second inlet pipe 33 when the filter is regenerated as described later. The second control valve 46 is provided in the second outlet pipe 37 and is connected to the actuator 51 via the rod 47. Like the first control valve 41, the second control valve 46 normally closes the second outlet pipe 37 and opens the second outlet pipe 37 when the filter is regenerated.

The actuators 43 and 51 have the same structure and are both diaphragm type. The structure of the actuator 51 will be described below. The shell 52 is divided into a constant pressure chamber 54 and a negative pressure chamber 55 by a diaphragm 53, and the diaphragm 53 is a rod.
The second control valve 46 is connected by 47. The constant pressure chamber 54 is always in communication with the atmosphere, and the negative pressure chamber 55 is connected to the negative pressure supply mechanism 61. The negative pressure chamber 55 is provided with a spring 59.

When the atmospheric pressure is introduced into the negative pressure chamber 55, the diaphragm 53 is displaced by the spring 59 toward the constant pressure chamber 54, and the second control valve 46 is closed. On the other hand, when the negative pressure is introduced into the negative pressure chamber 55, the diaphragm 53 compresses the spring 59 and displaces to the negative pressure chamber 55 side, whereby the second control valve 46 opens. This is an actuator that opens and closes the first control valve 41.
The same applies to 43.

The housing 71 of the filter is provided between the first casing 11 and the second casing 21. The openings 72, 73 at both ends of the housing 71 are cylindrical projections 16 formed in the first casing 11.
And the cylindrical projection 26 formed on the second casing 21 respectively, and these contact portions are clamped as shown in FIG.
It is detachably connected by 81. The clamp 81 has two semi-circular fasteners 82 and 83, which are connected by bolts 84 and nuts 85 at flange portions 82a and 83a formed at both ends. The first inlet pipe 32 and the first outlet pipe 36 have joint portions 34 and 38 in the portion between the first and second casings 11 and 21.
4, 38 are also detachably fastened by the clamp 81.

Thus, the housing 71 has the first and second casings 11,2.
The first and second inlet pipes 32, 3 that form a passage connecting 1
3, the first and second casings 11 and 21, the housing 71, and the first and second outlet pipes 36 and 37 constitute a muffler. A filter 74 that collects particulates in the exhaust gas is provided in the housing 71. The electric heater 75 for igniting and burning the particulates on the filter 74 is provided on the second expansion chamber 23 side of the filter 74, that is, the second casing 21 side. The electric heater 75 is connected to the battery 77 via the relay 76, and is energized to generate heat when the amount of collected particulates reaches a certain value, and ignites the particulates. The amount of particulate collection is determined such that the pressure detected by the pressure sensor 78 provided in the third expansion chamber 14 of the first casing 11 is higher than a constant value every time the vehicle travels a predetermined distance (for example, 100 km). When it gets higher, it is judged that it has reached a certain amount.

The second expansion chamber 23 is filled with a pellet-shaped adsorbent 79 that adsorbs the odor component of exhaust gas. Activated carbon is generally known as the odor adsorbent. It is also possible to use an adsorbent obtained by coating a monolithic ceramic cordierite base material with gamma alumina or another adsorbent (sepiolite, zeolite, etc.). Further, an exhaust temperature sensor 80 formed of, for example, a thermocouple is provided inside the fourth expansion chamber 24 in the vicinity of the small hole 25 of the partition wall 22.

During normal particulate collection and odor adsorption, the first and second control valves 41 and 46 close the second inlet pipe 33 and the second outlet pipe 37, respectively, as shown in FIG. Therefore, the exhaust gas flows from the first inlet pipe 32 into the first expansion chamber 13 and then flows into the filter 74 through the third expansion chamber 14 as shown by the arrow in the figure. While passing through the filter 74, the particulates in the exhaust gas are collected by the filter 74. Further, the exhaust gas flows into the fourth expansion chamber 24 after passing through the filter 74, and passes through the small holes 25 of the partition wall 22 to the second expansion chamber.
23 When flowing upwards and flowing downwards, the adsorbent
The odor component in the exhaust gas is adsorbed by 79. The exhaust gas thus purified is discharged into the atmosphere via the first outlet pipe 36 inserted below the second expansion chamber 23. As described above, since the exhaust flow direction in the second expansion chamber 23 is a so-called down flow from the upper side to the lower side, the exhaust gas must always pass through the adsorbent filling portion regardless of the filling height of the adsorbent 79. And thus effective adsorption is achieved.
Also, the exhaust noise is silenced while the exhaust gas passes through the expansion chambers 13, 14, 23, 24.

