JPH0425414B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an exhaust purification device for a diesel engine, and more specifically, carbon particles and similar particulate matter (hereinafter referred to as exhaust particulates) contained in exhaust gas are removed from a filter element by a physical method. A trap regeneration device in a diesel engine exhaust purification device suitable for collecting the collected exhaust particulates in a trap containing an appropriate collection material (filter), periodically incinerating the collected exhaust particulates, and regenerating the filter. Regarding. Prior Art Most of the exhaust particulates contained in the exhaust gas of diesel engines are flammable, such as carbon particles, and these combustible particulates are collected and collected by incineration. The following methods have been known for recycling materials, and each method has the following drawbacks. A method of throttling the intake system of a diesel engine to reduce the amount of intake air and raise the temperature of exhaust gas to burn exhaust particulates. With this method, the exhaust temperature rises sufficiently in the high speed range of the engine, making it possible to incinerate the exhaust particulates, but in the low and medium speed ranges, the exhaust temperature does not rise sufficiently, making it difficult to incinerate the exhaust particulates and regenerate the collection material. becomes impossible. A method of attaching an electric heater to the entire surface of the filter, burning the exhaust particulates attached to the filter surface, and using this as a heat source to cause the downstream particulates to self-combust. In this method, since an electric heater is attached to the entire surface of the filter, power consumption is very large, and in order to reduce power consumption, various measures are required and the cost is also high. On the other hand, in order to solve the above-mentioned problems, the present applicant first collected exhaust particulates,
In a multi-cylinder diesel engine in which a combustion particulate collection trap is disposed in the exhaust pipe, the fuel passages of at least one set of cylinders in which the explosion stroke and exhaust stroke overlap are connected via a communication passage, and the particulate collection trap is During combustion regeneration of the collection trap, a portion of the fuel destined for the explosion cylinder is sent directly to the exhaust stack, that is, the inside of the cylinder 2
We have proposed a trap regeneration device for a diesel engine exhaust purification system that performs a secondary injection and thereby causes high-temperature exhaust gas to flow into a particulate collection trap. However, even in such a system that performs in-cylinder secondary injection, the regeneration of the filter in the trap in the low to medium speed range is still not sufficient in the engine high speed range, and a countermeasure for this problem has been desired. Purpose of the Invention The present invention has been devised in view of the problems of the prior art as described above as well as the unresolved problems of the in-cylinder secondary injection method proposed by the applicant, and its purpose is to is able to burn exhaust particulates in the filter by raising the temperature of the exhaust gas without requiring electricity, and is capable of sufficiently burning exhaust particulates not only in the high-speed range of the engine but also in the low-to-medium speed range. An object of the present invention is to provide a trap regeneration device in an exhaust purification device for a diesel engine that can perform the following functions. Composition of the Invention In order to achieve the above object, the present invention includes sensors that detect each of load, rotation speed, and exhaust temperature, a computer to which detection signals from these sensors are input, and opening and closing of the sensors controlled by this computer. A secondary fuel injection mechanism whose operation is controlled by the same computer and injects fuel into the cylinder during its exhaust stroke, and an unburned gas reaction catalyst installed in a trap in the exhaust path. The trap regeneration device in the exhaust purification system of a diesel engine is equipped with a trap regeneration device that performs intake throttling in the high-speed range of the engine, and performs secondary fuel injection or both secondary fuel injection and intake throttling in the same low and medium speed range. It is a structural feature. Embodiments Examples of the present invention will be described below with reference to the drawings. In Figure 1, 1 is the diesel engine body;
2 is a fuel injection pump, and in addition to supplying fuel to each cylinder as usual, this fuel injection pump 2 also injects secondary fuel during the exhaust stroke of a specific cylinder. This will be discussed later. Reference numeral 3 denotes an intake throttle valve provided in the intake passage, which is opened and closed by a diaphragm 4 for driving the intake throttle valve, and this diaphragm 4 is operated by negative pressure from a vacuum pump 5. It's summery. 6 and 7 are vacuum switching valves (abbreviated as negative pressure switching valves, VSV) provided in the negative pressure passage 8 that connects the vacuum pump 5 and the diaphragm 4 for driving the intake throttle valve; The operation of the intake throttle valve driving diaphragm 4 is controlled depending on whether negative pressure or atmospheric air is introduced into the switching valve. The negative pressure switching valves 6 and 7 are both connected to a computer 9, and based on commands from the computer 9, switching between the introduction of negative pressure and atmospheric air is controlled as described above. The reason why two negative pressure switching valves are provided is to not only simply control the opening and closing of the intake throttle valve 3 on and off, but also to freely adjust the degree of opening and closing by controlling the duty ratio of the opening and closing. . 10
is a trap installed in the exhaust passage, which houses a filter made of foamed ceramic or similar materials, and a catalyst is attached to the surface of this filter to react and burn unburned gas (CO, HC, etc.). There is. The filter in this trap has a three-dimensional mesh structure, through which exhaust gas can flow, and exhaust particulates such as carbon contained in the exhaust gas can be collected between the meshes. I'm starting to be able to do it. Reference numeral 11 denotes an exhaust gas temperature sensor provided in the exhaust passage, and a detection signal of the exhaust gas temperature is input to the computer 9. Reference numeral 12 denotes a bypass valve provided in the exhaust passage, and is operated by a diaphragm 13 for driving the bypass valve. This bypass valve driving diaphragm 13 is connected to the vacuum pump 5 via a negative pressure switching valve 14, and the negative pressure switching valve 14 is connected to a computer 9 and controlled by instructions thereof. Reference numeral 15 denotes an exhaust gas pressure sensor provided downstream of the trap 10, which is connected to the computer 9, detects the exhaust gas pressure, inputs the signal to the computer 9, and determines whether the trap 10 needs to be regenerated. It is something that can be done. Note that trap regeneration may be determined by integrating the number of revolutions of the engine, and the computer 9 may issue a command when a certain cumulative number of revolutions is reached. 16 is an engine cooling water temperature sensor;
17 is a load sensor, 18 is a rotation sensor, 19 is a throttle opening sensor, and 20 is a suction pressure sensor, and the detection signals of these sensors are sent to the computer 9.
