Exhaust Gas Purification System for a V Type 8-Cylinder Internal Combustion Engine

Abstract

A technique that suppresses adhesion of fuel added from fuel addition valves to exhaust passages and suppresses fuel from slipping through exhaust gas purification devices is provided. Timing of the addition of fuel is switched into a period in which instantaneous exhaust gas flow rates in the exhaust passages are different, in accordance with engine operating condition. As a result, when operating condition has a high possibility of fuel adhering to the exhaust pipes, fuel is added when the instantaneous exhaust gas flow rates in the exhaust pipes are high, so that fuel can be easily carried to the vicinity of the exhaust gas purification devices. When the operating condition has a high possibility of fuel slipping through the exhaust gas purification devices, fuel is added when the instantaneous exhaust gas flow rates in the exhaust pipes are low, so that the fuel can not be easily entrained in the exhaust gas to slow movement of fuel.

1 . An exhaust gas purification system for a V-type 8-cylinder internal combustion engine, comprising:
 exhaust passages that are provided for individual banks, respectively, in the V-type 8-cylinder internal combustion engine and extend collectively from individual cylinders in the individual banks, respectively, so as to pass therein an exhaust gas from said internal combustion engine;   exhaust gas purification devices that are arranged on said exhaust passages, respectively, and are each constructed to include a catalyst having an oxidation function; and   fuel addition valves that are disposed on said exhaust passages at an upstream side of said exhaust gas purification devices, respectively, for adding fuel to the exhaust gas passing through said exhaust passages when the performance of said exhaust gas purification devices is to be recovered;   wherein timing of the addition of fuel at which fuel is added from said fuel addition valves is switched over into a period in which instantaneous exhaust gas flow rates in said exhaust passages are different from each other, in accordance with an engine operating condition.   
   
   
       2 . The exhaust gas purification system for a V-type 8-cylinder internal combustion engine as set forth in  claim 1 , wherein said timing of the addition of fuel is switched over into a period in which the instantaneous exhaust gas flow rates in said exhaust passages become smaller in accordance with an increasing amount of accumulation of a flow rate of exhaust gas discharged in a predetermined cycle period. 
   
   
       3 . The exhaust gas purification system for a V-type 8-cylinder internal combustion engine as set forth in  claim 1 , wherein said timing of the addition of fuel is switched over into a period in which the instantaneous exhaust gas flow rates in said exhaust passages become smaller, in accordance with the higher temperature of the exhaust gas. 
   
   
       4 . The exhaust gas purification system for a V-type 8-cylinder internal combustion engine as set forth in  claim 1 , wherein:
 said V-type 8-cylinder internal combustion engine is a V-type 8-cylinder internal combustion engine in which combustion can be continuously performed in predetermined two cylinders of the same bank in a crank angle interval of 90 degrees, and in which no combustion can be performed in any of the cylinders of the same bank in a crank angle interval of 180 degrees; and   in accordance with the engine operating condition, said timing of the addition of fuel is switched over into one of the following periods, i.e., a period in which exhaust valves in two cylinders of the same bank in case where combustion is performed continuously in the crank angle interval of 90 degrees are both in their open state, a latter half period in which an exhaust valve in a predetermined one cylinder in case where no combustion is performed in a crank angle interval of 90 degrees before and after combustion is performed in the predetermined one cylinder of the same bank is in its open state, a former half period in which an exhaust valve in a predetermined one cylinder in case where no combustion is performed in a crank angle interval of 90 degrees before and after combustion is performed in the predetermined one cylinder of the same bank is in its open state, and a period in which exhaust valves in all the cylinders of the same bank in case where no combustion is performed in any cylinder in a crank angle interval of 180 degrees are in their closed state.   
   
   
       5 . The exhaust gas purification system for a V-type 8-cylinder internal combustion engine as set forth in  claim 2 , wherein:
 said V-type 8-cylinder internal combustion engine is a V-type 8-cylinder internal combustion engine in which combustion can be continuously performed in predetermined two cylinders of the same bank in a crank angle interval of 90 degrees, and in which no combustion can be performed in any of the cylinders of the same bank in a crank angle interval of 180 degrees;   when said amount of accumulation is equal to or smaller than a first predetermined amount of accumulation, said timing of the addition of fuel is switched to a period in which exhaust valves in two cylinders of the same bank in case where combustion is continuously performed in a crank angle interval of 90 degrees are both in their open state;   when said amount of accumulation is equal to or more than a second predetermined amount of accumulation which is more than said first predetermined amount of accumulation, said timing of the addition of fuel is switched to a period in which exhaust valves in all the cylinders of the same bank in case where no combustion is performed in any cylinder in a crank angle interval of 180 degrees are in their closed state; and   when said amount of accumulation is more than said first predetermined amount of accumulation and is less than said second predetermined amount of accumulation, said timing of the addition of fuel is switched to a period in which an exhaust valve in a predetermined one cylinder in case where no combustion is performed in a crank angle interval of 90 degrees before and after combustion is performed in the predetermined one cylinder of the same bank is in its open state.   
   
