JPH0253604B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas treatment device for a diesel engine, and more particularly to a device for removing carbon particles and similar particulate matter (hereinafter referred to as exhaust particles) contained in exhaust gas by a physical method. The present invention relates to an exhaust particulate purification device suitable for collecting on an appropriate collection material, periodically incinerating the collected exhaust particulates, and regenerating the collection material.

Most of these types of exhaust particulates are flammable, such as carbon particles, and conventional methods have been used to collect these flammable particulates, incinerate the collected particulates, and regenerate the collection material. The following methods are known.

(1) 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.

(2) A method in which an oil burner is installed in the exhaust system of a diesel engine to raise the temperature of exhaust gas to a temperature at which exhaust particulates are combusted.

(3) A method in which an electric heater is attached to the entire surface of the collection material to burn the exhaust particulates adhering to the surface of the collection material, and use this as a heat source to cause the downstream particulates to self-combust.

Recently, the same applicant as this application has proposed a device that combines the methods (1) and (3) above to burn exhaust particulates and regenerate the collection material (particularly (Gan Sho 56-96614). However, even if the exhaust temperature is raised by restricting the intake system and the ignitability of exhaust particulates is improved by the electric heater, the engine operating conditions (for example, when the engine usage changes during regeneration) Therefore, the exhaust particulates (particulates) may still not be ignited even by the electric heater.

The purpose of the present invention is to eliminate the above-mentioned drawbacks,
To provide an exhaust particulate purification device for a diesel engine that is excellent in durability and safety, has a simple structure, is low in cost, and has good ignition properties for exhaust particulates.

In order to achieve such an object, the present invention provides an exhaust particulate purification device for a diesel engine having an exhaust particulate collecting material in the exhaust pipe, in which a throttle valve is provided in the exhaust pipe downstream of the collecting material. It is characterized in that it further includes an electric heater disposed on the upstream end surface of the collection material, and means for increasing the amount of fuel injection supplied to the engine. The fuel increase means, exhaust throttle valve and electric heater are operated in conjunction periodically during engine operation.

Since such a throttle valve is installed downstream of the collection material, by throttling the throttle valve, the back pressure at the location of the collection material increases directly and quickly, and the temperature of the exhaust gas decreases to the level of the exhaust particulate matter. The temperature rises to the temperature required for combustion. Furthermore, the exhaust flow velocity inside the collection material or on its upstream surface becomes smaller, making it easier for the electric heater to ignite the exhaust particles. That is, cooling loss can be reduced. Furthermore, since the amount of fuel injected to the engine is increased when the exhaust throttle valve is throttled, the output and drivability of the diesel engine are not adversely affected. The fuel injection amount increasing means and the exhaust throttle valve are controlled by a computer or the like so as to operate periodically in conjunction with each other during engine operation.

Preferably, the electric heater is a plurality of (ceramic) electric heater elements arranged in a distributed manner.
It is preferable to reduce power consumption as much as possible by energizing and heating each heater element in turn.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In Fig. 1, 1 is the diesel engine body, 2 is the transmission, 3 is the intake manifold, 4 is the exhaust manifold, 5 is the fuel injection pump,
6 is a fuel pipe, 7 is a fuel injection valve (injector),
8 is a vacuum pump, 9 is a cooling fan, and these are the components of a normal diesel engine.

A trapping material container 10 is attached to a portion of the exhaust pipe on the downstream side of the exhaust manifold 4. Inside the trapper container 10, as shown in FIG. 2, there is a trapping material 11.
This trap material 11 is designed to allow the exhaust gas to flow through it without causing excessive restriction on the flow of the exhaust gas, and to trap a considerable amount of exhaust particulates contained in the exhaust gas. It's summery. In addition, the trap material 11 is made of an appropriate material that can sufficiently withstand the elevated temperature that is to be reached during combustion and ashing of exhaust particulates collected thereon periodically during engine operation. It is made of suitable materials and in a suitable shape. Examples of materials suitable for this purpose include foamed ceramics with three-dimensional network structures, monolithic ceramics, and metal wires.
There are bulk screen elements such as mesh or stainless steel.

In order to burn and ash the exhaust particulates collected by the trap material 11, it is usually necessary to raise the exhaust temperature to a level of approximately 560°C. Therefore, the material of which the trap is made must be able to withstand this temperature.

