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DE-102020129835-B4 - EXHAUST ENGINE CLEANING SYSTEM

DE102020129835B4DE 102020129835 B4DE102020129835 B4DE 102020129835B4DE-102020129835-B4

Abstract

Exhaust gas purification system of an internal combustion engine, comprising: a catalyst (20) arranged in an outlet passage and capable of storing oxygen; and an air-fuel ratio control device (31) configured to control the air-fuel ratio of incoming exhaust gas flowing into the catalyst (20), wherein the catalyst (20) comprises a precious metal and the precious metal has a property that a vapor pressure decreases at a predetermined temperature when it is oxidized, In the event that the temperature of the catalyst (20) is greater than or equal to a threshold temperature or a temperature increase of the catalyst (20) is predicted, the air-fuel ratio control device (31) is configured to make the air-fuel ratio of the incoming exhaust gas leaner than a stoichiometric air-fuel ratio, so that an oxygen storage quantity of the catalyst (20) becomes greater than or equal to an upper reference quantity, and the threshold temperature is set at a temperature at which the vapor pressure of the precious metal does not increase when local heat generation of the catalyst (20) occurs due to the supply of oxygen.

Inventors

  • Hiroyoshi UEDA
  • Kazuhiro Umemoto

Assignees

  • TOYOTA JIDOSHA KABUSHIKI KAISHA

Dates

Publication Date
20260513
Application Date
20201112
Priority Date
20191216

Claims (10)