   
       6 . The exhaust gas purification system for a V-type 8-cylinder internal combustion engine as set forth in  claim 5 , wherein:
 when said amount of accumulation is more than the first predetermined amount of accumulation and is equal to or less than a third predetermined amount of accumulation which is between the first predetermined amount of accumulation and the second predetermined amount of accumulation, said timing of the addition of fuel is switched to a latter half period in which the exhaust valve in said predetermined one cylinder is in its open state;   when said amount of accumulation is more than the third predetermined amount of accumulation which is between the first predetermined amount of accumulation and the second predetermined amount of accumulation, and is less than the second predetermined amount of accumulation, said timing of the addition of fuel is switched to a former half period in which the exhaust valve in said predetermined one cylinder is in its open state.   
   
   
       7 . The exhaust gas purification system for a V-type 8-cylinder internal combustion engine as set forth in  claim 2 , wherein said timing of the addition of fuel is switched over into a period in which the instantaneous exhaust gas flow rates in said exhaust passages become smaller, in accordance with the higher temperature of the exhaust gas. 
   
   
       8 . The exhaust gas purification system for a V-type 8-cylinder internal combustion engine as set forth in  claim 2 , wherein:
 said V-type 8-cylinder internal combustion engine is a V-type 8-cylinder internal combustion engine in which combustion can be continuously performed in predetermined two cylinders of the same bank in a crank angle interval of 90 degrees, and in which no combustion can be performed in any of the cylinders of the same bank in a crank angle interval of 180 degrees; and   in accordance with the engine operating condition, said timing of the addition of fuel is switched over into one of the following periods, i.e., a period in which exhaust valves in two cylinders of the same bank in case where combustion is performed continuously in the crank angle interval of 90 degrees are both in their open state, a latter half period in which an exhaust valve in a predetermined one cylinder in case where no combustion is performed in a crank angle interval of 90 degrees before and after combustion is performed in the predetermined one cylinder of the same bank is in its open state, a former half period in which an exhaust valve in a predetermined one cylinder in case where no combustion is performed in a crank angle interval of 90 degrees before and after combustion is performed in the predetermined one cylinder of the same bank is in its open state, and a period in which exhaust valves in all the cylinders of the same bank in case where no combustion is performed in any cylinder in a crank angle interval of 180 degrees are in their closed state.   
   
   
       9 . The exhaust gas purification system for a V-type 8-cylinder internal combustion engine as set forth in  claim 3 , wherein:
 said V-type 8-cylinder internal combustion engine is a V-type 8-cylinder internal combustion engine in which combustion can be continuously performed in predetermined two cylinders of the same bank in a crank angle interval of 90 degrees, and in which no combustion can be performed in any of the cylinders of the same bank in a crank angle interval of 180 degrees; and   in accordance with the engine operating condition, said timing of the addition of fuel is switched over into one of the following periods, i.e., a period in which exhaust valves in two cylinders of the same bank in case where combustion is performed continuously in the crank angle interval of 90 degrees are both in their open state, a latter half period in which an exhaust valve in a predetermined one cylinder in case where no combustion is performed in a crank angle interval of 90 degrees before and after combustion is performed in the predetermined one cylinder of the same bank is in its open state, a former half period in which an exhaust valve in a predetermined one cylinder in case where no combustion is performed in a crank angle interval of 90 degrees before and after combustion is performed in the predetermined one cylinder of the same bank is in its open state, and a period in which exhaust valves in all the cylinders of the same bank in case where no combustion is performed in any cylinder in a crank angle interval of 180 degrees are in their closed state.   
   
   
       10 . The exhaust gas purification system for a V-type 8-cylinder internal combustion engine as set forth in  claim 7 , wherein:
 said V-type 8-cylinder internal combustion engine is a V-type 8-cylinder internal combustion engine in which combustion can be continuously performed in predetermined two cylinders of the same bank in a crank angle interval of 90 degrees, and in which no combustion can be performed in any of the cylinders of the same bank in a crank angle interval of 180 degrees; and   in accordance with the engine operating condition, said timing of the addition of fuel is switched over into one of the following periods, i.e., a period in which exhaust valves in two cylinders of the same bank in case where combustion is performed continuously in the crank angle interval of 90 degrees are both in their open state, a latter half period in which an exhaust valve in a predetermined one cylinder in case where no combustion is performed in a crank angle interval of 90 degrees before and after combustion is performed in the predetermined one cylinder of the same bank is in its open state, a former half period in which an exhaust valve in a predetermined one cylinder in case where no combustion is performed in a crank angle interval of 90 degrees before and after combustion is performed in the predetermined one cylinder of the same bank is in its open state, and a period in which exhaust valves in all the cylinders of the same bank in case where no combustion is performed in any cylinder in a crank angle interval of 180 degrees are in their closed state.