Control of autoignition timing in a HCCI engine

Abstract

Method and system embody a valve timing strategy to control the autoignition timing of a four stroke internal combustion engine ( 10 ) operated in an HCCI mode at different engine operating conditions such as different engine speed and torque. A particular valve timing strategy varies lift timing of the intake valve ( 20 ) relative to the exhaust valve ( 28 ), or vice versa, and relative to top dead center in response to a change in engine torque, for example, to vary amount of trapped residual burned gas in the combustion chamber ( 12 ) flowing to an intake or exhaust port ( 16,18 ) and back to the combustion chamber during which the residual gas is cooled. Control of the flow of residual gas between the combustion chamber and intake or exhaust port and thus its temperature by the valve timing strategy, in turn, is used to control the temperature of the fresh air/residual gas/fuel mixture in the combustion chamber ( 12 ) and thus autoignition timing in response to a change in engine torque.

1 - 19 . (canceled)  
   
   
       20 . A method for operating a 4-stroke, auto-ignited, internal combustion engine having a cylinder with an intake valve and an exhaust valve coupled thereto, comprising: 
 determining an operator demanded engine torque;    adjusting an opening time of the intake valve; and    adjusting an air-fuel ratio supplied to the cylinder wherein the intake valve opening time and said air-fuel ratio are adjusted in response to said operator demanded engine torque.    
   
   
       21 . The method of  claim 20  wherein an exhaust valve closing time is substantially fixed before top dead center and said intake valve opening time is varied after top dead center over successive engine cycles to provide successive intake events that change autoignition timing.  
   
   
       22 . The method of  claim 20  wherein said air-fuel ratio is adjusted over successive engine cycles to provide successive intake events that change autoignition timing.  
   
   
       23 . The method of  claim 20  wherein said intake valve opening time and said air-fuel ratio are adjusted to substantially provide said operator demanded engine torque.  
   
   
       24 . The method of  claim 20 , further comprising: 
 adjusting an exhaust valve closing time such that the intake valve and exhaust valve are open simultaneously wherein said exhaust valve closing time adjustment causes said air-fuel ratio adjustment.    
   
   
       25 . A compression-ignited internal combustion engine, comprising: 
 a cylinder;    an intake valve coupled to said cylinder;    an exhaust valve coupled to said cylinder;    an accelerator pedal depression sensor; and    an electronic control unit electronically coupled to said intake valve, said exhaust valve, and said pedal sensor, said electronic control unit determining an operator demanded engine torque based on a signal from said pedal sensor, said electronic control unit adjusting both an opening time of said intake valve and a closing time of said exhaust valve to cause the engine to provide substantially said operator demanded engine torque.    
   
   
       26 . The engine of  claim 25  wherein said exhaust valve dosing time adjustment affects an air-fuel ratio in said cylinder.  
   
   
       27 . The engine of  claim 26  wherein said intake valve closing time adjustment affects an amount of backflow through said intake valve from said cylinder to an engine intake thereby affecting temperature of the gases in said cylinder and said autoignition timing.  
   
   
       28 . The engine of  claim 25  wherein said adjustments are made over successive engine cycles.  
   
   
       29 . The engine of  claim 25  wherein said electronic control unit commands said intake valve to open an additional time said additional time occurring prior to top dead center and said adjusted valve opening occurring after top dead center.  
   
   
       30 . The engine of  claim 25  wherein said electronic control unit commands said exhaust valve to open an additional time said additional time occurring after top dead center and said exhaust valve closing occurring prior to top dead center.  
   
   
       31 . A computer readable storage medium having stored data representing instructions executable by a computer for controlling an internal combustion engine having a cylinder with an intake valve and an exhaust valve coupled thereto comprising: 
 instructions to determine an operator demanded engine torque;    instructions to adjust an opening time of the intake valve; and    instructions to adjust a closing time of the exhaust valve wherein said intake valve opening time and said exhaust closing time are adjusted in response to said operator demanded engine torque.    
   
   
       32 . The media of  claim 31 , further comprising: instructions to determine a desired autoignition time to provide said operator demanded engine torque wherein said opening time of the intake valve affects said autoignition time.  
   
   
       33 . The media of  claim 31 , further comprising: instructions to cause said adjustments in intake valve opening time and exhaust valve closing time to be made over successive engine cycles.