Exhaust system of internal combustion engine

Abstract

An exhaust system includes an electronic control unit that is configured to control a turbo bypass valve to be in a fully closed state and control an opening degree of a wastegate valve to a first predetermined opening degree during execution of fuel cut control, and maintain the turbo bypass valve in the fully closed state and control an opening degree of the wastegate valve to a second predetermined opening degree when a boost request is not made for the internal combustion engine at the end of the fuel cut control. An area of inflow of bypass gas on an upstream side end surface of the three-way catalyst when the opening degree of the wastegate valve is controlled to the first predetermined opening degree is in a different position from when the opening degree of the wastegate valve is controlled to the second predetermined opening degree.

What is claimed is: 
     
       1. An exhaust system of an internal combustion engine, the exhaust system comprising:
 a turbocharger that includes a turbine disposed in an exhaust passage of the internal combustion engine, and a compressor disposed in an intake passage of the internal combustion engine; 
 a bypass passage that branches off from the exhaust passage upstream of the turbine and merges with the exhaust passage downstream of the turbine; 
 a wastegate valve that is disposed at an exit of the bypass passage and is configured to change a channel cross-sectional area of gas at the exit of the bypass passage, the wastegate valve including a valve body portion supported on a single side, the wastegate valve being configured to change an opening degree by swinging the valve body portion, the wastegate valve being configured to change a flow direction of bypass gas in accordance with the change in opening degree, and the bypass gas being gas flowing out from the exit of the bypass passage; 
 a turbo bypass valve that is disposed between a branch portion of the exhaust passage where the bypass passage branches off from the exhaust passage, and a merging portion of the exhaust passage where the bypass passage merges with the exhaust passage, and is configured to change the channel cross-sectional area of gas passing through the turbine; 
 a three-way catalyst that is disposed immediately downstream of the merging portion of the exhaust passage where the bypass passage merges with the exhaust passage, the three-way catalyst being disposed in a position in which an area of inflow of the bypass gas on an upstream side end surface of the three-way catalyst is changed in accordance with the change in the flow direction of the bypass gas; and 
 an electronic control unit configured to
 execute fuel cut control that stops fuel injection to the internal combustion engine, at a time of a decelerating operation, 
 control the turbo bypass valve to be in a fully closed state and control the opening degree of the wastegate valve to a first predetermined opening degree during execution of the fuel cut control, and 
 maintain the turbo bypass valve in the fully closed state and control the opening degree of the wastegate valve to a second predetermined opening degree different from the first predetermined opening degree when a boost request is not made for the internal combustion engine at an end of the fuel cut control, 
 wherein the wastegate valve and the three-way catalyst are configured such that an area of inflow of the bypass gas on the upstream side end surface of the three-way catalyst when the opening degree of the wastegate valve is controlled to the first predetermined opening degree is in a different position from the area of inflow of the bypass gas on the upstream side end surface of the three-way catalyst when the opening degree of the wastegate valve is controlled to the second predetermined opening degree. 
 
 
     
     
       2. The exhaust system according to  claim 1 , wherein:
 the wastegate valve and the three-way catalyst are configured such that the bypass gas flows into a first predetermined area on the upstream side end surface of the three-way catalyst when the opening degree of the wastegate valve is controlled to the first predetermined opening degree, the first predetermined area being an area on an outer side from a second predetermined area that is an area including a center portion on the upstream side end surface of the three-way catalyst; and 
 the wastegate valve and the three-way catalyst are configured such that the bypass gas flows into the second predetermined area on the upstream side end surface of the three-way catalyst when the opening degree of the wastegate valve is controlled to the second predetermined opening degree larger than the first predetermined opening degree. 
 
     
     
       3. The exhaust system according to  claim 1 , wherein the electronic control unit is configured to control the turbo bypass valve to be in a fully opened state and control the opening degree of the wastegate valve to an opening degree corresponding to a requested boost pressure when a boost request is made for the internal combustion engine at the end of the fuel cut control. 
     
     
       4. The exhaust system according to  claim 1 , wherein:
 the electronic control unit is configured to execute an enrichment process that decreases an air-fuel ratio of gas flowing into the three-way catalyst to a low rich air-fuel ratio lower than a stoichiometric air-fuel ratio, at the end of the fuel cut control; and 
 the electronic control unit is configured to determine a target air-fuel ratio of gas in the enrichment process or a period of execution of the enrichment process in accordance with an amount of oxygen retained in the three-way catalyst at the end of execution of the fuel cut control.