Engine exhaust gas control system having NOx catalyst
First Claim
1. A control system for an internal combustion engine, comprising:
- air-fuel ratio control means for normally controlling an air-fuel ratio of air-fuel mixture supplied to the internal combustion engine to a lean side with respect to a stoichiometric ratio for a lean mixture combustion, and temporarily controlling the air-fuel ratio to a rich side with respect to the stoichiometric air-fuel ratio;
NOx catalyst means for occluding Nox in an exhaust gas exhausted at the time of the lean mixture combustion and releasing the occluded NOx from the NOx catalyst by temporarily controlling the air-fuel ratio to the rich side for a rich mixture combustion; and
rich time setting means for setting a rich time for the rich mixture combustion in accordance with an engine operating state and an NOx purification rate by the NOx catalyst.
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Accused Products
Abstract
In an engine exhaust system, an NOx catalyst for occluding NOx in a state of the lean air-fuel ratio and reducing the occluded NOx in the state of the rich air-fuel ratio. A CPU sets a target air-fuel ratio of a mixture supplied to an engine to the lean side with respect to the stoichiometric air-fuel ratio for the lean mixture combustion. The CPU sets a rich time for a rich mixture combustion in accordance with the engine operating state and the NOx purification rate in the NOx catalyst. In this moment, the shortest rich time is set within a range in which a desired NOx purification rate by the NOx catalyst is obtained. A three-way catalyst may be arranged upstream of the NOx catalyst. The three-way catalyst carries only a noble metal such as platinum having no oxygen storing capability.
56 Citations
7 Claims
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1. A control system for an internal combustion engine, comprising:
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air-fuel ratio control means for normally controlling an air-fuel ratio of air-fuel mixture supplied to the internal combustion engine to a lean side with respect to a stoichiometric ratio for a lean mixture combustion, and temporarily controlling the air-fuel ratio to a rich side with respect to the stoichiometric air-fuel ratio; NOx catalyst means for occluding Nox in an exhaust gas exhausted at the time of the lean mixture combustion and releasing the occluded NOx from the NOx catalyst by temporarily controlling the air-fuel ratio to the rich side for a rich mixture combustion; and rich time setting means for setting a rich time for the rich mixture combustion in accordance with an engine operating state and an NOx purification rate by the NOx catalyst. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification