Four-stroke gasoline engine with direct injection and method for valve control

Abstract

The invention relates to a method for actuating intake valves and exhaust valves of a four-stroke direct-injection gasoline engine. At low torque, a parallel retardation of the intake valves and exhaust valves is carried out, so that, at the commencement of the intake stroke, the exhaust valve is still open and the intake valve is still closed after top dead center (TDC) of the piston. High internal exhaust gas recirculation (EGR) occurs, irrespective of the pressure in the intake manifold. The resulting internal EGR is sufficient to displace the 50% MFB timing to its optimal position after TDC and to reduce nitrogen oxide emissions.

I claim:  
     
         1 . A method for controlling at least one intake valve and at least one exhaust valve of a four-stroke direct-injection gasoline engine under low torque operation, comprising: retarding an opening of the intake valve so that the intake valve opens after top dead center (TDC) of the piston.  
     
     
         2 . The method of  claim 1  wherein the intake valve retardation is adjusted so that the 50% fuel mass fraction burned time occurs at about 9 crank angle degrees after TDC of expansion.  
     
     
         3 . The method of  claim 1  wherein the intake valve opening occurs after a closing time of the exhaust valve.  
     
     
         4 . The method of  claim 1  further comprising: adjusting a closing time of the exhaust valve to occur at least 45 crank angle degrees after TDC of intake.  
     
     
         5 . The method of  claim 1 , further comprising: adjusting said opening time of the intake valve to occur at least 45 crank angle degrees after TDC.  
     
     
         6 . The method of  claim 1  wherein the intake valve and the exhaust valve are actuated by a common camshaft of adjustable phase.  
     
     
         7 . The method of  claim 1 , wherein the intake valve is actuated by an intake camshaft of adjustable phase and the exhaust valve is actuated by an exhaust camshaft of adjustable phase.  
     
     
         8 . A four-stroke, direct-injection gasoline engine having at least one intake valve, at least one exhaust valve, and a camshaft, comprising: 
 an engine controller electrically coupled to the engine and the camshaft, said engine controller causes a phase displacement of the camshaft to cause an opening of the intake valve so that the intake valve opens after top dead center (TDC) of the piston.    
     
     
         9 . The engine of  claim 8  wherein the engine controller causes the exhaust valve closing time to occur at least 45 degrees after TDC.  
     
     
         10 . The engine of  claim 8  wherein the engine controller causes the intake valve opening time to occur at least 45 degrees after TDC.  
     
     
         11 . The engine of  claim 8  wherein the camshaft actuates the intake valve, comprising: an exhaust camshaft actuating the exhaust valve.  
     
     
         12 . The engine of  claim 8 , wherein the camshaft is arranged overhead.