Exhaust gas cleaning device for internal combustion engine

Details Exhaust gas cleaning device for internal combustion engine Exhaust gas cleaning device for internal combustion engine

2003-06-13

2004-12-14

Tran, Binh Q. (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

By means producing a chemical reaction of a component of the...

C060S284000, C060S287000, C060S295000, C060S297000

Reexamination Certificate

active

06829889

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas cleaning device for an internal combustion engine, and more particularly, the invention relates to the technology of recycling a particulate filter.
2. Description of the Related Art
Generally, there is increasing demand for the continual reduction of exhaust emissions from internal combustion engines used in automobiles and the like, and particularly in compression ignition type diesel engines that use diesel oil as fuel. CO, HC, and NOx are not the only gases desired to be removed from the exhaust gas, but also smoke and fine exhaust particles such as SOF contained in the exhaust gas. Therefore, a particulate filter is provided in the exhaust path to capture the fine particles contained in the exhaust gas.
The particulate filter lets an incoming exhaust gas pass through its porous diaphragm to capture fine particles present in the exhaust gas on the surface or fine pores of the diaphragm. As the quantity of particles to be captured and deposited increases to an excessive quantity, the back pressure in the internal combustion engine is raised as the flow resistance caused by the particulate filter increases. This decreases the performance of the engine. Therefore, fine exhaust particles captured by the particulate filter must be appropriately removed from the filter, so that the particulate filter can be recycled to restore its capability of capturing fine particles from the exhaust.
A known particulate filter includes an oxidation catalyst, such as platinum, provided in the filter enabling it to be recycled by the oxidation function of the catalyst during operation of the internal combustion engine. In this particulate filter, for example, post injection of fuel in the exhaust process supplies fuel to the particulate filter, so that the heat from the catalytically oxidized fuel is used to oxidize and remove deposited fine exhaust particles that are not oxidized as easily as the injected fuel.
Frequent recycling of the particulate filter degrades fuel efficiency while, if the recycling interval is too long, part of the excess of the deposited fine exhaust particles could abruptly burn, resulting in the particulate filter attaining abnormally high temperatures and becoming damaged. Therefore, the quantity of the deposited fine exhaust particles is preferably measured to determine when to start recycling. According to the disclosure of Japanese Patent Laid-Open Publication No. Hei 7-332065, the differential between the pressure at the inlet and at the outlet of the particulate filter is measured to allow a determination based on the fact that the differential pressure increases because of an increase in the flow resistance caused by the increased quantity of fine exhaust particles in the filter. Then, the point in time when the detected differential pressure is beyond a prescribed value is determined as the recycling time.
According to Japanese Patent Laid-Open Publication No. Hei 7-332065, however, the quantity of deposited fine exhaust particles could be different for the same detected differential pressure, depending on the operation state of the internal combustion engine. Accordingly, the quantity of deposited fine exhaust particles cannot necessarily be determined with sufficient accuracy. Detailed maps for different operation states could be stored, but cannot be easily provided for, as a large storage capacity would be necessary.
SUMMARY OF THE INVENTION
The invention is directed to a solution to the above-described disadvantage, and it is an object of the present invention to provide an exhaust gas cleaning device for an internal combustion engine in a simple structure that can properly determine the time of recycling the filter.
The inventors have researched and studied the particulate filter in connection with the deposition of fine exhaust particles and its effect upon the flow of the exhaust gas, and have found that the following model equation is established.
&Dgr;
P=M&mgr;v+N&rgr;v
2
wherein &Dgr;P is the differential between the pressure at the inlet side and the outlet side of the particulate filter, i.e., the pressure loss in the particulate filter, v is the flow velocity of the exhaust gas flowing through the particulate filter, &mgr; is the viscosity of the exhaust gas, and &rgr; is the density of the exhaust gas. The coefficients M and N become larger as the quantity of the deposited fine exhaust particles becomes larger. More specifically, M or N is substantially a linear function of the deposited quantity ML, and when the deposited quantity is beyond a certain value, the ratio of change of M, N relative to the deposited quantity ML is reduced. The ratio changes before and after the certain value because the pressure loss in the particulate filter is initially increased according to the ratio of fine pores filled with fine exhaust particles to the fine pores in the particulate filter. Then, once almost all the pores are filled with fine exhaust particles, the pressure loss should change based on the thickness of the layer of deposited fine exhaust particles. The present invention is based on the findings.
According to a first aspect of the invention, an exhaust gas cleaning device for an internal combustion engine with a particulate filter provided in an exhaust path for capturing fine exhaust particles includes a differential pressure detecting means for detecting a differential between the pressure at the inlet side and the outlet side of the particulate filter, a flow velocity detecting means for detecting a flow velocity of an exhaust gas flowing through the particulate filter, and a recycling determining means for determining whether or not to recycle the particulate filter according to a determination formula for determining a value of a quantity of fine exhaust particles deposited in the particulate filter based on the detected differential pressure and flow velocity. The determination formula is equivalent to the following formula:
&Dgr;
P≧M&mgr;v+N&rgr;v
2
wherein &Dgr;P is the differential pressure, v is the flow velocity, &mgr; is the viscosity of the exhaust gas flowing through the particulate filter, &rgr; is the density of the exhaust gas, and M and N are constants. When the formula is satisfied, the particulate filter is allowed to be recycled.
As described above, in relation to the exhaust gas flow in the particulate filter, &Dgr;P≧M&mgr;v+N&rgr;v
2
is established, and therefore when M and N are obtained for a reference deposited quantity, the value of the deposited quantity of the fine exhaust particles can accurately be determined based on the determination formula. In this way, the size of data to be stored is not as large as a map.
According to a second aspect of the invention, in the configuration according to the first aspect, the recycling determining means allows the deposited quantity to be calculated by the following determination formula:
ML=[&Dgr;P
−(
A&mgr;v+C&rgr;v
2
)]/(
B&mgr;v+D&rgr;v
2
),
wherein ML is the deposited quantity, A, B, C, and D are constants, and the determination formula is used to compare the value of the calculated deposited quantity and a predetermined deposited quantity.
As described above, M and N are a linear function of the deposited quantity ML, and therefore the above calculation formula for ML is established in the model formula:
&Dgr;
P=M&mgr;v+N&rgr;v
2
so that the deposited quantity of the fine exhaust particles is objectively available.
According to a third aspect of the invention, in the configuration according to the second aspect, the recycling determining means stores two calculation formulas for the deposited quantity having different values for the constants A, B, C, and D, one calculation formula is adapted to a deposited quantity in a range equal to or less than a predetermined reference value, while the other formula is adapted to a deposited quantity within a range equal to or more than the reference value, and

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