Evaporative fuel treatment apparatus for internal combustion engine

Abstract

An evaporative fuel treatment apparatus for an internal combustion engine includes: a communication portion that communicates a plurality of branch passages with one another at positions downstream of the plurality of throttle valves; a purge passage that introduces purge gas, containing evaporative fuel, to the communication portion; an air supply passage that flows dilution air, which is used to dilute the evaporative fuel, into the purge passage; a first flow rate changing portion that is provided in the air supply passage and that is able to change the inflow of the dilution air; and a control unit that controls the first flow rate changing portion.

1 . An evaporative fuel treatment apparatus for an internal combustion engine, comprising:
 a plurality of branch passages that respectively communicate with a plurality of cylinders;   a plurality of throttle valves that are respectively provided in the plurality of branch passages, wherein each of the plurality of throttle valves is able to change the amount of air taken into a corresponding one of the plurality of cylinders;   a balancing passage that communicates the plurality of branch passages with one another at positions downstream of the plurality of throttle valves;   a communication portion that communicates the plurality of branch passages with one another at positions downstream of the plurality of throttle valves;   a purge passage that introduces purge gas, containing evaporative fuel generated in a fuel tank, to the communication portion;   an air supply passage that flows dilution air, which is used to dilute the evaporative fuel, into the purge passage;   a first flow rate changing portion that is provided in the air supply passage and that is able to change the inflow of the dilution air; and   a control unit that controls the first flow rate changing portion such that the inflow of the dilution air is changed on the basis of a comparison between the concentration of the evaporative fuel and a predetermined concentration determined on the basis of an operating state of the internal combustion engine.   
     
     
         2 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 1 , wherein the flow passage area of the communication portion is smaller than the flow passage area of the balancing passage. 
     
     
         3 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 1 , wherein the dilution air is air taken from an intake system upstream of the plurality of throttle valves. 
     
     
         4 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 1 , further comprising a second flow rate changing portion that changes the flow rate of the purge gas introduced from the fuel tank to the purge passage, wherein the control unit controls the second flow rate changing portion such that the flow rate of the purge gas introduced to the purge passage reduces, when an actual flow rate of dilution air, which is changeable by the first flow rate changing portion, is smaller than a predetermined flow rate of the dilution air by which the concentration of the evaporative fuel is reduced below the predetermined concentration. 
     
     
         5 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 1 , further comprising a concentration determination portion that determines the concentration of the evaporative fuel, wherein
 the control unit controls the first flow rate changing portion such that the inflow of the dilution air increases, when the determined concentration of the evaporative fuel is higher than the predetermined concentration, and controls the first flow rate changing portion such that the inflow of the dilution air reduces, when the determined concentration of the evaporative fuel is lower than the predetermined concentration.   
     
     
         6 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 1 , further comprising an intake air flow rate detector that is provided in the intake system upstream of a branch position at which the branch passages branch off and that detects the flow rate of intake air, wherein
 the air supply passage takes air out of the intake system downstream of the intake air flow rate detector and upstream of the branch position and flows the taken out air into the purge passage.   
     
     
         7 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 6 , further comprising a surge tank that is arranged downstream of the intake air flow rate detector and upstream of the branch position and that forms part of the intake system, wherein
 the air supply passage takes air out of the surge tank and flows the taken out air into the purge passage.   
     
     
         8 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 1 , further comprising a mixing promoting portion that is provided between the communication portion and a connecting position at which the air supply passage is connected to the purge passage, and that promotes mixing of air introduced through the air supply passage with purge gas introduced to the purge passage. 
     
     
         9 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 8 , wherein the purge passage meanders between the communication portion and the connecting position to form the mixing promoting portion. 
     
     
         10 . An evaporative fuel treatment apparatus for a multi-cylinder internal combustion engine that includes a pair of first and second banks respectively having a plurality of cylinders, comprising:
 a plurality of branch passages that respectively communicate with the plurality of cylinders in each bank;   a plurality of throttle valves that are respectively provided in the plurality of branch passages in each bank, wherein each of the plurality of throttle valves is able to change the amount of air taken into a corresponding one of the plurality of cylinders;   a balancing passage that communicates the plurality of branch passages with one another at positions downstream of the plurality of throttle valves in each bank;   a communication portion that communicates the plurality of branch passages with one another at positions downstream of the plurality of throttle valves in the first bank;   a purge passage that introduces purge gas, containing evaporative fuel generated in a fuel tank, to the communication portion in the first bank;   an air supply passage that flows dilution air, which is used to dilute the evaporative fuel, into the purge passage in the first bank;   a first flow rate changing portion that is provided in the air supply passage in the first bank and that is able to change the inflow of the dilution air; and   a control unit that controls the opening degrees of the plurality of throttle valves in the second bank so that the amount of air taken into the second bank reduces by a differential flow rate, when an actual flow rate of dilution air that is changeable by the first flow rate changing portion is smaller than a predetermine flow rate of the dilution air used to reduce the concentration of the evaporative fuel below a predetermined concentration determined on the basis of an operating state of the internal combustion engine, wherein the differential flow rate is a difference between the predetermined flow rate and the actual flow rate.   
     
