Power plants – Internal combustion engine with treatment or handling of... – By sorber or mechanical separator
Reexamination Certificate
2002-12-11
2004-03-23
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By sorber or mechanical separator
C060S295000, C060S297000, C060S285000
Reexamination Certificate
active
06708487
ABSTRACT:
This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2001-378946 filed in JAPAN on Dec. 12, 2001, which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust emission control device suitable for a diesel engine.
2. Description of the Related Art
An exhaust gas exhausted from a diesel engine contains particulates (soot) mainly composed of carbon, and various techniques for suppressing this soot to be exhausted to the atmosphere have been developed.
As one of those techniques, an exhaust emission control device of the continuous regeneration type is well-known in which an oxidation catalyst and a diesel particulate filter (DPF) are disposed in succession from the upstream side in an exhaust pipe of the diesel engine.
In this exhaust emission control device, NO in the exhaust gas is oxidized by the oxidation catalyst to produce NO
2
(2NO+O
2
→2NO
2
), and the soot (carbon: C) captured in the DPF is oxidized by NO
2
produced by the oxidation catalyst (NO
2
+C→NO+CO, 2NO
2
+C→2NO+CO
2
). In this exhaust emission control device, NO contained greatly in the exhaust gas is oxidized and converted into NO
2
, which has a high function as an oxidant, and the soot is combusted at relatively low exhaust gas temperatures owing to this oxidation function of NO
2
.
Thereby, it is possible to remove the deposited soot, and regenerate the DPF continuously, utilizing the temperature of the exhaust gas itself, without the use of other heating apparatuses such as an electric heater or a burner.
The conventional exhaust emission control device can combust and remove the soot at relatively low exhaust gas temperatures owing to catalytic action. Thus, its exhaust emission control function depends on the oxidizing ability of the oxidation catalyst. Since this oxidizing ability typically depends on the temperature of the exhaust gas surrounding the oxidation catalyst, the soot is not fully removed and the residual soot is accumulated on the DPF when the exhaust gas temperature is below a predetermined temperature that is required for the soot combustion. This occurs in a low load area of the engine.
If the soot is excessively deposited on the DPF, there is a risk that the engine output is decreased and also the DPF melts away due to abnormally high temperatures during the soot combustion. Therefore, it is required to remove the deposited soot by any means, and such methods for removing the soot include a forced regeneration method and a continuous regeneration assist method, which we reconventionally developed and adopted.
The forced regeneration method involves elevating the exhaust gas temperature up to a temperature range required for O
2
combustion of the soot due to post injection or the like and forcedly combusting the soot by O
2
. However, this method is inferior in the fuel consumption because excess fuel is consumed, and must be improved for the practical use.
The continuous regeneration assist method involves assisting a continuous regeneration function by elevating the exhaust gas temperature to the maximum conversion temperature range at which the NO
2
conversion efficiency of oxidation catalyst is at peak by an exhaust throttle, and exhibiting the catalytic ability of oxidation catalyst to the maximum. However, with this method, since a variation in the exhaust gas temperature is gentle, it takes a long time to elevate the temperature, greatly aggravating the fuel consumption, when the exhaust gas temperature greatly falls below the maximum conversion temperature range.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an exhaust emission control device that can regenerate a filter without greatly aggravating the fuel consumption.
An exhaust emission control device of the present invention has a filter disposed in an exhaust passage of an engine for capturing particulates in an exhaust gas, and a catalyst disposed in the exhaust passage on the upstream side of the filter for converting NO in the exhaust gas into NO
2
, in which the particulates deposited on the filter are combusted by NO
2
converted by the catalyst, thereby controlling the exhaust emission of the engine.
In order to achieve the above object, the exhaust emission control device comprises deposited amount detecting means for detecting a deposited amount of particulates deposited on the filter, operating state detecting means for detecting an operating state of the engine, temperature sensing means for sensing the temperature of the catalyst or the exhaust gas temperature on the upstream side of the filter, regeneration assist means for controlling the exhaust gas temperature or the temperature of the catalyst to enhance the conversion efficiency of the catalyst into NO
2
, forced regeneration means for controlling the exhaust gas temperature or the temperature of the filter to be higher than the temperature that enhances the conversion efficiency of the catalyst into NO
2
, and control means for activating the regeneration assist means, if it is determined that a specific operating state involving incomplete combustion of particulates by the NO
2
is continued for a predetermined period or more as a first determination condition on the basis of the detected information by the operating state detecting means, or activating the forced regeneration means, if it is determined that the deposited amount of particulates detected by the deposited amount detecting means exceeds a predetermined value as a second determination condition, wherein the control means activates either the forced regeneration means or the regeneration assist means in accordance with the temperature sensed by the temperature sensing means, when it is determined that the first and second determination conditions are established at the same time.
In this exhaust emission control device, the control means activates either the forced regeneration means or the regeneration assist means in accordance with the temperature sensed by the temperature sensing means, when it is determined that the first determination condition for activating the regeneration assist means and the second determination condition for activating the forced regeneration means are established at the same time.
When the first and second determination conditions are established at the same time, either the regeneration assist means or the forced regeneration means is activated, so that an optimal control can be effected in accordance with an engine operating situation. Namely, an effective filter regenerating process can be made.
It is desirable that the control means activates the regeneration assist means if the temperature sensed by the temperature sensing means is higher than or equal to a predetermined temperature that is lower than the temperature to enhance the conversion efficiency of the catalyst into NO
2
, or activates the forced regeneration means if the temperature sensed by the temperature sensing means is below the predetermined temperature, when it is determined that the first and second determination conditions are established at the same time.
Herein, when the first and second determination conditions are established at the same time, and if the temperature sensed by the temperature sensing means is higher than or equal to the predetermined temperature that is lower than the temperature to enhance the conversion efficiency of the catalyst into NO
2
, the control means activates the regeneration assist means, because there is a small difference between the exhaust gas temperature or the temperature of the catalyst and the temperature to enhance the conversion efficiency of the catalyst into NO
2
. Thereby, it takes a shorter time to control (elevate) the temperature, and it is possible to continuously regenerate the particulates owing to catalytic action of the catalyst, with reduced consumption energy.
Moreover, when the control means activates the forced regeneration means if the temp
Morimoto Manabu
Oohashi Kazuya
Terada Mikio
Denion Thomas
Mitsubishi Jidosha Kogyo Kabushiki Kaisha
Tran Diem
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