Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2000-04-28
2001-12-11
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S274000, C060S285000, C060S297000
Reexamination Certificate
active
06327849
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and a controller for an internal combustion engine wherein nitrogen oxide (NOx) is absorbed by a purifying device provided for an exhaust system.
2. Description of the Related Art
When the air-fuel ratio of the air-fuel mixture supplied to an internal combustion engine is set leaner than the stoichiometric air-fuel ratio and the lean operation is executed, the volume of NOx that is discharged with the exhaust gases tends to increase. Therefore, in a well known conventional technique, a NOx absorbent for absorbing NOx during a lean operation is provided for the exhaust system of an internal combustion engine, and as needed, the absorbed NOx is purified by reduction (e.g., Japanese Patent No. 2,586,739).
The NOx absorbent of the NOx purifying device has the following characteristics: when the air-fuel ratio is set so that a leaner mixture is supplied than one that is theoretically correct, and the oxygen content of the exhaust gases is comparatively high (the exhaust contains a high percentage of NOx; a condition hereinafter referred to as a lean exhaust-gas condition), NOx is absorbed, while when the air-fuel ratio is set so that a richer mixture is supplied than the theoretically correct one and the oxygen content of the exhaust gases is comparatively low (a condition hereinafter referred to as a rich exhaust-gas condition), NOx is discharged. The NOx purifying device is so designed that, during a rich exhaust-gas condition, the NOx released by the NOx absorbent is reduced by HC and CO and is discharged as nitrogen gas, while the HC and CO are oxidized and are discharged as steam and carbon dioxide.
Since the NOx absorbent of the NOx purifying device absorbs not only NOx but also SOx (sulfur oxide), in the absorbent there is a gradual buildup of the sulfur (S) that is contained in fuel. As a result, a problem has arisen because sulfur contamination can drastically reduce the available capacity for the absorption of NOx (for example, an absorption capacity of 80% can be reduced to approximately 20%). But since the SOx absorbed by the NOx absorbent can be discharged therefrom when the NOx absorbent is maintained at a high temperature (600° C. or higher), the volume of the SOx contamination can be reduced by setting a rich air-fuel ratio. However, only when a high-load operation is continuously performed for a comparatively extended period of time can the temperature of the NOx absorbent be elevated so it is equal to or higher than 600° C. Therefore, the operating state wherein an air-fuel ratio rich operation can be performed to remove SOx is actually limited, and SOx can not be satisfactorily purified.
Further, to discharge and reduce the SOx, it is preferable that the temperature of the NOx absorbent be elevated rapidly, within a short period of time. It has confirmed that when the air-fuel ratio of an air-fuel mixture to be supplied to an engine is altered so that it is first leaner and then richer than the stoichiometric air-fuel ratio, and when a short time interval, 3 seconds or less, for example, is allocated for this variation, the temperature of the NOx absorbent can be elevated rapidly, within a short period of time. However, while only a short interval is required for the air-fuel ratio variation, within this short interval a change in the output torque of the engine is also experienced, and is accompanied by the deterioration of the engine's operating performance.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an exhaust gas-purifying apparatus that can, in a short period of time, elevate the temperature of a NOx absorbent to a temperature that is adequate for the discharge of SOx, and that can efficiently remove SOx that has been absorbed by the NOx absorbent.
It is another object of the present invention to provide a controller for an internal combustion engine that can rapidly elevate the temperature of a NOx absorbent and remove SOx quickly, without adversely affecting the operating performance of the engine.
To achieve the above object, according to a first aspect of the invention, an exhaust gas purifying apparatus for the exhaust system of an internal combustion engine, comprises:
nitrogen oxide purifying means for absorbing the nitrogen oxide in exhaust gases in a lean exhaust-gas condition during which the oxygen concentration of the exhaust gas is comparatively high;
deterioration detection means for detecting the deterioration of the nitrogen oxide purifying means;
air-fuel ratio variation means for, when the deterioration of the nitrogen oxide purifying means is detected by the deterioration detection means, varying, during an interval that is set equal to or shorter than a predetermined time, the air-fuel ratio for the air-fuel mixture supplied to the internal combustion engine, and to thus provide an air-fuel ratio that is leaner or richer than a stoichiometric air-fuel ratio; and
deterioration recovery means for, when an elevated temperature attained at the nitrogen oxide purifying means exceeds a deterioration recovery temperature following activation of the air-fuel ratio variation means, performing deterioration recovery by maintaining for an adequate period of time a richer air-fuel ratio than the stoichiometric air-fuel ratio.
The “predetermined time” is an appropriate time period for effecting the elevation of the temperature of the nitrogen oxide purifying means, e.g., three seconds or less. Specifically, when fuel consumption during the air-fuel ratio variation control process is an important factor, it is preferable that the predetermined time be (lean time+rich time), wherein the “lean time,” for setting the air-fuel ratio richer than the stoichiometric air-fuel ratio, is defined as a period of 2 seconds or less, and the “rich time,” for controlling the air-fuel ratio that is richer than the stoichiometric air-fuel ratio, is defined as ½ the lean time or shorter. When rapid elevation of the temperature of the nitrogen oxide purifying means during the air-fuel ratio variation control processing is more important, and especially when a three-way catalyst is positioned immediately downstream of the engine and the nitrogen oxide purifying means is positioned downstream of the three-way catalyst and slightly separated from the engine, it is preferable that substantially the same period be set for the lean time and the rich time.
The “deterioration recovery temperature” is defined as substantially the lowest temperature whereat SOx begins to be discharged from the nitrogen oxide absorbent in the nitrogen oxide purifying means, or is defined as a temperature 50 to 100° C. higher than the lowest temperature, while taking into account the fact that the temperature will be reduced when the air-fuel rich operation is initiated by the deterioration recovery means. Furthermore, in accordance with the degree of deterioration detected by the deterioration detection means, i.e., in accordance with the volume of the SOx accumulated in the nitrogen oxide purifying means at the time the deterioration was detected, the period set for the “deterioration recovery time” is, for example, the time required for the reduction of substantially all the adsorbed SOx.
It is preferable that temperature detection means be provided to actually detect the temperature of the nitrogen oxide purifying means, and that the detected value be employed to determine whether the temperature of the nitrogen oxide purifying means is greater than the deterioration recovery temperature. However, instead of using the temperature detection means, whether the air-fuel ratio variation time of the air-fuel ratio variation means exceeds the predetermined temperature elevation time may be determined to ascertain whether the temperature of the nitrogen oxide purifying means is higher than the deterioration recovery temperature. In this case, an experiment was conducted for a plurality of apparatus
Ohno Hiroshi
Sakanushi Masahiro
Sugiura Kenji
Yagisawa Keiichi
Denion Thomas
Honda Giken Kogyo Kabushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tran Binh
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