JPH052810B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas treatment device for a diesel engine, and more specifically, the present invention relates to an exhaust gas treatment device for a diesel engine, and more specifically, it removes carbon particles and similar particulate matter (hereinafter referred to as particulates or exhaust particulates) contained in exhaust gas by a physical method. The present invention relates to an exhaust particulate purification device (diesel particulate trap) suitable for collecting exhaust particulates on a suitable collecting material, periodically incinerating the collected exhaust particulates, and regenerating the collecting 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. Since then, heaters have generally been used. That is, 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 make the downstream particulates natural. However, this method consumes a large amount of power in the electric heater, and is not very preferable for automotive parts. Therefore, separately from this, the temperature of the exhaust gas is raised by throttling the intake system of the diesel engine without using a heater.
A method of burning exhaust particulates has also been proposed and implemented. However, with this method, the exhaust temperature rises sufficiently in the high load range of the engine, making it possible to incinerate the exhaust particulates, but in the low load range, the exhaust temperature does not rise sufficiently, making it difficult to incinerate the exhaust particulates and regenerate the collection material. The problem is that it is not possible. Furthermore, in order to raise the exhaust gas temperature, it is necessary to throttle the intake system excessively, but if the intake system is throttled too much, the oxygen (O ₂ ) concentration in the exhaust gas decreases, making it difficult to ignite. There is a flip side.

The purpose of the present invention is to eliminate the above-mentioned drawbacks,
To provide an exhaust particulate purification device for a diesel engine of an intake throttling type that does not use a heater, which is excellent in durability and safety, has a simple structure, and is low in cost.

In order to achieve such an object, according to the present invention, in addition to a normally open intake throttle valve provided in the intake system, a normally open exhaust throttle valve is provided in the exhaust system, so that the temperature of the exhaust gas can be adjusted. The rise is performed more by the exhaust throttle than by the intake throttle, and the intake throttle is kept to a necessary minimum to reduce excess air to some extent, mainly to reduce the burden on the exhaust throttle (of course, it also contributes to the rise in exhaust gas temperature).

The exhaust throttle valve is provided downstream of the collection material.
By closing both the intake throttle valve and the exhaust throttle valve during regeneration, the back pressure of the exhaust gas increases and the temperature of the exhaust gas increases to a temperature necessary for combustion of exhaust particulates. By providing an exhaust throttle valve downstream rather than upstream of the trap and restricting the exhaust gas on the downstream side, the temperature of the trap can be raised substantially simultaneously and uniformly throughout. Furthermore, in the present invention,
When the exhaust throttle valve is throttled, a so-called exhaust brake is applied, which reduces the engine output (torque).
However, the reduction in output is compensated for by operating the fuel injection increasing means to increase the amount of fuel injected to the engine when the exhaust throttle is throttled.
Therefore, the output and drivability of the diesel engine are not adversely affected. Furthermore, in the present invention, since the intake throttle is performed at the same time as the exhaust throttle, deterioration of fuel efficiency can be prevented. In other words, if you try to regenerate the particulate trap by raising the exhaust gas to the required temperature by only restricting the exhaust gas without restricting the intake air, generally in a diesel engine, intake air is always supplied in excess and the air-fuel ratio cannot be controlled by the amount of fuel. In order to control the amount of air, the amount of air is large and the burden on the exhaust throttle becomes considerable. As the amount of exhaust throttling increases, the output decrease increases accordingly, and therefore, the amount of fuel required to compensate for this output decrease increases, resulting in worsening fuel efficiency. Therefore, in the present invention, excess air is reduced to some extent by the intake throttle in advance, and the increase in fuel amount due to the exhaust throttle is minimized. Furthermore, if trap regeneration is performed only by exhaust throttling without intake throttling, e.g.
When performing trap regeneration during low-speed operation of about 30 miles/h, in order to raise the exhaust temperature to the temperature required for trap combustion regeneration, it is necessary to throttle the exhaust until the back pressure reaches 4 to 5 kg/cm ² abs. There is a possibility that things will blow up. In order to avoid such risks, it is advantageous to combine intake throttling and exhaust throttling as in the present invention.