When the filter 74 is regenerated, the first and second control valves 41 and 46 are
As shown in FIG. 6, the second inlet pipe 33 and the second inlet pipe 33, respectively.
The outlet pipe 36 is opened. Therefore, the exhaust gas flows through the first and second inlet pipes 32 and 33 as shown by the arrows in FIG. 4, and the exhaust gas passing through the first inlet pipe 32 passes from the first expansion chamber 13 to the third expansion chamber 14 2nd outlet pipe 37 that flows in and has low ventilation resistance
Released into the atmosphere. On the other hand, the exhaust gas passing through the second inlet pipe 33 flows into the fourth expansion chamber 24, a part of which is the filter.
74, and the rest flows into the second expansion chamber 23 through the small hole 25, touches the adsorbent 79, and then is discharged from the first outlet pipe 36 into the atmosphere. Therefore, according to this embodiment, the direction of the exhaust gas flowing in the filter 74 is opposite to that at the time of collecting particulates. At this time, the electric heater 75 is energized to generate heat, which causes the particulates on the filter 74 to ignite and burn.

Therefore, in the present device, the flow of the exhaust gas at the time of filter regeneration is branched into a flow passing only the filter 74 and a flow passing only the adsorbent 79 in addition to the flow not passing the filter 74 and the adsorbent 79. The adsorbent 79 deteriorates due to particulate combustion heat during filter regeneration,
Further, various problems that the filter 74 is clogged by the abrasion powder generated between the adsorbents 79 will be solved. That is,
According to the present embodiment, by the muffler structure of the reverse flow regeneration system, the first control valve 41 that opens so as to guide the exhaust gas to the electric heater 75 side of the filter 74 during regeneration, and the second inlet pipe 33. Second, which constitutes exhaust branch means and opens the valve so that the combustion gas after filter regeneration is directly introduced into the atmosphere
The control valve 46 and the second outlet pipe 37 constitute adsorbent bypass means.

Opening and closing of the first and second control valves 41, 46 and electric heater 75
Is energized by an electronic control unit (ECU) 91 equipped with a microcomputer. The ECU 91 includes an input port 92, an output port 93, a memory 94, and a central processing unit (CP
U) 95, which are interconnected by a bus 96. The input port 92 is connected to the pressure sensor 78, the exhaust temperature sensor 80, and an accelerator lever switch and a vehicle speed sensor described later, and the output port 93 is connected to the negative pressure supply mechanisms 61 and 62 and the relay 76, respectively.

FIG. 7 shows a routine for regenerating the filter by the ECU 91 according to the magnitude of the pressure detected by the pressure sensor 78. This routine is interrupted every predetermined time.

In step 101, it is judged whether or not the flag f is set to 1. The flag f indicates that the filter 74 is being reproduced
Is set to 0 and cleared to 0 at the time of normal particulate collection. Therefore, when collecting particulates, the routine proceeds to step 102, where it is judged whether or not the pressure ΔP detected by the pressure sensor 78 is larger than a predetermined target value. When the amount of collected particulates on the filter 74 is relatively small, the pressure ΔP is smaller than the target value, so the following steps 103 to 108 are skipped and this routine ends. On the other hand, when the amount of collected particulates increases and the pressure ΔP reaches the target value, step 103 and the following steps are executed to start the regeneration process of the filter 74.

In step 103, the flag f is set to 1. Next, at step 104, the first and second control valves 41, 46 are opened and the electric heater 75 is energized. As a result, the electric heater 75 generates heat, ignites the particulates on the filter 74, and burns them. Electric heater 75 in step 105
It is determined whether or not 3 minutes have passed since the power was turned on. Immediately after the regeneration of the filter 74 is started, three minutes have not elapsed, so steps 106 to 108 are skipped, and this routine ends.

When the reproduction process starts, in step 103 the flag f
Is set to 1, so this routine
Now you can go directly from step 101 to step 105, step 10
If it is determined that 5 minutes have elapsed in step 5, steps 106 to 108 are executed to end the reproduction process. Step 106
Then, the power supply to the electric heater 75 is cut off, and step 107
Then, the first and second control valves 41 and 46 are closed. Then, in step 108, the flag f is cleared to 0, and this routine ends.

By the way, when the adsorbent 79 reaches its equilibrium adsorption amount, it can no longer adsorb odorous components any more. Therefore, when the adsorbent 79 is in the equilibrium adsorption state, if the vehicle starts to travel, exhaust gas is rapidly introduced, so the deep odor components that have been adsorbed are momentarily released (purged) into the atmosphere and the odor is removed. Ingredients spread around the vehicle, causing discomfort to people and disturbing the surrounding environment.

According to the present embodiment, in order to avoid the problems described above, the odorous component is purged when the vehicle has started running for a while and the vehicle is in the middle or high speed state. FIG. 8 shows a purge prohibition routine that regulates the introduction of exhaust gas into the adsorbent 79 according to the operating conditions of the vehicle, and this routine is performed independently of the filter regeneration routine. Hereinafter, description will be given with reference to FIGS. 8 and 3.

