JPH0621542B2 - Engine exhaust purification device - Google Patents

Description

The present invention relates to a filter for collecting combustible particles such as carbon contained in exhaust gas from a diesel engine or the like for promoting combustion of the combustible particles. The present invention relates to an exhaust emission control device having a mechanism for burning and removing combustible particles captured in a filter by injecting a solution.

(Prior Art) In order to capture combustible particles (particulates) such as carbon contained in the exhaust gas discharged from a diesel engine, a particulate filter as disclosed in, for example, JP-A-56-98519 is conventionally used. An exhaust emission control device using is proposed. In this device, in order to regenerate the filter that has been clogged by the collected combustible particles, fuel for promoting the combustion of the combustible particles is supplied to the filter, and the combustible particles in the filter are burned and removed. There are some that are designed to do. However, even with this method, there is a problem that ignition does not occur when the exhaust temperature is low, and regeneration is not possible when only low / medium load operation is performed. Therefore, the present applicant previously arranged the sponge-like type and wall-flow type particulate filters in Japanese Patent Application No. 60-23368 in this order from the upstream side of the exhaust system so that the upstream side of the sponge-like type filter was arranged. Has proposed a device for injecting a catalyst solution for promoting combustion.

Here, the above wall flow type filter is configured by using partition walls made of a porous material,
Exhaust gas is passed through this partition wall to filter and collect combustible particles in the exhaust gas, and the size of the pores of the porous material can be reduced to the micron unit, so the collection rate of combustible particles can be increased. However, on the other hand, it is necessary to increase the partition wall area so as not to increase the exhaust back pressure. Therefore, the flammable particles adhere to the entire partition wall having a large area, and even if the catalyst component for promoting combustion is injected to this filter, the catalyst component adheres to the entire partition wall, so that the concentration of the catalyst component is low. Therefore, the ignition temperature of combustible particles cannot be lowered sufficiently. On the other hand, the above-mentioned spongy type filter is made of ceramic fibers formed by collecting ceramic fibers into a cotton shape or ceramic foam formed by molding a ceramic into a sponge shape, and has relatively coarse eyes and combustible particles. Are concentrated in the vicinity of the inlet surface of the filter, and when the catalyst component for promoting combustion is injected to the upstream side of this filter, the two catalyst components are also concentrated in the vicinity of the inlet of the filter. Ignition temperature is sufficiently lowered, filter regeneration efficiency (combustible particle combustion removal rate)
Will also be higher. However, since this filter has coarse eyes, the collection rate of the combustible particles is low, and the combustible particles tend to be blown through when the combustible particles are burned.

Therefore, in the case of using a combination of different types of filters having such advantages and disadvantages as in the device disclosed in Japanese Utility Model Application No. 60-23368, the front portion of the upstream spongy type filter is used. Since the combustible particles and the catalyst component can be concentrated and adhered to the filter, the ignition temperature of the combustible particles captured by this filter can be lowered, and the combustion of the particulates is promoted, so that this filter Has the effect of improving the regeneration efficiency. Further, since the combustible fine particles which are not collected by the spongy type filter are collected by the wall flow type filter arranged on the downstream side, the collection rate of the combustible particles in the exhaust gas does not decrease. Moreover, in the wall flow type filter, the exhaust gas that has become hot due to the combustion of the combustible particles in the upstream sponge type filter flows in, so the combustible particles trapped in the wall flow type filter can also be removed by combustion. It has the effect that it can be performed reliably.

(Problems to be Solved by the Invention) As described above, in the purifying device, the catalyst component is not injected when the exhaust gas temperature is sufficiently higher than the ignition temperature of the combustible particles. However, even when the exhaust gas has a high temperature, the injected catalyst component may remain on the filter inlet side or the like. If high-temperature exhaust gas is passed through an atmosphere containing such catalyst, sulfur in the exhaust gas may be oxidized by the catalyst, and a large amount of trioxide ions (SO ₃ ) and sulfuric acid (H ₂ SO ₄ ) may be generated. . If a large amount of these is produced, corrosion may occur in the filter arrangement portion, and they may be released into the atmosphere.

An object of the present invention is to provide an exhaust gas purifying apparatus for an engine that solves the problems of the prior art.

(Means for Solving Problems) Therefore, in the device of the present invention, when the exhaust gas temperature passing through the particulate filter is equal to or higher than a predetermined value, the exhaust gas is bypassed by bypassing the upstream filter on which the catalyst component is injected. I am trying to flush it. That is, the apparatus of the present invention will be described with reference to FIG. 1 showing an embodiment. A spongy filter 31 and a wall flow type filter 31 for collecting combustible particles in exhaust gas from the upstream side of the exhaust passage 6 will be described. Filter 32
However, the solution injecting means 8 for injecting the solution for promoting the combustion of the combustible particles is arranged in the exhaust passage in the vicinity of the upstream side of the spongy type filter 31 arranged in this order, and the solution is injected. A bypass passage 33 that bypasses the spongy type filter 31 and guides the exhaust gas into the exhaust passage upstream of the wall flow type filter is formed in the exhaust passage upstream of the portion to be filled, and Detour control means (15, 34, 35) for guiding the exhaust gas to the bypass passage when the exhaust gas temperature is equal to or higher than a predetermined value is arranged.