Embodiments of the present invention will be described in detail below 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 trap container 10 is attached to a portion of the exhaust pipe on the downstream side of the exhaust manifold 4. Inside this trap container 10, there is a collection material (trap material) 12. The trap material does not impose excessive restrictions on the exhaust gas flow, allows the exhaust gas to flow through it, and is capable of trapping a significant amount of exhaust particulates contained in the exhaust gas. There is. The trap material must be made of a suitable material that can withstand the elevated temperatures reached during periodic combustion and ashing of the trapped exhaust particles during engine operation. is made into a suitable shape. Examples of materials suitable for such purposes include three-dimensional network foam ceramics, monolithic ceramics, bulk screen elements such as metal wire mesh or stainless steel.

In order to burn and ash the exhaust particulates collected by the trap material, it is usually necessary to raise the exhaust temperature to a level of approximately 560°C. Therefore,
The material of which the trap is constructed must be sufficiently resistant to 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 trap's location in the exhaust system, the temperature within the trap 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 certain traps are installed in the exhaust line downstream of the engine's exhaust manifold, as in FIG. Therefore, in order to periodically incinerate the collected particulates, it is necessary to provide some means to raise the exhaust temperature to the required level of approximately 560°C. The present invention employs an exhaust throttle as such exhaust temperature raising means. That is, an exhaust throttle valve 20 is provided in the exhaust system 15 downstream of the trap material, and the exhaust gas temperature is increased by throttling the exhaust gas. When the exhaust is throttled, the back pressure of the exhaust gas increases and the engine torque decreases. All of this reduced torque turns into heat, causing an increase in exhaust temperature. This exhaust throttle valve 2
0 is connected to a diaphragm valve 21 via a link, and this diaphragm valve 21 is connected to the vacuum pipe 1
3 and is connected to the negative pressure switching valve VSV22 and driven. While the VSV 22 is connected to the vacuum pump 8 via the vacuum pipe 23,
Microcomputer CPU 3 via wiring 24
Connected to 0. VSV22 normally has its atmospheric port open, and the diaphragm valve 21
The atmosphere acts on the exhaust throttle valve 20 to open it. Wiring 2 from microcomputer CPU30
4, the atmospheric port of the VSV 22 is closed, and the negative pressure from the vacuum pump 8 acts on the diaphragm valve 21 through the vacuum piping 23 and the VSV 22, which closes the throttle valve 20 and exhausts the air. The tube 15 is approximately 90 mm deep in its passageway.
Narrow it down by about %.

As mentioned above, when exhaust throttle is performed, a decrease in output (torque decrease) occurs, so the amount of fuel is increased to compensate for this. Therefore, in the present invention, means for increasing the amount of fuel injection supplied to the engine is provided. That is, an actuator 31 that controls the plunger position of the fuel injection pump 5 is provided. This actuator 31 is, for example, an injection nozzle 7 of a fuel injection pump 5.
The diaphragm valve 31 may be connected via a link mechanism 65 to a spill ring 61 that controls the fuel injection time (FIG. 2). Diaphragm valve 31
is connected to the VSV 18 via vacuum piping 16 and is driven thereby. The VSV 18 is connected to the CPU 30 via wiring 32 and to the vacuum pump 8 via vacuum piping 19. Therefore, microcomputer CPU3
When a signal is transmitted from 0 through wiring 32,
The actuator 31 moves the plunger 66 of the fuel injection pump 5 using the spill ring 61 to increase the fuel injection amount.

Such a fuel injection valve itself and a fuel increase mechanism itself are well known and will not be described in further detail.