However, experience has shown that during normal engine operation (in the absence of special measures to increase the exhaust temperature) the temperature in the exhaust system varies considerably under different conditions of engine load and speed. Also, depending on the particulate trapper's location in the exhaust system, the temperature within the trapper may never reach the level necessary to burn off the particulates collected therein. This may be the case if the engine is not operated under full throttle, as is typical in many automotive applications, if it is equipped with a turbocharger, or if the arrangement shown in Figure 1 is used. This is particularly the case when the particular trapper is mounted in the exhaust line downstream of the engine's exhaust manifold, as in the example in FIG. Therefore, in order to periodically incinerate the collected particulates, it is necessary to provide some other means to raise the exhaust temperature to the required level of approximately 560°C.

A number of possible methods can be used singly or in combination to obtain the desired temperature level. One such method, which can be used under all engine operating conditions except full fuel or full load conditions, is to throttle the engine's exhaust system. It has been found that appropriate throttling of the exhaust gas can substantially increase the exhaust temperature of the engine, and in some cases may be sufficient to raise the temperature within the particle trapper to ashing levels.

That is, in the present invention, the exhaust throttle valve 20 is provided at an appropriate position downstream of the trapper container 10 in the exhaust pipe line, which is not normally throttled. The exhaust throttle valve 20 is connected via a link to a diaphragm valve 21, which is driven by a voltage switching valve (VSV) 22. The VSV 22 is connected to a vacuum pump 8 via a vacuum pipe 23 and to a microcomputer (CPU) 30 via a wiring 24. The VSV 22 normally has its atmospheric port open, and the atmosphere acts on the diaphragm valve 21 to open the exhaust throttle valve 20. Microcomputer (CPU) 3
When a signal is transmitted from 0 through the wiring 24,
The atmospheric port of the VSV 22 is closed, and the negative pressure from the vacuum pump 8 is applied to the vacuum pipe 23,
acts on the diaphragm valve 21 through the VSV 22,
This closes the throttle valve 20 and throttles the exhaust pipe by about 90% of its passage. In addition, the exhaust throttle valve 20
may be provided on the downstream side of the trapper container 10.

Further, in the present invention, means is provided for increasing the amount of fuel injection supplied to the engine. That is, a negative pressure switching valve (VSV) 31 is provided to control the fuel increase device 33 of the fuel injection pump 5.
The VSV 31 is connected to a microcomputer (CPU) 30 via wiring 32 and to a vacuum pump 8 via piping 34. Therefore, microcomputer (CPU) 3
When a signal is transmitted from 0 through wiring 32,
The VSV 31 is connected to the fuel increaser 33 through the pipe 34.
This fuel increasing device 33 operates to increase the fuel injection amount.

Furthermore, in the present invention, an electric heater device 12 is provided at the upstream end of the trapper 11 as an auxiliary means for igniting and burning exhaust particulates.
The electric heater device 12 includes a plurality of electric heater elements or ceramic heater elements 1 disposed in a distributed manner.
Consists of 3. Each heater element 13 is not made of a coil-like winding like a normal electric heater, but is formed in a planar zigzag shape as shown in FIG. To attach such a heater element 13, a honeycomb-shaped ceramic filter 14 is used.
A plurality of heater elements 13 are attached in a distributed manner to the ceramic filter 14 and the trap material 1.
It can be fixed by interposing it between 1 and 1. Note that 15 is a terminal for supplying current to each heater element, and 18 is a ground wire. The size, number, and arrangement of each heater element 13 (FIG. 3) are selected so as not to impede the flow of exhaust gas and thus to minimize the increase in exhaust gas back pressure; Power is applied one by one. The current supply terminal 15 is connected to a microcomputer (CPU) 30 via a voltage converter 16 (FIG. 1) and wiring 17.

The exhaust throttle valve 20, the fuel injection amount increasing means, and the electric heater device 12 described above are periodically operated in conjunction with each other during operation of the diesel engine to burn, ash, and trap exhaust particulates.
0 is played back, and the start timing of such playback operation and the operation of the means are controlled by a microcomputer (CPU) 30.
For this purpose, engine operating conditions, exhaust gas conditions, etc. are detected and input to the CPU 30. That is, the first
In the figure, 50 is the engine load, 51 is the engine speed, 52 is the engine water temperature, 53 is the exhaust pressure before the trapper, 54 is the exhaust gas temperature before the trapper,
55 is the temperature inside the trapper, 56 is the exhaust gas temperature at the outlet of the trapper, and each of these detection signals is
It is input to the CPU 30. Note that 57 is a back pressure sensor that detects the exhaust pressure before the trapper.

The following points should be kept in mind in such a control system.