Example An example of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows the overall construction of an embodiment of the present invention, in which a swirl chamber type diesel engine 1 comprises a combustion chamber 2 and a swirl chamber 3 communicating with the combustion chamber 2. A fuel injection pump 4 injects fuel into the swirl chamber 3 of the engine 1 through a fuel injection nozzle 5. The fuel injection pump 4 is synchronously driven by the engine 1. Reference numeral 6 denotes an exhaust passage for exhausting exhaust gas discharged from the inside of the combustion chamber 2 of the engine 1 through an exhaust port into the atmosphere. A particulate filter 30 that collects combustible particles containing as a main component is provided. The particulate filter 30 includes an upstream filter 31 formed of a spongy type filter and a downstream filter 32 formed of a honeycomb wall flow type filter.
The exhaust is arranged in this order from the upstream side.

Here, as shown in the figure, a constant interval is formed between the filters 31 and 32. That is, the filter 31 is mounted on the exhaust gas upstream side of the cylinder 31a having an hourglass cross section in the central axis direction, and a half of the cylinder 31a on the exhaust gas downstream side is a void, and the downstream end of this void is the downstream side. It is connected to the filter 32. Further, a large number of communication holes 31b are opened in the circumferential direction on the outer peripheral surface of the cylinder in this void portion. Further, the downstream opening end 33b of the bypass passage 33 is connected to the exhaust passage portion where the communication hole 31b is located,
The upstream opening end 33a of the bypass passage 33 communicates with the exhaust passage portion 6a on the upstream side of the upstream filter 31. A valve body 34 that is rotatable around one end is arranged in the passage portion 6a where the bypass passage 33 is branched. Depending on the position of the valve body 34, an exhaust passage portion that communicates with the upstream filter 31 and the bypass passage 33. Can be selectively opened and closed. The rotation of the valve element 34 is performed by the switch 35. This switch 35 has a housing 35a.
A diaphragm 35d that divides the interior into an atmospheric pressure chamber 35b and a negative pressure chamber 35c, and a spring 35e inserted in the negative pressure chamber,
The diaphragm 35d has a connecting member 35f that converts the reciprocating motion of the diaphragm 35d into a rotational motion of the valve body 34. Can be introduced. Solenoid valve 35
When g is off, atmospheric pressure is introduced into the negative pressure chamber 35c, whereby the valve body 34 is held at the position shown by the solid line in the figure, and the bypass passage 33 is closed. However, when the solenoid valve 35g is turned on, negative pressure is introduced into the negative pressure chamber 35c, the diaphragm 35d moves against the spring force, the valve body 34 is held at the broken line position in the figure, and the exhaust passage side is Is blocked.

Next, an injector 8 for injecting and supplying a catalyst solution for promoting combustion of combustible particles in the exhaust is provided in an exhaust passage portion between the portion where the valve element 34 is arranged and the upstream filter 31. Has been. The injector 8 is arranged in the exhaust passage 6 upstream of the particulate filter 30 with the injection port 8a facing the filter surface. An air pump 9 that supplies air and a pump 11 that supplies the solution from a tank 10 that stores a catalyst solution are connected to the injector 8. The passage between the inlet port of the pump 11 and the tank 10 is connected via an electromagnetic switching valve 12 to a tank 13 that stores a combustion improver such as a hydrocarbon used to assist the combustion of combustible particles. I'm doing it. When the electromagnetic switching valve 12 is off, only the tank 10 side is pump 1
1, the tank 13 communicates with the pump 11 side when it is on. With such a configuration, the catalyst solution or the auxiliary combustion material that has been pumped to the injector 8 by the pump 11 is injected into the exhaust passage by the air jet supplied from the air pump 9. here,
Reference numeral 14 is an electromagnetic on-off valve that opens and closes the injection port 8a of the injector 8, and covers the injection port 8a when the injector 8 is not used,
It is designed to open when used.

Reference numeral 15 is a control unit that controls the drive control of the above-mentioned respective parts, and can be constituted by, for example, a microcomputer. Various signals indicating the operating state of the engine are input to the unit 15. For example, a signal indicating the exhaust temperature is input from the exhaust temperature sensor 16 arranged on the upstream side of the upstream filter 31, and a key signal is input from the key switch 17. Control unit 1
Reference numeral 5 outputs a control signal for drive control of each unit based on the input signal.

