Engine including variable valve lift mechanism

Abstract

An engine assembly may include an engine structure, an engine valve, a valve lift mechanism, and first and second camshafts. The engine structure may define a combustion chamber and a port in communication with the combustion chamber. The engine valve may be supported by the engine structure and displaceable between an open position where the port is in communication with the combustion chamber and a closed position to isolate the port from communication with the combustion chamber. The valve lift mechanism may be engaged with the engine valve. The first camshaft may be rotationally supported by the engine structure and may include a first cam lobe engaged with the valve lift mechanism. The second camshaft may be rotationally supported by the engine structure and may include a second cam lobe engaged with the valve lift mechanism.

What is claimed is: 
     
         1 . An engine assembly comprising:
 an engine structure defining a combustion chamber and a port in communication with the combustion chamber;   an engine valve supported by the engine structure and displaceable between an open position where the port is in communication with the combustion chamber and a closed position to isolate the port from communication with the combustion chamber;   a valve lift mechanism engaged with the engine valve;   a first camshaft rotationally supported by the engine structure and including a first cam lobe engaged with the valve lift mechanism; and   a second camshaft rotationally supported by the engine structure and including a second cam lobe engaged with the valve lift mechanism.   
     
     
         2 . The engine assembly of  claim 1 , further comprising a first cam phaser coupled to the first camshaft and operable to rotate the first camshaft between first and second positions relative to the second camshaft to vary a lift profile of the engine valve. 
     
     
         3 . The engine assembly of  claim 2 , wherein a first peak of the first cam lobe is engaged with the valve lift mechanism when a second peak of the second cam lobe is engaged with valve lift mechanism when the first camshaft is in the first position. 
     
     
         4 . The engine assembly of  claim 3 , wherein the first peak of the first cam lobe is rotationally offset from the valve lift mechanism when the second peak of the second cam lobe is engaged with valve lift mechanism when the first camshaft is in the second position. 
     
     
         5 . The engine assembly of  claim 2 , further comprising a second cam phaser coupled to the second camshaft and operable to rotate the second camshaft relative to the first camshaft. 
     
     
         6 . The engine assembly of  claim 5 , wherein the lift profile defines a maximum valve lift height of the engine valve when the first cam lobe is in a fully retarded position and the second cam lobe is in a fully advanced position. 
     
     
         7 . The engine assembly of  claim 6 , wherein the lift profile defines a maximum retard condition for opening of the engine valve when the first cam lobe is in a fully retarded position and the second cam lobe is in a fully retarded position. 
     
     
         8 . The engine assembly of  claim 6 , wherein the lift profile defines a maximum advanced condition for opening of the engine valve when the first cam lobe is in a fully advanced position and the second cam lobe is in a fully advanced position. 
     
     
         9 . The engine assembly of  claim 6 , wherein the lift profile defines a maximum opening duration of the engine valve when the first cam lobe is in a fully advanced position and the second cam lobe is in a fully retarded position. 
     
     
         10 . The engine assembly of  claim 2 , wherein the valve lift mechanism includes a pivot arm defining a first end engaged with the first cam lobe, a second end engaged with the second cam lobe and a pivot located between the first and second ends, the valve lift profile being varied by the first and second cam lobes adjusting a rotational orientation of the valve lift mechanism about the pivot. 
     
     
         11 . A method comprising:
 displacing an engine valve from a closed position to an open position at a first valve lift profile to provide communication between an engine port and an engine combustion chamber, the displacing including a first cam lobe on a first camshaft and a second cam lobe on a second camshaft engaging a valve lift mechanism engaged with the engine valve;   rotating the first camshaft relative to the second camshaft; and   displacing the engine valve from the closed position to the open position at a second valve lift profile different than the first valve lift profile after the rotating via engagement between the first and second cam lobes and the valve lift mechanism.   
     
     
         12 . The method of  claim 11 , wherein the rotating includes actuating a cam phaser coupled to the first camshaft. 
     
     
         13 . The method of  claim 12 , wherein the first valve lift profile includes a peak of the first cam lobe being engaged with the valve lift mechanism when a peak of the second cam lobe is engaged with the valve lift mechanism. 
     
     
         14 . The method of  claim 13 , wherein the second valve lift profile includes the peak of the first cam lobe being rotationally offset from the valve lift mechanism when the peak of the second cam lobe is engaged with the valve lift mechanism. 
     
     
         15 . The method of  claim 12 , further comprising rotating the second camshaft relative to the first camshaft via a second cam phaser coupled to the second camshaft. 
     
     
         16 . The method of  claim 15 , wherein the engine valve is displaced to a maximum valve lift height when the first cam lobe is in a fully retarded position and the second cam lobe is in a fully advanced position. 
     
     
         17 . The method of  claim 16 , wherein a maximum retard condition for displacement of the engine valve is defined when the first cam lobe is in a fully retarded position and the second cam lobe is in a fully retarded position. 
     
     
         18 . The method of  claim 16 , wherein a maximum advanced condition for displacement of the engine valve is defined when the first cam lobe is in a fully advanced position and the second cam lobe is in a fully advanced position. 
     
     
         19 . The method of  claim 16 , wherein a maximum opening duration of the engine valve is defined when the first cam lobe is in a fully advanced position and the second cam lobe is in a fully retarded position. 
     
     
         20 . The method of  claim 11 , wherein the displacing the engine valve from the closed position to the open position at the second valve lift profile includes the first cam lobe being engaged with a first end of the valve lift mechanism and the second cam lobe being engaged with a second end of the valve lift mechanism, the engagement between the first and second cam lobes and the valve lift mechanism rotationally displacing the valve lift mechanism about a pivot located between the first and second ends of the valve lift mechanism to provide the second valve lift profile.