     
         11 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 10 , wherein the flow passage area of the communication portion is smaller than the flow passage area of the balancing passage. 
     
     
         12 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 10 , wherein the dilution air is air taken from an intake system upstream of the plurality of throttle valves. 
     
     
         13 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 10 , wherein the control unit controls the opening degrees of the plurality of throttle valves in the second bank so that the amount of air taken into the second bank is determined so that combustion in the cylinders of the second bank is occurable and/or is larger than a lower limit intake air amount determined on the basis of an air-fuel ratio required in the second bank. 
     
     
         14 . An evaporative fuel treatment apparatus for a multi-cylinder internal combustion engine that includes a pair of first and second banks respectively having a plurality of cylinders, comprising:
 a plurality of branch passages that respectively communicate with the plurality of cylinders in each bank;   a plurality of throttle valves that are respectively provided in the plurality of branch passages in each bank, wherein each of the plurality of throttle valves is able to change the amount of air taken into a corresponding one of the plurality of cylinders;   a balancing passage that communicates the plurality of branch passages with one another at positions downstream of the plurality of throttle valves in each bank;   a communication portion that communicates the plurality of branch passages with one another at positions downstream of the plurality of throttle valves in each bank;   a purge passage that introduces purge gas, containing evaporative fuel generated in a fuel tank, to the communication portion in the first bank;   a first air supply passage that flows dilution air, which is used to dilute the evaporative fuel, from an intake system upstream of the plurality of throttle valves into the purge passage in the first bank;   a second air supply passage that flows upstream air, in the second bank, from an intake system upstream of the plurality of throttle valves into the communication portion of the second bank;   a first flow rate changing portion that is provided in the first air supply passage in the first bank and that is able to change the inflow of the dilution air;   a second flow rate changing portion that is provided in the second air supply passage in the second bank and that is able to change the inflow of the upstream air; and   a control unit that controls the first flow rate changing portion such that the inflow of the dilution air is changed on the basis of a comparison between the concentration of the evaporative fuel and a predetermined concentration determined on the basis of an operating state of the internal combustion engine, and that controls the second flow rate changing portion such that the inflow of the dilution air is equalized to the inflow of the upstream air.   
     
     
         15 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 14 , wherein the flow passage area of the communication portion is smaller than the flow passage area of the balancing passage. 
     
     
         16 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 1 , further comprising:
 a second flow rate changing portion that changes the flow rate of the purge gas introduced from the fuel tank to the purge passage;   a pressure measurement portion that measures a purge pressure at a position downstream of the second flow rate changing portion; and   an estimation unit that estimates the purge pressure on the basis of an operating state of the internal combustion engine, wherein   the control unit controls the first flow rate changing portion such that the inflow of the dilution air is maintained at a constant value, when the pressure measurement portion fails.   
     
     
         17 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 10 , further comprising:
 a second flow rate changing portion that changes the flow rate of the purge gas introduced from the fuel tank to the purge passage;   a pressure measurement portion that measures a purge pressure at a position downstream of the second flow rate changing portion; and   an estimation unit that estimates the purge pressure on the basis of an operating state of the internal combustion engine, wherein   the control unit controls the first flow rate changing portion such that the inflow of the dilution air is maintained at a constant value, when the pressure measurement portion fails.   
     
     
         18 . The evaporative fuel treatment apparatus for an internal combustion engine according to  claim 14 , further comprising:
 a second flow rate changing portion that changes the flow rate of the purge gas introduced from the fuel tank to the purge passage;   a pressure measurement portion that measures a purge pressure at a position downstream of the second flow rate changing portion; and   an estimation unit that estimates the purge pressure on the basis of an operating state of the internal combustion engine, wherein   the control unit controls the first flow rate changing portion such that the inflow of the dilution air is maintained at a constant value, when the pressure measurement portion fails.