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1. US20130017121 - Exhaust purification system of internal combustion engine

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[ EN ]

Claims

1. An exhaust purification system of an internal combustion engine comprising:
a hydrocarbon feed valve for feeding hydrocarbons arranged in an engine exhaust passage,
an exhaust purification catalyst for reacting NO X contained in exhaust gas and reformed hydrocarbons arranged in the engine exhaust passage downstream of the hydrocarbon feed valve,
a downstream side air-fuel ratio sensor for detecting an air-fuel ratio of the exhaust gas arranged in the engine exhaust passage downstream of the exhaust purification catalyst,
precious metal catalysts carried on an exhaust gas flow surface of the exhaust purification catalyst,
a basic exhaust gas flow surface part formed around the precious metal catalysts, and
an electronic control unit, wherein the electronic control unit is configured to control a vibration of a concentration of hydrocarbons flowing into the exhaust purification catalyst within a predetermined range of amplitude and within a predetermined range of period, and is configured to control the vibration period of the hydrocarbon concentration longer than the predetermined range of period, wherein
when the electronic control unit controls the vibration of the concentration of hydrocarbons flowing into the exhaust purification catalyst within the predetermined range of amplitude and within the predetermined range of period, a reducing intermediate containing nitrogen and hydrocarbons is produced on the precious metal catalysts and held on the basic exhaust gas flow surface part, the NO X contained in the exhaust gas is chemically reduced by the reducing intermediate held on the basic exhaust gas flow surface part, and the exhaust purification catalyst has a property of chemically reducing the NO X that is contained in the exhaust gas without storing, or with storing a fine amount of, nitrates in the basic exhaust gas flow surface part,
when the electronic control unit controls the vibration period of the hydrocarbon concentration longer than the predetermined range, the exhaust purification catalyst has a property of being increased in a storage amount of NO X that is contained in the exhaust gas and
the concentration of hydrocarbons that flow into the exhaust purification catalyst is made to vibrate within the predetermined range of period by control of an injection period of hydrocarbons from the hydrocarbon feed valve, and the amplitude of a change of concentration of hydrocarbons that flow into the exhaust purification catalyst is made to become within the predetermined range of amplitude by control of an injection amount of hydrocarbons from the hydrocarbon feed valve based on an output signal of the downstream side air-fuel ratio sensor.
2. The exhaust purification system of the internal combustion engine as claimed in claim 1, wherein in the exhaust purification catalyst, NO X contained in exhaust gas and reformed hydrocarbons react to produce the reducing intermediate containing nitrogen and hydrocarbons, and wherein the injection period of the hydrocarbons is a period necessary for continued production of the reducing intermediate.
3. The exhaust purification system of the internal combustion engine as claimed in claim 1, wherein the precious metal catalysts are comprised of platinum (Pt) and at least one of rhodium (Rh) or palladium (Pd).
4. The exhaust purification system of the internal combustion engine as claimed in claim 1, wherein a basic layer containing an alkali metal, an alkali earth metal, a rare earth, or a metal that donates electrons to NO X is formed on the exhaust gas flow surface of the exhaust purification catalyst and wherein a surface of the basic layer forms the basic exhaust gas flow surface part.
5. The exhaust purification system of the internal combustion engine as claimed in claim 1, wherein when the injection period of hydrocarbons from the hydrocarbon feed valve is controlled so that the concentration of hydrocarbons that flow into the exhaust purification catalyst vibrates within the predetermined range of period, the air-fuel ratio that is detected by the downstream side air-fuel ratio sensor also vibrates, and when a rich side peak air-fuel ratio that is detected by the downstream side air-fuel ratio sensor is at a lean side from a predetermined air-fuel ratio, the injection amount of hydrocarbons from the hydrocarbon feed valve is increased, while when the rich side peak air-fuel ratio that is detected by the downstream side air-fuel ratio sensor is at a rich side from the predetermined air-fuel ratio, the injection amount of hydrocarbons from the hydrocarbon feed valve is decreased.
6. The exhaust purification system of the internal combustion engine as claimed in claim 1, wherein further comprising an upstream air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas arranged in the engine exhaust passage upstream of the hydrocarbon feed valve, wherein the injection amount of hydrocarbons from the hydrocarbon feed valve is controlled so that the amplitude of the change in concentration of hydrocarbons that flow into the exhaust purification catalyst become within the predetermined range of amplitude on the basis of both an output signal of the upstream side air-fuel ratio sensor and the output signal of the downstream side air-fuel ratio sensor.