1. The trapper must be cleaned often enough so that the collected particulates do not create undue restrictions on the exhaust gas flow.

2 Throttling and fuel addition of the engine exhaust system must be controlled so as not to significantly alter the drivability or performance of the vehicle.

3. The control process should not result in a significant or noticeable increase in smoke emanating from the vehicle exhaust pipe.

4. The combustion cycle should be controlled so that only particulates are burned and ashed and the trapper bed is not damaged.

In order to achieve these objectives, in the present invention, a microcomputer (CPU 30) is programmed to operate as shown in FIG.

In FIG. 5, first, engine speed 51, engine load 50, trapper bed temperature 55, back pressure 53,
It is determined whether it is time for regeneration based on signals such as the trapper outlet exhaust gas temperature 56 and the engine water temperature 56. The determination of the regeneration timing is programmed so that the next regeneration will be performed after the vehicle has traveled approximately 70km after the previous regeneration was completed. This is because the Toratsupa becomes overloaded when traveling about 400 km.
A cleaning interval of approximately every 70km is considered appropriate. After determining that it is time for regeneration, control is performed by means as shown in the flowchart of FIG. That is, the exhaust throttle valve is throttled, the amount of fuel injection is increased, and the exhaust temperature is raised to a temperature necessary for incinerating exhaust particulates. When the exhaust temperature exceeds 560℃,
The electric heater 12 on the front side of the trapper is energized for 20 seconds. Incidentally, troubles during trapper regeneration (for example, abnormal rise in exhaust gas temperature, etc.) are handled as shown in the flowchart. When the trapper (internal) bed temperature is below 660℃ (however, the exhaust gas temperature at the trapper inlet is above 560℃) and the exhaust temperature after the trapper remains below 580℃ for 2 minutes, regeneration is completed and the microcomputer (CPU) is reset. Ru. In the embodiment shown in FIG. 5, the combustion time is set to 2 minutes, but it can be set to an appropriate time depending on the accumulation of exhaust particulates and other conditions.

FIG. 4 shows the state of combustion of exhaust particulates by the heater element 13. The heater element 13 is arranged on the upstream end face of the trap material 11, so when it is heated by electricity, it burns the exhaust particulates adhering to the vicinity and burns them along the flow of exhaust gas shown by the arrow P. The combustion flame is propagated downstream. In FIG. 4, region A is the part where exhaust particulates are burned and trap material is regenerated,
Although region B is a part that is not recycled, in reality, since a plurality of electric heater elements 1 are attached, the entire area of trapping material 11 can be recycled. Therefore, the number of electric heater elements 13 and their arrangement may be determined to the minimum necessary number so that the exhaust particulates can be completely burned over the entire area of the trapper material 11.

As mentioned above, if the plurality of heater elements 13 are energized in order, power consumption can be reduced, and the collection material 11
It is possible to effectively ignite and burn the accumulated exhaust particulates. Note that the present invention can also be applied to a diesel engine equipped with a turbocharging mechanism. This type of engine has a lower exhaust temperature than a normal engine, but by restricting the exhaust system and increasing the amount of fuel, the combustion of exhaust particulates is reduced.
The temperature of 560°C required for ashing can be obtained, and the spark plug easily ignites exhaust particulates.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a diesel engine using the present invention, Fig. 2 is a partial cross-sectional view of the trapper container, Fig. 3 is a detailed view of the front end of the trapper material, and Fig. 4 is a diagram showing the removal of exhaust particulates by the heater element. A diagram showing the combustion situation,
FIG. 5 is a flowchart of a reproduction control process by a microcomputer (CPU). DESCRIPTION OF SYMBOLS 1... Diesel engine main body, 5... Fuel injection pump, 10... Trapper container, 11... Collection material (trapper material), 12... Electric heater device, 1
3... Heater element, 20... Exhaust throttle valve, 30...
...Microcomputer (CPU), 31...actuator.

Claims (1)

[Claims] 1. In a diesel engine having a collection material for exhaust particulates in an exhaust gas path, an exhaust throttle valve is provided in the exhaust gas path downstream of the collection material, and an electric heater is arranged on an upstream end surface of the collection material. Further, means for increasing the amount of fuel injection supplied to the engine is provided, and control means is provided for periodically operating the fuel injection amount increasing means, the throttle valve, and the electric heater in conjunction with each other during engine operation. . An exhaust particulate purification device for a diesel engine, which periodically burns exhaust particulates accumulated in the collection material to regenerate the collection material.