Exhaust gas purification system for internal combustion engine
First Claim
1. A system for purifying exhaust gas of an internal combustion engine, including:
- a NOx absorber installed in an exhaust system of the engine which absorbs NOx in exhaust gas generated by the engine in a lean environment and desorbs to reduce the absorbed NOx in a rich environment;
vehicle driving condition detecting means for detecting a driving condition of a vehicle on which the engine is mounted; and
fuel cutoff determining means for determining whether a condition for fuel cutoff, in which supply of fuel to the engine is cut off, is met based on at least the detected driving condition of the vehicle;
wherein the improvement comprises;
rich fuel mixture supplying means for supplying a fuel mixture richer than a stoichiometric fuel mixture to the engine for a first period if the condition for fuel cutoff is met when a fuel mixture leaner than the stoichiometric fuel mixture is supplied to the engine; and
fuel cutoff conducting means for conducting the fuel cutoff upon after the supply of rich fuel mixture to the engine has been terminated.
1 Assignment
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Accused Products
Abstract
A system for purifying exhaust gas of an internal combustion engine having a NOx reduction catalyst (NOx absorber) installed in the exhaust system of the engine which absorbs NOx in the exhaust gas generated by the engine in a lean environment where a lean fuel mixture is supplied and desorbs to reduce the absorbed NOx in a rich environment where a rich mixture is supplied. In the system, the rich fuel mixture is supplied for a period immediately before cutoff. With the arrangement, the NOx reduction catalyst desorbs the absorbed NOx and is regenerated to absorb NOx sufficiently. At the same time, the NOx reduction catalyst is regenerated from sulfur poisoning, thereby preventing the NOx purification efficiency from being degraded.
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Citations
23 Claims
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1. A system for purifying exhaust gas of an internal combustion engine, including:
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a NOx absorber installed in an exhaust system of the engine which absorbs NOx in exhaust gas generated by the engine in a lean environment and desorbs to reduce the absorbed NOx in a rich environment; vehicle driving condition detecting means for detecting a driving condition of a vehicle on which the engine is mounted; and fuel cutoff determining means for determining whether a condition for fuel cutoff, in which supply of fuel to the engine is cut off, is met based on at least the detected driving condition of the vehicle; wherein the improvement comprises; rich fuel mixture supplying means for supplying a fuel mixture richer than a stoichiometric fuel mixture to the engine for a first period if the condition for fuel cutoff is met when a fuel mixture leaner than the stoichiometric fuel mixture is supplied to the engine; and fuel cutoff conducting means for conducting the fuel cutoff upon after the supply of rich fuel mixture to the engine has been terminated. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of purifying exhaust gas of an internal combustion engine having a NOx absorber installed in an exhaust system of the engine which absorbs NOx in exhaust gas generated by the engine in a lean environment and desorbs to reduce the absorbed NOx in a rich environment;
including the steps of; detecting a driving condition of a vehicle on which the engine is mounted; and determining whether a condition for fuel cutoff in which supply of fuel to the engine is cut off, is met based on at least the detected driving condition of the vehicle; wherein the improvement comprises the steps of; supplying a fuel mixture richer than a stoichiometric fuel mixture to the engine for a first period if the condition for fuel cutoff is met when a fuel mixture leaner than the stoichiometric fuel mixture is supplied to the engine; and conducting the fuel cutoff upon after the supply of rich fuel mixture to the engine has been terminated. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A computer program embodied on a computer-readable medium for purifying exhaust gas of an internal combustion engine having a NOx absorber installed in an exhaust system of the engine which absorbs NOx in exhaust gas generated by the engine in a lean environment and desorbs to reduce the absorbed NOx in a rich environment;
including the steps of; detecting a driving condition of a vehicle on which the engine is mounted; and determining whether a condition for fuel cutoff in which supply of fuel to the engine is cut off, is met based on at least the detected driving condition of the vehicle; wherein the improvement comprises the steps of; supplying a fuel mixture richer than a stoichiometric fuel mixture to the engine for a first period if the condition for fuel cutoff is met when a fuel mixture leaner than the stoichiometric fuel mixture is supplied to the engine; and conducting the fuel cutoff upon after the supply of rich fuel mixture to the engine has been terminated.
Specification