JPH0623533B2 - Exhaust gas purification device for diesel engine - Google Patents

Description

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

(Prior Art) In order to capture combustible particles (particulates) such as carbon contained in exhaust gas discharged from a diesel engine, conventionally, for example, as disclosed in JP-A-56-98519, An exhaust purification device using a filter has been 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 applicant of the present application has previously disclosed, in Japanese Patent Application No. 60-23368, sponge-like type and wall-flow type particulate filters arranged in this order from the upstream side of the exhaust system, and the upstream side of the sponge-like type filter. A device is proposed in which a catalyst solution for promoting combustion is injected to the side.

(Problems to be Solved by the Invention) Here, in the diesel engine, the intake air supply rate to the combustion chamber is constant, and the fuel supply rate changes according to the change in the load. Therefore, at high load with high fuel supply rate,
The excess air ratio decreases, and as a result, the oxygen concentration in the exhaust gas also decreases. Therefore, when the load is high, there is a possibility that not enough oxygen remains in the exhaust gas to burn the combustible particles collected in the filter. In particular, in the downstream filter, the exhaust gas after burning the combustible particles in the upstream filter flows in, so there is a high risk of such oxygen deficiency. When such a situation occurs, the combustible particles in the filter are incompletely burned, the filter cannot be promptly regenerated from clogging, and a large amount of CO and the like is generated and released into the atmosphere as it is. .

Further, in order to eliminate the oxygen deficiency, when air or oxygen is simply supplied to the upstream side of the upstream filter, the catalyst remaining in the upstream filter accelerates the oxidation of the sulfur component in the exhaust gas, and harmful components such as SO ₃ are generated. A large amount will be discharged.

An object of the present invention is to provide an exhaust emission control device for a diesel engine that solves the problems of the conventional art.

(Means for Solving the Problems) Therefore, in the present invention, the lack of oxygen in the exhaust gas is detected, and when such an oxygen deficiency occurs, oxygen is not provided between the upstream filter and the downstream filter. Is supplied to completely combust combustible particles in the filter and to minimize generation of SO _{3 and the} like.

The configuration of the device 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 32 for collecting combustible particles in exhaust gas are provided in the exhaust passage 6. The filter means 30 arranged in this order from the upstream side, and the catalyst supply means (8, 8a, 10) for supplying the catalyst component for lowering the ignition temperature of the combustible particles to the upstream side of the spongy type filter 31. 1
1, 12, 41) and detection means (41, 44) for detecting whether or not the oxygen in the exhaust passage 6 is sufficient to burn the combustible particles trapped in the filter means 30.
Oxygen supply means (9, 16, 17, 18) for supplying oxygen to the space 6a between the spongy type filter 31 and the wall flow type filter 32 when oxygen is insufficient based on the detection result of the detection means. , 41) and are provided.

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.

In the exhaust passage portion on the upstream side of the particulate filter 30 described above, an injector 8 for injecting and supplying a catalyst solution for promoting combustion of combustible particles in exhaust gas and an auxiliary combustion substance is provided. The injection port 8 a of the injector 8 has a filter 31
It is placed toward the surface of. An air pump 9 for supplying air is connected to the sprayer 8. Also,
The injector 8 is connected via a pump 10 to a tank 11 that stores a catalyst solution containing copper chloride (CuCl ₂ ) or the like for lowering the ignition temperature of combustible particles. Furthermore,
A switching valve 12 is inserted in a passage between the inlet port of the pump 10 and the tank 11, and a passage 13 branched from the switching valve 12 is used for assisting combustion of combustible particles. It is connected to a tank 14 that stores a solution containing an auxiliary combustion substance such as hydrogen. The tank 11 and the inlet port of the pump 10 communicate with each other at the ON position of the switching valve 12, and the tank 14 and the inlet port of the pump 10 communicate with each other at the OFF position. in this way,
The injector 8 is supplied with air by the pump 9 and the pump 1
0 supplies a catalyst solution or a solution containing a combustion-enhancing substance, and the supplied air causes these solutions to be injected through the injection port 8
It is ejected in a mist state from a toward the filter 31. 15
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 is not used and opens it when used. On the other hand, a flow path switching valve 17 is inserted in the air supply path 16 that communicates the air pump 9 and the injector 8 described above, and the branch path 18 branched from this switching valve 17 has an upstream side filter 31 and a downstream side. It communicates with the inside of the exhaust passage 6 a between the side filter 32. When the switching valve 17 is in the on position, the air pump 9 and the injector 8 are in communication, and in the off position, the air pump 9 and the exhaust passage 6a are in communication.

The exhaust passage portion 6b on the upstream side of the injection port 8a of the injector 8 and the exhaust passage portion on the downstream side of the particulate filter 30 are communicated with each other by the exhaust bypass passage 21, and the exhaust bypass passage 21 exhausts the exhaust gas from the engine 1 Can be passed around the injection port 8a of the injector 8 and the particulate filter 30. Also, the above passage 2
1, the exhaust passage 6 on the upstream end, that is, on the upstream side of the injection port 8a.
A flow rate control valve 22 that is a butterfly valve that controls the amount of exhaust gas that passes through the exhaust bypass passage 21 is provided at the connection portion with. The flow control valve 22 is connected to a diaphragm device 24 via a rod 23, and the diaphragm device 24
The negative pressure chamber 24a is communicated with a vacuum pump (not shown) via a negative pressure introducing passage 25. The negative pressure introduction passage 2
In the middle of 5, the negative pressure chamber 24 of the diaphragm device 24 is
A duty solenoid valve 26 that linearly switches the communication ratio between a and the vacuum pump or the atmosphere opening portion is arranged. The flow rate control valve 22 is driven and controlled by linearly operating the diaphragm device 24 by means of.