In step 201, it is judged whether or not the purge prohibition flag fa is set to 1. If the exhaust gas is introduced into the adsorbent 79, the flag fa is cleared to 0, and therefore step 202 is executed. . In step 202, it is judged whether or not the equilibrium adsorption flag fb is set to 1. If the adsorbent 79 still has the odor adsorption ability, the flag fb is cleared to 0, and therefore step 203 is executed. In step 203, it is determined whether or not the engine is currently in the idle state based on the outputs from the accelerator lever switch 96 and the vehicle speed sensor 97 which are interlocked with an accelerator pedal (not shown). After that, for example, it is determined whether or not a predetermined time (for example, 30 minutes) expected that the adsorbent 79 is in the equilibrium adsorption state has elapsed, and if the predetermined time has elapsed, the routine proceeds to step 205, The equilibrium adsorption flag Fb is set to 1. Next, at step 206, the current vehicle speed V is read and it is determined whether or not the vehicle has started running. After the adsorbent 79 is in the equilibrium adsorption state (fb = 1), it is determined to be Yes in step 202 at the time of executing the next routine, and the above-mentioned steps are performed.
Steps 203 and 204 are skipped and this step 206 is directly executed. If it is determined in step 206 that the vehicle has started traveling, that is, Yes, the process proceeds to step 207, where the second control valve 46
Immediately open the valve. At this time, since the first control valve 41 is closed, the first and third expansion chambers 13, 1 are connected via the first inlet pipe 32.
The exhaust gas led to 4 is the second outlet pipe 37 with less ventilation resistance.
As a result, the exhaust gas is hardly supplied to the adsorbent 79 by being discharged to the outside of the vehicle through the exhaust gas, and thus purging of the strong odor component from the adsorbent 79 is prohibited. Then, in the following step 208, the purge prohibition flag Fa is set to 1, and the process proceeds to step 209. When the purge prohibition flag fa is set to 1, the next routine is executed, it is determined as Yes in step 201, and steps 202 to 208 are executed.
Skip to and proceed to step 209 in the same manner.
By the way, when the vehicle starts traveling, the purging is prohibited, and then the purging is started when the vehicle speed V reaches a predetermined value, the purging may be immediately performed depending on the acceleration state at the start. Therefore, in the present embodiment, after purging is prohibited, that is, for a predetermined time (for example, 3 minutes) after the flag fa is set,
After passing, the purge is started only when the vehicle V is traveling at a medium-high speed (for example, V> 30 km / h). Therefore, in step 209, it is determined whether or not 3 minutes have elapsed since the purge prohibition flag fa was set, and if it has elapsed, it is determined as Yes, and the routine proceeds to step 210, where the current vehicle speed V is 30 km.
It is determined whether / h or more. Then, only when these two conditions are satisfied, the routine proceeds to step 211, where the second control valve 46 that has been open until then is closed. When the second control valve 46 is closed, the gas that has been discharged to the outside through the second outlet pipe 37 until then is discharged to the filter 74 and the fourth expansion chamber 24.
And is supplied to the adsorbent 79 inside the second expansion chamber 23 via.
Since the temperature of the exhaust gas is higher than that at the time of idling, the equilibrium adsorption amount of the adsorbent 79 becomes small and the odorous components adsorbed by the adsorbent 79 are desorbed (achievement of purging). At this time, when purging the odorous components, it is preferable that the odorous components gradually diffuse into the atmosphere during traveling, and therefore, the actuator 51 of the second control valve 46 and the negative pressure supply mechanism.
A pressure control mechanism 56 as shown in FIG. 9 for delaying the introduction of the atmospheric pressure into the negative pressure chamber 55 when the control valve is closed is preferably provided between the pressure control mechanism 56 and the control valve 61. In FIG. 9, 57 is an orifice and 58 is a check valve, and atmospheric pressure is gradually introduced to the negative pressure chamber 55, and negative pressure is rapidly introduced.

Then, in steps 212 and 213 following step 211, after clearing the respective flags fa and fb which have been set until then, this routine ends. Incidentally, when it is determined to be No in steps 203, 204 and 206 of this routine, which are before and after, however, the purging prohibition condition is not satisfied in any case, so the subsequent steps are skipped and the routine is ended. Also, in the case of No in each of steps 209 and 210, since it is not the condition for executing the purge, the subsequent steps are similarly skipped to return.

By the way, an adsorbent that absorbs odorous components as described above
If a high temperature (for example, 500 ° C. or higher) exhaust gas temperature is continuously supplied to 79 for a long time, the structure of the adsorbent 79 itself may change due to heat, and eventually the adsorption ability may deteriorate. FIG. 10 shows a routine controlled by the ECU 91 in order to protect the adsorbent 79 from the high temperature exhaust gas against the above problems. This routine is performed independently of the filter regeneration routine and the purge prohibition routine.