It is now entered into . 21 is an exhaust gas recirculation valve. FIG. 2 shows the piping configuration of the secondary fuel injection for sending high-temperature exhaust gas to the trap 10 in this embodiment. Fuel injection nozzle 22
Fuel is supplied to A, 22B, 22C, and 22D via fuel passages 23, 25, 27, and 29 as usual. By the way, in the case of a multi-cylinder engine, the explosion stroke and exhaust stroke of a certain set of cylinders always occur overlappingly.
In other words, taking a four-cycle case of a four-cylinder engine as an example, the results are as shown in Table 1 below.

[Table] In the table above, the meaning of each letter is as follows. Pressure...Compression, Explosion...Explosion, Exhaust...Exhaust, Intake...Intake As is clear from Table 1, when the first cylinder (#1) is in the explosion stroke, the second cylinder (#2) is in the exhaust stroke, and so on. 2nd cylinder explosion and 4th cylinder exhaust, 3rd cylinder (#3) explosion and 1st cylinder exhaust,
The explosion of the fourth cylinder (#4) and the exhaust of the third cylinder overlap. Therefore, in this embodiment, the fuel passages of one or more sets of cylinders in which explosion and exhaust overlap are connected to each other via a communication passage.
The fuel passage 23 for the #1 cylinder and the fuel passage 25 for the #2 cylinder are connected to the communication passage 24, and the fuel passage 27 for the #3 cylinder and the fuel passage 29 for the #4 cylinder are connected to the communication passage 24, respectively.
28. And these communication paths 2
Check valves 33 and 37 that allow fuel to flow only in the direction from the explosion cylinders (#1 and #4) to the exhaust cylinders (#2 and #3), respectively, are disposed in the insides of the cylinders 4 and 28.
is provided. The check valves 33, 37 may be known per se, for example spring-loaded ball check valves.
Furthermore, switching valves 31 and 35 are provided in these communication passages 24 and 28. The switching valves 31 and 35 may be, for example, solenoid plunger electromagnetic valves which are known per se, and control the opening and closing of the communication passages 24 and 28 based on a control signal from the computer 9.
That is, the switching valves 31 and 35 are always in the closed position,
The valve is opened by the computer 9 only during trap regeneration. These switching valves 31 and 35 make the fuel passages of each cylinder independent from each other except during trap regeneration.
It is provided to supply the engine with its own fuel. The operation of this embodiment having the above configuration is as follows. During engine operation, the computer 9 determines whether or not regeneration of the trap 10 is necessary based on the detection result of an exhaust gas pressure sensor 15 installed downstream of the trap 10. Then, when it is necessary to regenerate the trap 10, the operation is started. When the computer 9 determines that the engine is in the high speed range based on the detection signals of the load sensor 17 and rotation sensor 18, the command is transmitted to the negative pressure switching valves 6 and 7, and these negative pressure switching valves switch their atmospheric ports to When closed, the negative pressure from the vacuum pump 5 acts on the intake throttle valve driving diaphragm 4 via the negative pressure passage 8 and the negative pressure switching valves 6 and 7, thereby controlling the intake throttle valve 3 to the target pressure of the suction pressure sensor 20. Close until. Generally, when the intake air is throttled, excess air decreases and the temperature of the exhaust gas increases. Set it to pressure. (The fuel temperature of exhaust particulates such as carbon is approximately 600℃,
If a catalyst is installed, the combustion temperature will be lowered even further. ) As a result, the temperature of the exhaust gas flowing into the trap 10 rises to the temperature of the exhaust particulate fuel, the particulates collected by the filter are combusted, and the function of the trap can be restored. At this time, the throttle opening sensor 19 detects the throttle opening, and if the opening exceeds the set value (if the load becomes large), the computer 9 commands:
Negative pressure is introduced into the bypass valve driving diaphragm 13 via the negative pressure switching valve 14, and the bypass valve 12 is opened to reduce the pressure loss that the trap 10 gives to the engine 1. In this manner, in the high speed range, by throttling the intake air, the temperature of the exhaust gas is raised, and the exhaust particles in the trap can be combusted. On the other hand, when it is determined that the engine is in the low-medium speed range based on the detection of the load sensor 17 and the rotation speed sensor 18, the switching valve 31 and the switching valve 35 are opened by a command from the computer 9.
