Four stroke internal combustion engine having variable valve timing and method

Abstract

A four stroke internal combustion includes at least one cylinder and at least one intake valve associated with the cylinder. The intake valve is configured to open and close over a predetermined range of crankshaft rotation in accordance with a Miller thermodynamic cycle. An electronic controller receives at least one input signal indicative of an amount of air and/or an amount of air/fuel mixture in cylinder. The electronic controller is configured to provide a timing phase signal that operates to adjust a timing of operation of the intake valve based on the input signal(s) such that a torque output of the engine is maintained substantially constant over a predetermined range of engine speed by shifting the predetermined range of crankshaft rotation.

1 . A four stroke internal combustion engine, comprising:
 at least one cylinder having a piston reciprocable between top dead center (TDC) and bottom dead center (BDC) positions;   at least one intake valve associated with the at least one cylinder and operable by a camshaft, the at least one valve being configured to open and close over a predetermined range of crankshaft rotation, wherein the intake valve operates in accordance with a Miller thermodynamic cycle;   an electronic controller disposed to receive at least one input signal indicative of at least one of an amount of air and an amount of air/fuel mixture in the at least one cylinder;   wherein the electronic controller is configured to provide a timing phase signal that operates to adjust a timing of operation of the at least one intake valve based on the at least one input signal such that a torque output of the engine is maintained substantially constant over a predetermined range of engine speed by shifting the predetermined range of camshaft rotation with respect to a crankshaft position.   
     
     
         2 . The engine of  claim 1 , wherein the timing phase signal causes a phase shift in the predetermined range of camshaft. 
     
     
         3 . The engine of  claim 2 , further comprising a phaser associated with the camshaft and disposed to index the camshaft in response to the timing phase signal. 
     
     
         4 . The engine of  claim 1 , wherein the at least one input includes at least one of engine speed, engine load, charge air oxygen concentration, altitude, and fuel quality. 
     
     
         5 . The engine of  claim 1 , wherein a ratio of air to fuel in the at least one cylinder is maintained constant during engine operation to yield at least one of a rich-burn stoichiometric combustion and a lean burn stoichiometric combustion. 
     
     
         6 . The engine of  claim 5 , wherein the timing phase signal operates to decrease a Miller effect of the engine when at least one of the engine speed is low, the engine load is low, the altitude is high, the fuel quality is high, and the engine is in a startup mode. 
     
     
         7 . The engine of  claim 1 , wherein the engine is fueled by at least one or natural gas, propane, field gas, biogas, and producer gas. 
     
     
         8 . The engine of  claim 1 , wherein at least one of the torque output and a speed of the engine is maintained within a range of +/−10% of a target torque output value. 
     
     
         9 . The engine of  claim 1 , wherein the engine is configured to, at times, admit and compress an intake charge for combustion in the at least one cylinder that is within the range of between 20 and 80% of a total possible intake charge, which is defined as an intake charge that would have been admitted into the at least one cylinder had the intake valve been opened substantially at TDC and closed substantially at BDC during an intake stroke. 
     
     
         10 . The engine of  claim 9 , wherein a volumetric efficiency of the engine is within the range of 45-60%. 
     
     
         11 . The engine of  claim 1 , wherein the at least one cylinder is configured to operate at a compression ratio 10:1 and 15:1. 
     
     
         12 . A method for operating a four-stroke internal combustion engine, comprising:
 operating the engine at a stoichiometric air to fuel ratio and at an engine valve timing in a fashion consistent with a Miller thermodynamic combustion cycle;   receiving operating parameters at an electronic controller, the operating parameters being indicative of an amount of an air and fuel combustion mixture present in at least one engine cylinder;   processing the operating parameters in the electronic controller to determine at least one of a desired valve timing and a timing phase variation, wherein the operating parameters include at least one of engine speed, engine load, altitude, and fuel quality;   determining a valve phase signal based on at least one of the desired valve timing and the timing phase variation; and   changing a valve timing based on the valve phase signal to selectively adjust the amount of the combustion mixture such that an engine torque output is maintained substantially constant over an engine speed range.   
     
     
         13 . The method of  claim 12 , wherein the processing of the operating parameters involves determining the at least one of desired valve timing and timing phase variation based on a then-present engine speed and engine load. 
     
     
         14 . The method of  claim 13 , wherein the processing of the operating parameters involves compensating the at least one of desired valve timing and timing phase variation based on altitude. 
     
     
         15 . The method of  claim 13 , wherein the processing of the operating parameters involves compensating the at least one of desired valve timing and timing phase variation based on fuel quality. 
     
     
         16 . The method of  claim 12 , wherein changing the valve timing is accomplished by indexing a camshaft in response to the valve phase signal. 
     
     
         17 . The method of  claim 16 , wherein the valve phase signal is provided to a phaser device that operates to adjust the indexing of the camshaft in response to the valve phase signal. 
     
     
         18 . The method of  claim 12 , wherein operating the engine consistent with the Miller thermodynamic combustion cycle is accomplished by at least one of:
 maintaining at least one intake valve associated with a cylinder of the engine open beyond a BDC position of a piston such that an intake stroke is generally prolonged and a compression stroke is generally abridged under a late inlet closing (LIC) type of engine operation, and   closing the at least one intake valve before the BDC position of the piston such that the intake stroke is generally abridged and the compression stroke is generally prolonged under an early inlet closing (EIC) type of engine operation.   
     
     
         19 . The method of  claim 18 , wherein determining the at least one of desired valve timing and timing phase variation is consistent with:
 quickening the closing of the at least one intake valve when the engine is operating under a LIC type of operation, or   delaying the closing of the at least one intake valve when the engine is operating under an EIC type of operation,   such that an effect of the Miller cycle is decreased when the operating parameters are indicative of at least one of a low engine speed, a low engine load, a high altitude, or a high fuel quality, or when the engine is in a startup mode.   
     
     
         20 . The method of  claim 18 , wherein determining the at least one of desired valve timing and timing phase variation is consistent with:
 delaying the closing of the at least one intake valve when the engine is operating under a LIC type of operation, or   quickening the closing of the at least one intake valve when the engine is operating under an EIC type of operation,   such that an effect of the Miller cycle is increased when the operating parameters are indicative of at least one of a high engine speed, a high engine load, or a low fuel quality.