First, at step 301, it is judged whether or not the flag fc is set to 1. The flag fc is set to 1 while the high temperature exhaust gas is not supplied to the adsorbent 79, and is cleared to 0 when the odorous component is normally adsorbed. Therefore, when the odor is absorbed, the routine proceeds to step 302, where the exhaust gas temperature T detected by the exhaust temperature sensor 80 is a predetermined temperature (for example, 500
C)) is greater than or equal to. If the exhaust gas temperature T is lower than 500 ° C., the adsorbent 79 has not been thermally deteriorated, so the following steps 303 to 307 are skipped and this routine ends. On the other hand, if the exhaust gas temperature T rises and exceeds 500 ° C, step 3
Proceeding to 03, only the second control valve 46 is opened so that the high-temperature exhaust gas that has passed through the first inlet pipe 32 is discharged to the outside from the second outlet pipe 37. That is, in this step, the exhaust gas bypasses the filter 74 and the adsorbent 79, and the adsorbent 79 is protected from the high temperature exhaust gas. In the following step 304, the flag fc is immediately set to 1 and
Start a timer to set the protection time. Next, at step 305, it is determined whether or not a predetermined time (for example, 10 minutes) has elapsed since the second control valve 46 was opened. That is, in the routine after the flag fc has been set in step 304, Yes is determined in step 301, and step 302
In the routine that skips to 304, the magnitude of the elapsed time is determined in step 305. Step 30 like this
By stopping the supply of the exhaust gas to the adsorbent 79 for a predetermined time at 5, the temperature of the adsorbent 79 itself is lowered during that period. If it is determined in step 305 that the predetermined time has elapsed, the process proceeds to step 306, the second control valve 46 is closed, and the exhaust gas supply to the adsorbent 79 is started again. While the exhaust gas is not being supplied, the detection value of the exhaust temperature sensor 79 drops to 500 ° C or lower, so even if the high-temperature exhaust gas of 500 ° C or higher continues to be supplied, the subsequent routine execution Again, it takes some time for the exhaust gas temperature to be detected to be 500 ° C. or higher, so that the small operation of the second control valve 46 from closing to opening is avoided, and the valve itself It does not impair durability. And step
In step 307 following 304, the flag fc is cleared to 0, and this routine ends. Although it goes back and forth, if the answer in step 305 is No, steps 306 and 307 described above are skipped and the routine ends.

As described above, this adsorbent protection routine
Thermal degradation of 79 is avoided and therefore the durability of adsorbent 79 is improved.

〔effect〕

As described above, according to the present invention, when the filter is regenerated, the exhaust gas guided to the device is branched into the filter side and the adsorbent side,
The hot regenerated gas from the filter is released to the outside without passing through the adsorbent, so that the adsorbent is not thermally deteriorated. In addition, by arranging the filter and the adsorbent in order from the exhaust upstream side, the abrasion powder of the adsorbent is not guided to the filter during normal collection and adsorption, and also during filter regeneration, and the filter is clogged. There is no.

[Brief description of drawings]

1 and 2 are diagrams corresponding to the claims of the present invention; FIG. 3 is a sectional view of a muffler-integrated trap as an embodiment of the present invention; and FIG. 4 is a side view of a partition wall taken along line IV-IV in FIG. ; Fifth
6 is a front view showing a clamp; FIG. 6 is a trap cross-sectional view showing an exhaust flow at the time of filter regeneration; FIG. 7 is a flow chart of a filter regeneration routine; FIG. 8 is a flow chart of an odorous component purge prohibition routine; FIG. 10 is a flow chart of an adsorbent protection routine, which is a block diagram of a pressure control mechanism that can be used when purging odorous components. 13 ... 1st expansion chamber, 14 ... 3rd expansion chamber, 23 ... 2nd expansion chamber, 24
... 4th expansion chamber, 32 ... 1st inlet pipe, 33 ... 2nd inlet pipe, 36 ...
1st outlet pipe, 37 ... 2nd outlet pipe, 41 ... 1st control valve, 46 ... 2nd control valve, 74 ... Filter, 79 ... Adsorbent.

Claims (1)

[Claims] 1. A diesel engine has an exhaust passage in which a filter for collecting particulates of exhaust gas and an adsorbent for adsorbing odorous components are arranged in order from the exhaust upstream side, and exhaust gas is purified by a forward flow of exhaust gas. In the device, when the filter is regenerated, an exhaust branching unit that branches the exhaust gas introduced into the device into a filter side and an adsorbent side, and a regeneration gas that passes through the filter during filter regeneration is discharged to the outside without the adsorbent. An exhaust emission control device for a diesel engine, comprising an adsorbent bypass means.