Reference numeral 41 denotes a control unit that controls the drive control of the above-mentioned respective units, and can be constituted by, for example, a microcomputer. Various signals indicating the operating state of the engine are input to the unit 41. For example, a signal indicating the exhaust temperature is input from the exhaust temperature sensor 42 arranged on the upstream side of the upstream filter 31, and the key switch 4
A key signal is input from 3. Further, a load signal is input from the accelerator opening sensor 44. Control·
The unit 41 outputs a control signal for drive control of each unit based on each input signal. In detail, in this example,
Oxygen deficiency in the exhaust passage is detected using a load signal, and when the load is high, it is determined that oxygen is deficient, and air is filtered from the air pump 9 serving as oxygen supply means by the filters 31, 32.
I am trying to supply it during.

FIG. 2 is a flow chart showing the operation of this embodiment centering on the air supply control.

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 Tex. Is read. Further, in step ST3, the load is read. Next, in the above clogging detection control, the filter 3
When 0 clogging is detected, the process proceeds from step ST4 to step ST5 along the flow of "YES" to drive the flow rate control valve 22 to open the bypass passage 21 at a predetermined opening degree, thereby exhausting the exhaust gas. The part is directly discharged to the atmosphere without passing through the clogged filter 30, thereby avoiding an abnormal rise in back pressure. After that, steps ST6 and ST7 are sequentially executed, the switching valve 12 is turned on so that the tank 11 and the injector 8 are communicated with each other, and the switching valve 17 is turned on and the air pump 9 is turned on.
And the injector 8 are in communication with each other.

Next, when the 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 ST8, ST9, ST1
After sequentially executing 0 to inject the catalyst solution, the process jumps from step ST11 to step 14 to close the opening / closing valve 15 and then close the bypass passage 21 in step ST15. However, if the exhaust temperature is 220 ° C or higher, 35
If the temperature is lower than 0 ° C, it is impossible to burn the combustible particles only by supplying the catalyst solution.
After performing ST, ST9, and ST10 sequentially to inject the catalyst solution, the process proceeds from step ST11 along the flow of “NO”. That is, steps ST12, ST13,
ST14 and ST15 are sequentially executed to inject a predetermined amount of the auxiliary combustion substance. When the exhaust gas temperature is lower than 220 ° C., the temperature is too low to burn the combustible particles, so that the exhaust gas temperature is waited to rise.

On the other hand, if clogging has not occurred, step ST
From step 4 to step ST16, it is determined whether the engine load is high. When the load is high, it is determined that the oxygen in the exhaust is not sufficient to burn the combustible particles, the process proceeds to step ST17, the switching valve 17 is turned off, and the air pump 9 and the filters 31, 32 are provided. It communicates with the exhaust passage portion 6a therebetween. Next, in step ST18, the air pump 9 is driven to supply air. As a result, in the downstream side filter 32, oxygen deficiency does not occur even when the load is high, and the combustible particles clogged in the filter 32 are completely combusted and CO or the like is not generated. However, if the load is not high,
The process proceeds from step ST16 along the flow of "NO", and thus air is not supplied. In this case, since the excess air ratio is high and the residual oxygen concentration in the exhaust gas is also high, incomplete combustion of combustible particles due to lack of oxygen does not occur in the downstream filter 32.

In the above example, the oxygen deficiency is detected based on the engine load, but it goes without saying that the oxygen concentration in the exhaust gas may be directly detected using, for example, an oxygen sensor. Also, oxygen deficiency may be detected based on the exhaust gas temperature.

(Effects of the Invention) As described above, according to the present invention, it is detected whether oxygen in exhaust gas is sufficient to burn the combustible particles in the filter, and if it is insufficient, Since oxygen is supplied between the upstream side filter and the downstream side filter, the combustible particles in the filter can always be completely burned, and therefore the regeneration from clogging of the filter can be effectively performed. Moreover, it is possible to avoid generation of CO and the like due to lack of oxygen. Furthermore, since oxygen is supplied between both filters, the sulfur components in the exhaust gas, such as when oxygen is supplied to the inlet portion of the upstream filter where the catalyst remains, are oxidized and harmful components such as SO ₃ are generated. This is preferable because it is not generated.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a flow chart showing the operation of the apparatus shown in FIG. 6 ... Exhaust passage, 8 ... Injector, 8a ... Injector, 9 ... Air pump, 10 ... Injector, 11 ... Tank, 12 ... Pump, 16 ... Air supply passage, 17 ... Switching valve, 18 ... Branch passage, 41 ... Control unit, 42 ... Exhaust temperature sensor, 44 ... Accelerator opening sensor.

Claims (1)

[Claims] 1. A filter means comprising a plurality of upstream and downstream filters for collecting combustible particles in exhaust gas arranged in series in an exhaust passage, and a catalyst component for lowering an ignition temperature of the combustible particles. A catalyst supply means for supplying the upstream side of the filter; a detection means for detecting whether or not oxygen in the exhaust passage is sufficient to burn the combustible particles trapped by the filter means; An exhaust gas purification device for a diesel engine, comprising: oxygen supply means for supplying oxygen between the upstream filter and the downstream filter when oxygen is insufficient based on the detection result of the means.