  1. Exhaust gas purification system of an internal combustion engine, comprising: a catalyst (20) which is arranged in an exhaust passage and is capable of storing oxygen; and an air-fuel ratio control device (31) configured to control the air-fuel ratio of incoming exhaust gas flowing into the catalyst (20), wherein the catalyst (20) comprises a noble metal and the noble metal has the property that its vapor pressure decreases at a predetermined temperature when oxidized, in the event that a temperature of the catalyst (20) is greater than or equal to a threshold temperature or a temperature increase of the catalyst (20) is predicted, the air-fuel ratio control device (31) is configured to make the air-fuel ratio of the incoming exhaust gas leaner than a stoichiometric air-fuel ratio, such that an oxygen storage quantity of the catalyst (20) becomes greater than or equal to an upper reference quantity, and the threshold temperature is set at a temperature at which the vapor pressure of the noble metal does not increase when oxygen is supplied a local heat generation of the catalyst (20) occurs.
  2. Exhaust gas purification system of the internal combustion engine Claim 1 , further comprising a NOx cleaning device (23) which is arranged in the outlet passage on a downstream side of the catalyst (20) in an exhaust gas flow direction and is able to remove the NOx flowing out of the catalyst (20).
  3. Exhaust gas purification system of the internal combustion engine after Claim 2 , wherein the NOx cleaning device (23) can store oxygen, and in the case that the temperature of the catalyst (20) is greater than or equal to the threshold temperature or a temperature increase of the catalyst (20) is predicted, the air-fuel ratio control device (31) is configured to make the air-fuel ratio of the incoming exhaust gas richer than the stoichiometric air-fuel ratio, so that an oxygen storage quantity of the NOx cleaning device (23) becomes less than or equal to a lower reference quantity, which is less than the upper reference quantity, and then to make the air-fuel ratio of the incoming exhaust gas leaner than the stoichiometric air-fuel ratio, so that the oxygen storage quantity of the catalyst tors (20) becomes greater than or equal to the upper reference set.
  4. Exhaust gas purification system of the internal combustion engine after Claim 2 , further comprising a fuel supply valve (47) which supplies fuel to the outlet passage between the catalyst (20) and the NOx cleaning device (23), wherein the NOx cleaning device (23) can store oxygen, and the air-fuel ratio control device (31) is configured to control the fuel supply valve (47), and in the event that the temperature of the catalyst (20) is greater than or equal to the threshold temperature or a temperature increase of the catalyst (20) is predicted, to supply fuel through the fuel supply valve (47) such that an oxygen storage quantity of the NOx cleaning device (23) becomes less than or equal to a lower reference quantity which is less than the upper reference quantity.
  5. Exhaust gas purification system of an internal combustion engine, comprising: a catalyst (20) which is arranged in an exhaust passage and is capable of storing oxygen; and an air-fuel ratio control device (31) configured to control the air-fuel ratio of incoming exhaust gas flowing into the catalyst (20), wherein the catalyst (20) comprises a noble metal and the noble metal has the property that its vapor pressure increases at a predetermined temperature when oxidized, in the event that a temperature of the catalyst (20) is greater than or equal to a threshold temperature or a temperature increase of the catalyst (20) is predicted, the air-fuel ratio control device (31) is configured to make the air-fuel ratio of the incoming exhaust gas richer than a stoichiometric air-fuel ratio, such that an oxygen storage quantity of the catalyst (20) becomes less than or equal to a lower reference quantity, and the threshold temperature is set at a temperature at which the vapor pressure of the noble metal does not increase when, due to an influx of HC a local heat generation of the catalyst (20) occurs.
  6. Exhaust gas purification system of the internal combustion engine after Claim 5 , further comprising an HC cleaning device (23) which is arranged in the outlet passage on a downstream side of the catalyst (20) in an exhaust gas flow direction and is able to remove HC flowing out of the catalyst (20).
  7. Exhaust gas purification system of the internal combustion engine after Claim 6 , wherein the HC cleaning device (23) can store oxygen, and in the event that the temperature of the catalyst (20) is greater than or equal to the threshold temperature or a temperature increase of the catalyst (20) is predicted, the air-fuel ratio control device (31) is configured to make the air-fuel ratio of the incoming exhaust gas leaner than the stoichiometric air-fuel ratio, so that an oxygen storage quantity of the HC cleaning device (23) becomes greater than or equal to an upper reference quantity which is greater than the lower reference quantity, and then to make the air-fuel ratio of the incoming exhaust gas richer than the stoichiometric air-fuel ratio, so that an oxygen storage quantity of the catalyst (20) becomes less than or equal to the lower reference quantity.
  8. Exhaust gas purification system of the internal combustion engine after Claim 6 , further comprising an air supply device (100) which supplies air to the outlet passage between the catalyst (20) and the HC cleaning device (23), wherein the HC cleaning device (23) can store oxygen, and the air-fuel ratio control device (31) is configured to control the air supply device (100), and in the event that the temperature of the catalyst (20) is greater than or equal to the threshold temperature or a temperature increase of the catalyst (20) is predicted, supplying air through the air supply device (100) so that an oxygen storage quantity of the HC cleaning device (23) becomes greater than or equal to an upper reference quantity which is greater than the lower reference quantity.
  9. Exhaust gas purification system of an internal combustion engine, comprising: a catalyst (20) arranged in an exhaust passage and capable of storing oxygen; and an air-fuel ratio control device (31) configured to control an atmosphere of the catalyst (20), wherein the catalyst (20) comprises a noble metal and the noble metal has the property that a vapor pressure at a predetermined temperature in a second atmosphere from a reducing atmosphere or an oxidizing atmosphere is lower compared to a first atmosphere from an oxidizing atmosphere or a reducing atmosphere, in the event that a temperature of the catalyst (20) is greater than or equal to a threshold temperature or a temperature increase of the catalyst (20) The air-fuel ratio control device (31) is designed to make the catalyst (20) subject to the second atmosphere, and the threshold temperature is set at a temperature at which the vapor pressure of the precious metal does not increase when local heat generation of the catalyst (20) occurs due to an input of oxygen or HC.
  10. Exhaust gas purification system of the internal combustion engine after Claim 9 , further comprising a downstream catalyst (23) which is arranged in the outlet passage on a downstream side of the catalyst (20) in an exhaust gas flow direction and is capable of storing oxygen, and in the case that the temperature of the catalyst (20) is greater than or equal to the threshold temperature or a temperature increase of the catalyst (20) is predicted, the air-fuel ratio control device (31) is configured to make the downstream catalyst (23) the first atmosphere.