7. The exhaust purification system of the internal combustion engine as claimed in claim 6 wherein
when the injection period of hydrocarbons from the hydrocarbon feed valve is controlled so that the concentration of hydrocarbons that flow into the exhaust purification catalyst is made to vibrate within the predetermined range of period, the air-fuel ratio that is detected by the downstream side air-fuel ratio sensor also vibrates,
when the air-fuel ratio that is detected by the upstream side air-fuel ratio sensor is at a lean side from a predetermined air-fuel ratio, the injection amount of hydrocarbons from the hydrocarbon feed valve is increased, while when the air-fuel ratio that is detected by the upstream side air-fuel ratio sensor is at a rich side from the predetermined air-fuel ratio, the injection amount of hydrocarbons from the hydrocarbon feed valve is decreased, and
when a rich side peak air-fuel ratio that is detected by the downstream side air-fuel ratio sensor is at a lean side from a predetermined air-fuel ratio, the injection amount of hydrocarbons from the hydrocarbon feed valve is increased, while when the rich side peak air-fuel ratio that is detected by the downstream side air-fuel ratio sensor is at a rich side from the predetermined air-fuel ratio, the injection amount of hydrocarbons from the hydrocarbon feed valve is decreased.
8. The exhaust purification system of the internal combustion engine as claimed in claim 6, wherein an amount of fuel that is fed into an engine combustion chamber is controlled based on the output signal of the upstream side air-fuel ratio sensor so that the air-fuel ratio of the exhaust gas which is exhausted from the engine is made to become a predetermined air-fuel ratio.
9. The exhaust purification system of the internal combustion engine as claimed in claim 8, wherein when the injection amount of hydrocarbons from the hydrocarbon feed valve is controlled based on both the output signal of the upstream side air-fuel ratio sensor and the output signal of the downstream side air-fuel ratio sensor so that the amplitude of the change in concentration of hydrocarbons that flow into the exhaust purification catalyst becomes within the predetermined range of amplitude of the air-fuel ratio, a diagnosis of trouble of the exhaust purification system is performed based on the output signal of the downstream side air-fuel ratio sensor.
10. The exhaust purification system of the internal combustion engine as claimed in claim 9, wherein
when the injection period of hydrocarbons from the hydrocarbon feed valve is controlled so that the concentration of hydrocarbons that flow into the exhaust purification catalyst vibrates within the predetermined range of period, the air-fuel ratio that is detected by the downstream side air-fuel ratio sensor also vibrates,
when a rich side peak air-fuel ratio that is detected by the downstream side air-fuel ratio sensor becomes a lean side from a predetermined air-fuel ratio, an injection time of hydrocarbons is made to increase in order to increase the injection amount of hydrocarbons from the hydrocarbon feed valve, and
when a rate of increase of the injection time of hydrocarbons exceeds a predetermined rate at this time, the electronic control unit determines that the hydrocarbon feed valve is clogged.
11. The exhaust purification system of the internal combustion engine as claimed in claim 10, wherein when the injection period of hydrocarbons from the hydrocarbon feed valve is controlled so that the concentration of hydrocarbons that flow into the exhaust purification catalyst vibrate within the predetermined range of period, the air-fuel ratio that is detected by the downstream side air-fuel ratio sensor vibrates to a rich side from a base air-fuel ratio, and the electronic control unit determines if the hydrocarbon feed valve is clogged based on an integrated value of a difference between the air-fuel ratio detected by the downstream side air-fuel ratio sensor and the base air-fuel ratio.
12. The exhaust purification system of the internal combustion engine as claimed in claim 11, wherein when using the integrated value of the difference between the air-fuel ratio detected by the downstream side air-fuel ratio sensor and the base air-fuel ratio as the basis to judge if the hydrocarbon feed valve is clogged, the injection amount of hydrocarbons is made smaller when the injection amount of hydrocarbons is too large to accurately detect the injection amount of hydrocarbons from the hydrocarbon feed valve.
13. The exhaust purification system of the internal combustion engine as claimed in claim 11 wherein when using the integrated value of the difference between the air-fuel ratio detected by the downstream side air-fuel ratio sensor and the base air-fuel ratio as the basis to judge if the hydrocarbon feed valve is clogged, the injection period of hydrocarbons is made longer when the injection period of hydrocarbons is too short to accurately detect the injection amount of hydrocarbons from the hydrocarbon feed valve.
14. The exhaust purification system of the internal combustion engine as claimed in claim 13, wherein the injection period of the hydrocarbons is 0.3 second to 5 seconds.