Further, as described above, if an attempt is made to raise the exhaust temperature only by exhaust throttling, various problems such as deterioration of fuel efficiency will occur, so in the present invention, intake throttling is also performed. For this purpose, an intake throttle valve 40 is provided at the inlet of the intake manifold 3. Intake throttle valve 4
0 is connected to a negative pressure operated diaphragm valve 43 via a link 41, and this diaphragm valve 43 is connected to a vacuum pump 8 via a negative pressure switching valve VSV45 and a vacuum pipe 46. Further, the negative pressure switching valve 45 is connected to the microcomputer CPU 30 via a wiring 44. Therefore,
When a command signal is input from the CPU 30 to the negative pressure switching valve 45 through the wiring 44, the negative pressure switching valve 45
The vacuum path is opened, and negative pressure from the vacuum pump 8 passes through the pipe 46 to the diaphragm valve 43.
is transmitted to the intake throttle valve 40 via a link 41.
operate in the closing direction. This is a throttling means that throttles the intake passage. The opening degree of the throttle valve 40 is detected by a throttle sensor 48 via a wiring 42 and input to the CPU 30 via a wiring 49.

The intake throttle valve 40 and the exhaust throttle valve 20 described above
and the fuel injection amount increasing means are periodically operated in conjunction with each other during operation of the diesel engine,
Combustion and ashing of the exhaust particulates and regeneration of the trap container 10 are carried out, and the start timing of such regeneration operation and the operation of the means described above are controlled by the microcomputer CPU 30. For this purpose,
Engine operating conditions, exhaust gas conditions, etc. are detected and input to the CPU 30. That is, in FIG. 1, 50 is the engine load, 51 is the engine speed, 52 is the engine water temperature, 54 is the exhaust gas temperature before the trap, 55 is the temperature inside the trap, 56 is the exhaust gas temperature at the trap outlet, Each of these detection signals is input to the CPU 30.

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

1. The trap must be cleaned often enough so that 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 trap bed is not damaged.

To achieve these objectives, in the present invention, the microcomputer CPU 30 is programmed to operate as shown in FIG.

In FIG. 3, first, it is determined whether or not it is regeneration time based on signals such as engine speed 51, engine load 50, trap floor temperature 55, trap outlet exhaust temperature 56, and engine water temperature 52. The next regeneration is programmed so that the next regeneration will be determined after the previous regeneration has been completed and the vehicle has traveled approximately 90km. This is because the trap becomes overloaded after traveling about 400 km, so a cleaning interval of about every 70 km is considered appropriate. After it is determined that it is time for regeneration, control is performed by means as shown in the flowchart of FIG. 3, and the intake throttle valve 40 and exhaust throttle valve 20 are closed for an appropriate time and the amount of fuel injection is increased. Ru. This raises the exhaust temperature to a temperature necessary to incinerate exhaust particulates.
In the embodiment shown in FIG. 3, 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. Also, troubles during trap regeneration (for example, abnormal rise in exhaust gas temperature, etc.) are also dealt with.

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 intake and exhaust system and increasing the amount of fuel, the exhaust temperature is lower than that required for combustion and ashing of exhaust particulates.
A temperature of 560℃ can be obtained. It is also believed that throttling the exhaust system does not have a large effect on boost pressure.

Incidentally, since the exhaust throttle has the effect of reducing HC and NOx, the present invention is also advantageous in terms of measures against exhaust gas emissions.

Furthermore, it is also possible to lower the combustion start temperature of particulate by supporting a catalyst within the particulate trap.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a diesel engine using the device of the present invention, FIG. 2 is an illustrative diagram showing a fuel increase mechanism, and FIG. 3 is a flowchart showing a control process according to the present invention. DESCRIPTION OF SYMBOLS 1... Diesel engine main body, 5... Fuel injection pump, 10... Trap container, 20... Exhaust throttle valve, 21... Exhaust throttle valve actuator, 3
0...Microcomputer CPU, 31...Fuel injection pump increase actuator, 40...Intake throttle valve, 43...Intake throttle valve actuator.

Claims (1)

[Claims] 1. In a diesel engine with a fuel injection valve that has a collection material for exhaust particulates in the exhaust gas path, a normally open intake throttle valve and a normally open exhaust throttle valve are installed downstream of the collection material in the intake system and exhaust system of the engine, respectively. A diesel engine characterized in that it is provided with a fuel injection increasing means for increasing the injection amount of a fuel injection valve, and is provided with a means for closing an intake throttle valve and an exhaust throttle valve and operating the fuel injection increasing means at the time of regeneration. Engine exhaust particulate purification device.