FIG. 2 is a flow chart showing the control operation of the part according to the subject matter of the present invention. The operation of this embodiment will be described with reference to this flowchart.

First, in step ST1, clogging detection control is performed. That is, as is known, the filter 30 is based on factors such as engine operating time, mileage, filter back pressure value, filter electrical resistance change state, and fuel consumption.
Is determined. Next, in step ST2, the exhaust temperature Txe. Is read from the exhaust temperature sensor 16. Next, in the above clogging detection control, the filter 3
When the clogging of 0 is detected, the process proceeds from step ST3 to step ST4 along the flow of "YES", holds the solenoid valve 35g in the OFF state, and sets the valve element 34 to the solid line position in the figure, The bypass passage 33 is closed.

When the next exhaust temperature is 350 ° C. or higher, the combustible particles clogged in the filter 30 can be burned only by supplying the catalyst solution. Therefore, steps ST5, ST6, ST7 are performed.
After sequentially executing the above process to inject the catalyst solution, the process jumps from step ST8 to step ST11 to close the on-off valve 14. However, if the exhaust temperature is 220 ° C or higher, 3
If the temperature is lower than 50 ° C, it is impossible to burn the combustible particles only by supplying the catalyst solution.
After T6 and ST7 are sequentially executed to inject the catalyst solution, the process proceeds from step ST8 along the flow of “NO”. That is, steps ST9 and ST10 are sequentially executed to inject a predetermined amount of the auxiliary combustion substance. If the exhaust temperature is lower than 220 ° C., the temperature is too low to burn the combustible particles, so the exhaust temperature is expected to rise.

On the other hand, if clogging has not occurred, step ST
From No. 3 to “NO”, the process proceeds to step ST12, and when the exhaust temperature Txe.
Proceed to 13 to open the bypass 33. As a result, since the high temperature exhaust gas does not pass through the upstream filter 31 side where the catalyst remains, it is possible to prevent the sulfur component in the exhaust gas from being oxidized to generate SO ₃ and H ₂ SO ₄ . However, the exhaust temperature Txe. Is 45
When the temperature is lower than 0 ° C, step ST12 to step S
Proceeding to T14, the bypass passage 33 is closed and a normal exhaust system is formed. That is, the exhaust gas is discharged through the upstream filter 31 and the downstream filter 32 in order.

As described above, in this example, when the exhaust temperature is high at 450 ° C. or higher, the exhaust is bypassed to the upstream filter and directly guided to the downstream filter. It is possible to reliably avoid the adverse effect that sulfur in the exhaust gas is oxidized by passing through the residual catalyst and a large amount of SO ₃ , H ₂ SO _4, etc. is generated. Further, in this example, at a low temperature (less than 350 ° C. in this example) at which the combustible particles cannot be ignited only by the catalyst solution, it is possible to ignite the combustible particles by supplying an auxiliary material. Therefore, regeneration from clogging of the filter can be efficiently performed.

In the above example, the control is switched when the exhaust gas temperature reaches 450 ° C., but this value should be set individually according to the type of catalyst.

(Effects of the Invention) As described above, according to the present invention, the bypass that bypasses the upstream filter to which the catalyst solution for promoting combustion of combustible particles is injected is bypassed and the exhaust gas is directly guided to the downstream filter. A passage is formed, and when the exhaust temperature is high, the exhaust gas is made to flow through this bypass passage, so that the sulfur in the exhaust gas reacts in a large amount in a high temperature atmosphere in the presence of a catalyst, and SO ₃ , H ₂ SO ₄ It is possible to avoid the adverse effect that is generated.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention, and FIG. 2 is a flow chart showing the operation of the apparatus of FIG. 6 ... Exhaust passage, 15 ... Control unit, 16 ... Exhaust temperature sensor, 31 ... Sponge type filter (upstream side filter), 32 ... Wall flow type filter (downstream side filter), 33 ... ... Detour passage, 34 ... Valve body.

Claims (1)

[Claims] 1. An upstream filter and a downstream filter for collecting combustible particles in exhaust gas are arranged in series from an upstream side of an exhaust passage, and the exhaust passage near the upstream side of the upstream filter is provided in the exhaust passage. Solution injection means for injecting a solution that promotes the combustion of combustible particles is arranged, and in the exhaust passage on the upstream side of the portion where the solution is injected, the exhaust gas of the downstream filter is bypassed by bypassing the upstream filter. Exhaust gas purification of an engine, characterized in that a detour passage leading to the upstream side exhaust passage is formed, and further detour control means for guiding the exhaust gas to the detour passage when the exhaust gas temperature is equal to or higher than a predetermined value is arranged. apparatus.