Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2003-06-06
2004-01-27
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S274000, C060S285000, C060S296000, C060S297000
Reexamination Certificate
active
06681566
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application Nos. 2000-00434 filed on Mar. 29, 2000 and 2000-04433 filed on Nov. 10, 2000 including the specification, drawings and abstract are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an exhaust purifying method and apparatus of an internal combustion engine. More particularly, the invention relates to an exhaust purifying method and apparatus capable of switching an exhaust gas flow such that the exhaust gas flows through a filter of the purifying apparatus alternately from the exhaust upstream side and exhaust downstream side.
2. Description of Related Art
In diesel engines, a particulate filter is provided in an exhaust passage of the engine in order to remove particulates such as soot contained in the exhaust gas. The particulates in the exhaust gas are temporarily trapped on the particulate filter and then ignited and burned so as to restore the particulate filter. However, the particulates trapped on the particulate filter are not ignited at a high temperature of about 600° C. or more, although the exhaust gas temperature of the diesel engine is normally considerably lower than 600° C. Accordingly, it is difficult to ignite the particulates trapped on the particulate filter with the exhaust gas heat. In order to ignite the particulates trapped on the particulate filter with the exhaust gas heat, it is necessary to enable the particulates to be ignited at a low temperature.
It is known that a particulate filter having a catalyst supported thereon can reduce the ignition temperature of the particulates. A variety of particulate filters are known which have a catalyst supported thereon in order to reduce the ignition temperature of the particulates.
For example, Japanese Patent Publication No. HEI 7-106290 discloses a particulate filter having a mixture of a platinum group metal and an alkaline earth metal oxide supported thereon. In this particulate filter, particulates are ignited at a relatively low temperature of approximately 350° C. to 400° C., and then burned continuously.
In diesel engines, the exhaust gas temperature reaches 350° C. to 400° C. under a high load. Accordingly, in the aforementioned particulate filter, the particulates can seemingly be ignited and burned with the exhaust gas heat under a high load. Actually, however, the particulates are not always ignited even when the exhaust gas temperature reaches 350° C. to 400° C. Moreover, even if the particulates are ignited, only a part of the particulates is burned, and a large amount of particulates is left unburned.
In other words, if the exhaust gas contains a small amount of particulates, the amount of particulates that adhere to the particulate filter is small. In such a case, the particulates on the particulate filter are ignited when the exhaust gas temperature reaches 350° C. to 400° C., and then burned continuously.
However, if the exhaust gas contains a large amount of particulates, additional particulates are deposited on the particulates adhering to the particulate filter before the latter particulates have been burned completely. As a result, the particulates are deposited on the particulate filter in a laminated manner. In such a case, a part of the particulates that is likely to be in contact with oxygen is burned, but the remaining particulates that are less likely to be in contact with oxygen are not burned, and a large amount of particulates are left unburned. Therefore, when the exhaust gas contains a large amount of particulates, a large amount of particulates continues to be deposited on the particulate filter.
If a large amount of particulates is deposited on the particulate filter, these deposited particulates gradually become less likely to be ignited and burned. The reason for this is considered because, while the particulates are being deposited, carbon in the particulates changes to a substance that is less likely to be burned, such as graphite or the like. Actually, if a large amount of particulates is continuously deposited on the particulate filter, the deposited particulates are not ignited at a low temperature of 350° C. to 400° C. A high temperature of 600° C. or more is required in order to ignite the deposited particulates. In diesel engines, however, the exhaust gas temperature does not normally reach a high temperature of 600° C. or more. Accordingly, if a large amount of particulates is continuously deposited on the particulate filter, it becomes difficult to ignite the deposited particulates with the exhaust gas heat.
Moreover, when the deposited particles are burned, ashes, i.e., the matter left after the particulates have been burned, agglomerate into a large mass, resulting in clogging of the pores in the particulate filter. The number of clogged pores is gradually increased with time, so that pressure loss of the exhaust gas flow in the particulate filter is gradually increased. As the pressure loss of the exhaust gas flow is increased, the engine output is reduced, which also necessitates early replacement of the particulate filter with a new one.
Thus, once a large amount of particulates has been deposited in a laminated manner, this causes various problems as described above. Therefore, it is necessary to prevent a large amount of particulates from being deposited in a laminated manner, in view of the balance between the amount of particulates contained in the exhaust gas and the amount of particulates that can be burned on the particulate filter.
The aforementioned problems cannot be avoided by such a continuous combustion process that a conventional exhaust purifying filter having a catalyst thereon is merely provided in an exhaust pipe and that exhaust purification relies on the operation state of the internal combustion engine.
Therefore, by enabling an exhaust gas flow to be switched such that the exhaust gas flows through a filter of a purifying apparatus alternately from the exhaust upstream side and downstream side in order to enable continuous combustion of the particulates as much as possible, the particulates are deposited on both sides of the filter, whereby the particulate deposition amount per unit area can be reduced. Moreover, switching of the exhaust gas flow enables the depositing particles to be stirred and scattered. Furthermore, if a NOx absorbent is provided for a filter base material, NOx in the exhaust gas can also be purified.
In the case where the NOx absorbent is provided for the filter base material in order to simultaneously purify NOx, exhaust gas at a rich air-fuel ratio must be intermittently fed to the filter (this is called “rich spike”) so as to discharge NOx from the NOx absorbent for reduction. This is because of limited NOx-absorbing ability of the NOx absorbent. On the other hand, in order to switch the direction of the exhaust gas flowing through the filter as described above for the purpose of facilitating continuous combustion of the particulates, a switch valve must be provided within the exhaust pipe. However, the structure of the switch valve necessitates the exhaust gas to bypass the filter during switching of the exhaust gas flow.
Accordingly, in the case where the timing of conducting the rich spike matches the timing of switching the exhaust gas flow by the switch valve, the exhaust gas at a rich air-fuel ratio and containing a large amount of reducing agent may possibly be discharged without passing through the filter.
In the case of using the exhaust purifying filter having the NOx absorbent at the filter base material in order to simultaneously remove the particulates and purify NOx, a system for feeding the exhaust gas so as to bypass the filter is possible in order to prevent the particulates from being deposited on the filter in a preset amount or more when the particulate oxidation capability of the filter is not enough, or may possibly be degraded due to a low temperature of the exhaust gas (e.g., during decelerating operation).
Even in such a system, if th
Asanuma Takamitsu
Hirota Shinya
Itoh Kazuhiro
Kimura Koichi
Nakatani Koichiro
Denion Thomas
Nguyen Tu M.
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
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