Fuel passage 2 to be injected just before the cylinder's explosion stroke
A part of the fuel in No. 3 is passed through the communication path 24 to the check valve 33.
The fuel flows into the fuel passage 25 while opening the valve, and is also secondarily injected into the #2 cylinder from the fuel injection nozzle of the #2 cylinder. At this time, the #2 cylinder has completed its explosion stroke and is in the beginning of its exhaust stroke, but the fuel injected into the #2 cylinder comes into contact with the high-temperature combustion gas from the explosion stroke that remains in the cylinder, generating CO and HC. This is discharged into the exhaust path. In exactly the same way, when the #4 cylinder explodes, part of the fuel for the #4 cylinder is supplied to the #3 cylinder during the exhaust stroke, generating CO and HC, which are discharged into the exhaust path. And trap this CO, HC10
The internal temperature of the trap 10 is increased by the generated heat, and the exhaust particulates collected by the filter are incinerated.
In this case, if the exhaust temperature sensor 11 detects that the temperature rise in the trap 10 is insufficient, the computer 9 issues a command to the negative pressure switching valves 6 and 7.
The intake throttle valve 3 is controlled to close by introducing negative pressure into the intake throttle valve driving diaphragm 4 through these negative pressure switching valves, thereby acting to further increase the exhaust gas temperature. In this way, in the low and medium speed range of the engine, the temperature inside the trap 10 is increased by the unburned gas reaction heat generated by the secondary injection of fuel, and if the temperature rise is still insufficient, the intake air is throttled further. As a result, the exhaust gas temperature can be increased to incinerate the exhaust particulates in the trap. Although the above secondary injection of fuel is performed between two sets of cylinders, it is not necessarily performed between two sets of cylinders, and may be performed only between one set of cylinders.
In addition to the above combinations, there are also combinations of explosion cylinders and exhaust cylinders: #2 cylinder and #4 cylinder, #3 cylinder and #1 cylinder.
Possible examples include cylinders, etc. Effects of the Invention As explained above, the present invention uses a combination of the intake throttle, secondary fuel injection into the cylinder, and the catalyst in the trap to achieve low engine speed in the engine high-speed range with only the intake throttle. In the medium speed range, the exhaust gas temperature can be raised to a temperature at which exhaust particulates can be combusted by secondary fuel injection in the cylinder, or by further restricting the intake air if this is insufficient. A trap regeneration device for a diesel engine exhaust purification device that is durable, safe, has a relatively simple structure, and is low cost can be obtained, as the trap is sufficiently regenerated in all operating ranges and power consumption can be reduced. belongs to.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing the entire embodiment of the present invention;
FIG. 2 is a fuel piping diagram for secondary fuel injection in the same embodiment. 1... Diesel engine body, 2... Fuel injection pump, 3... Intake throttle valve, 9... Computer, 10... Trap, 11... Exhaust temperature sensor,
17...Load sensor, 18...Rotation sensor, 20
...Suction pressure sensor, 23, 25, 27, 29...
...Fuel passage, 24, 28...Communication passage, 31, 35
...Switching valve, 33, 37...Check valve.

Claims (1)

[Scope of Claims] 1. Each sensor that detects each of load, rotation speed, and exhaust temperature, a computer to which the detection signals of these sensors are input, and an intake throttle valve whose opening and closing are controlled by this computer. It is equipped with a secondary fuel injection mechanism that is controlled by the same computer and injects fuel into the cylinder during the exhaust stroke of the cylinder, and an unburned gas reaction catalyst installed in a trap in the exhaust path. Now, the intake throttle,
A trap regeneration device in an exhaust purification device for a diesel engine that performs secondary fuel injection or both secondary fuel injection and intake throttling in the medium and low speed range. 2. The configuration of the secondary fuel injection mechanism is such that fuel can only flow from the explosion cylinder side toward the exhaust cylinder side between the fuel passages of at least one set of cylinders where the explosion stroke and exhaust stroke overlap. 2. A trap regeneration device in an exhaust purification system for a diesel engine according to claim 1, which is connected through a communication path having a stop valve and is provided with a valve in the communication path that opens only during trap regeneration.