Engine exhaust gas temperature control system

Abstract

An engine exhaust gas temperature control system comprises a combustion chamber, a fuel supplying device, a secondary air supplying device and a control unit. The fuel supplying device is configured and arranged to supply fuel into an intake passage. The secondary air supplying device is configured and arranged to selectively supply secondary air to an exhaust passage. The control unit is configured to execute a secondary air combustion operation in which a valve overlapping period during which an intake valve and an exhaust valve are both open is set and the fuel supplying device is controlled to inject the fuel into the intake passage so that a portion of the fuel that blows by a combustion chamber and into the exhaust passage during the valve overlapping period is combusted by the secondary air supplied by the secondary air supplying device.

1 . An engine exhaust gas temperature control system comprising: 
 a combustion chamber fluidly coupled to an intake passage and an exhaust passage with an intake valve being disposed between the intake passage and the combustion chamber and an exhaust valve being disposed between the exhaust passage and the combustion chamber;    a fuel supplying device configured and arranged to supply fuel into the intake passage;    a secondary air supplying device configured and arranged to selectively supply secondary air to the exhaust passage; and    a control unit configured to execute a secondary air combustion operation in which a valve overlapping period during which the intake valve and the exhaust valve are both open is set and the fuel supplying device is controlled to inject the fuel into the intake passage so that a portion of the fuel that blows by the combustion chamber and into the exhaust passage during the valve overlapping period is combusted by the secondary air supplied by the secondary air supplying device.    
   
   
       2 . The engine exhaust gas temperature control system recited in  claim 1 , further comprising 
 a variable valve operating device operatively coupled to the control unit, and configured and arranged to change the valve overlapping period by changing a lift characteristic of at least one of the intake valve and the exhaust valve,    the control unit being further configured to control the variable valve operating device so that the valve overlapping period during operation of the secondary air supplying device is longer than the valve overlapping period when the secondary air supplying device is not operating.    
   
   
       3 . The engine exhaust gas temperature control system recited in  claim 2 , wherein 
 the control unit is configured to control the variable valve operating device so that a lift amount of the intake valve during operation of the secondary air supplying device is smaller than the lift amount of the intake valve when the secondary air supplying device is not operating.    
   
   
       4 . The engine exhaust gas temperature control system recited in  claim 1 , further comprising 
 an exhaust gas cleaning catalytic converter provided in the exhaust passage,    the control unit being further configured to operate the secondary air supplying device and to execute the secondary air combustion operation upon a temperature increase condition is satisfied.    
   
   
       5 . The engine exhaust gas temperature control system recited in  claim 1 , wherein 
 the fuel supplying device includes a fuel injection valve that is configured and arranged to inject fuel into an intake port of the intake passage,    the control unit is further configured to control the fuel injection valve to inject the fuel into the intake port during at least part of the valve overlapping period.    
   
   
       6 . The engine exhaust gas temperature control system recited in  claim 5 , wherein 
 the control unit is further configured to control the fuel injection valve to inject the fuel into the intake port from a timing before the valve overlapping period starts to a timing after the valve overlapping period ends.    
   
   
       7 . The engine exhaust gas temperature control system recited in  claim 5 , wherein 
 the control unit is further configured to prohibit the fuel injection valve from injecting fuel during the valve overlapping period until a prescribed amount of time elapses after an operation of the secondary air supplying device is started.    
   
   
       8 . The engine exhaust gas temperature control system recited in  claim 5 , wherein 
 the control unit is further configured to prohibit the secondary air combustion operation until a prescribed amount of time elapses after an operation of the secondary air supplying device is started.    
   
   
       9 . The engine exhaust gas temperature control system recited in  claim 5 , further comprising 
 a variable valve operating device operatively coupled to the control unit, and configured and arranged to change the valve overlapping period by changing a lift characteristic of at least one of the intake valve and the exhaust valve,    the control unit being further configured to control the variable valve operating device so that the valve overlapping period during operation of the secondary air supplying device is longer than the valve overlapping period when the secondary air supplying device is not operating.    
   
   
       10 . The engine exhaust gas temperature control system recited in  claim 9 , wherein 
 the control unit is configured to control the variable valve operating device so that a lift amount of the intake valve during operation of the secondary air supplying device is smaller than the lift amount of the intake valve when the secondary air supplying device is not operating.    
   
   
       11 . The engine exhaust gas temperature control system recited in  claim 5 , further comprising 
 an exhaust gas cleaning catalytic converter provided in the exhaust passage,    the control unit being further configured to operate the secondary air supplying device and to execute the secondary air combustion operation upon a temperature increase condition is satisfied.    
   
   
       12 . The engine exhaust gas temperature control system recited in  claim 11 , wherein 
 the control unit is further configured to prohibit the secondary air combustion operation until a prescribed amount of time elapses after an operation of the secondary air supplying device is started.    
   
   
       13 . A method of controlling an engine exhaust gas temperature comprising: 
 providing a combustion chamber fluidly coupled to an intake passage and an exhaust passage with an intake valve being disposed between the intake passage and the combustion chamber and an exhaust valve being disposed between the exhaust passage and the combustion chamber;    supplying secondary air to the exhaust passage;    setting an valve overlapping period during which the intake valve and the exhaust valve are both open; and    supplying fuel into the intake passage so that a portion of the fuel that blows by the combustion chamber and into the exhaust passage during the valve overlapping period is combusted by the secondary air in the exhaust passage.    
   
   
       14 . The method as recited in  claim 13 , wherein 
 the setting of the valve overlapping period is performed by controlling a lift characteristic of at least one of the intake valve and the exhaust valve.    
   
   
       15 . The method as recited in  claim 13 , wherein 
 the supplying of the fuel into the intake passage is performed by supplying the fuel into an intake port of the intake passage during the valve overlapping period.    
   
   
       16 . An engine exhaust gas temperature control system comprising: 
 means for providing a combustion chamber fluidly coupled to an intake passage and an exhaust passage with an intake valve being disposed between the intake passage and the combustion chamber and an exhaust valve being disposed between the exhaust passage and the combustion chamber;    secondary air supplying means for supplying secondary air to the exhaust passage;    valve overlapping period setting means for setting an valve overlapping period during which the intake valve and the exhaust valve are both open; and    fuel supplying means for supplying fuel into the intake passage so that a portion of the fuel that blows by the combustion chamber and into the exhaust passage during the valve overlapping period is combusted by the secondary air in the exhaust passage.    
   
   
       17 . The engine exhaust gas temperature control system recited in  claim 16 , wherein 
 the valve overlapping period setting means further includes a function for controlling a lift characteristic of at least one of the intake valve and the exhaust valve for setting the valve overlapping period.    
   
   
       18 . The engine exhaust gas temperature control system recited in  claim 16 , wherein 
 the fuel supplying means further includes a function for supplying the fuel into an intake port of the intake passage during the valve overlapping period.