Description

AREA The present invention relates to an exhaust gas purification system for an internal combustion engine. BACKGROUND In the past, it was known to place a catalyst in the exhaust port of an internal combustion engine and to remove the harmful substances from the exhaust gas (HC, NOx, etc.) at the catalyst (e.g., JP 2018 - 9 535 A). However, if oxygen is supplied to the catalyst at a high temperature, oxidation of the precious metal can cause a deterioration of the catalyst. In contrast, if, in the internal combustion engine described in JP 2018-9535A, the catalyst temperature is greater than or equal to a predetermined temperature when the condition for implementing a fuel cut-off control (which stops fuel injection by a fuel injector) is met, then the control to introduce EGR gas instead of fresh air into the catalyst is implemented when the fuel cut-off control is executed. It is assumed that this prevents oxygen from entering the catalyst and thus prevents catalyst degradation. Furthermore, the US 2015 / 0 322 878 A1 A control device for an internal combustion engine, comprising: an upstream catalyst; a downstream catalyst located further downstream in the exhaust flow direction than the upstream catalyst; a downstream means for sensing the air-fuel ratio provided between these catalysts; a means for estimating the storage quantity, which estimates the oxygen storage quantity of the downstream catalyst; and a control device for the air-fuel ratio of the incoming exhaust gas, which controls the air-fuel ratio of the exhaust gas entering the upstream catalyst such that the air-fuel ratio of the exhaust gas reaches a target air-fuel ratio. In a rich-run mode during normal operation, the target air-fuel ratio is set lean when the air-fuel ratio detected by the downstream air-fuel ratio sensing device is rich, and the target air-fuel ratio is set rich when the oxygen storage quantity of the upstream catalyst is equal to or greater than an upstream reference storage quantity. If the oxygen storage quantity of the downstream catalyst is equal to or less than a downstream lower limit storage quantity that is less than the maximum storage quantity, then the target air-fuel ratio is set lean, so that the air-fuel ratio of the exhaust gas flowing from the upstream catalyst becomes lean. Further relevant state of the art can be found in the following non-patent literature: CARRILLO, Cristihan [et al.]: regenerative trapping: How Pd improves the durability of Pt diesel oxidation catalysts. In: Applied Catalysis B: Environmental, Vol. 218, 2017, pp. 581-590. ISSN 0926-3373 . SUMMARY [TECHNICAL PROBLEM] However, to implement the above control, a design for recirculating the EGR gas from an exhaust port to an intake port is essential, and it is necessary to delay the start of the fuel cut-off control to effect this EGR gas recirculation. Furthermore, oxygen can flow into the catalyst even at a time other than the fuel cut-off control, for example, when the internal combustion engine is stopped. In addition, at high catalyst temperatures, the catalyst may degrade, depending on the properties of its precious metal, due to exhaust gas with a richer air-fuel ratio than the stoichiometric air-fuel ratio entering the catalyst. Therefore, in view of the above problem, the present invention is based on the objective of providing an exhaust gas purification system for an internal combustion engine that is capable of effectively preventing deterioration of a catalyst. [SOLUTION TO THE PROBLEM] The above problem is solved by the subject matter of the independent claims. Advantageous embodiments of the invention are the subject matter of the subsequent dependent claims. The following are explanatory aspects of the present revelation. (1) Exhaust gas purification system of an internal combustion engine, comprising: a catalyst arranged in an exhaust port a catalyst that is capable of storing oxygen; and an air-fuel ratio control device configured to control the air-fuel ratio of incoming exhaust gas flowing into the catalyst, wherein the catalyst comprises a noble metal and the noble metal has the property of having a vapor pressure that decreases at a predetermined temperature when oxidized, and in the event that a temperature of the catalyst is greater than or equal to a threshold temperature or a temperature increase of the catalyst is predicted, the air-fuel ratio control device is configured to make the air-fuel ratio of the incoming exhaust gas leaner than a stoichiometric air-fuel ratio, so that an oxygen storage quantity of the catalyst becomes greater than or equal to an upper reference quantity. (2) Exhaust gas purification system of an internal combustion engine according to (1), further comprising a NOx cleaning device which is arranged in the exhaust passage on a downstream side of the catalyst in an exhaust gas flow direction and is able to remove the NOx flowing out of the catalyst. (3) Exhaust gas purification system