Using valve timing to improve engine acoustics

Abstract

A method for improving the operation of an internal combustion engine implementing cylinder deactivation is described. Generally, the pattern of combustion events that are fired and skipped together with the geometry of the exhaust and/or intake system can create unpleasant acoustic issues. By slightly altering the timing of the cylinder intake and exhaust valves, these acoustic issues can be mitigated. The valve timing can be altered on a combustion event by combustion event basis. Alternatively, valve timing for different groups of cylinders can be modified together.

What is claimed is: 
     
         1 . A method of controlling sound of an engine having a crankshaft, a camshaft and a plurality of cylinders, each cylinder having an associated piston that is driven by the crankshaft, an associated exhaust valve, and an associated exhaust path length, wherein the respective exhaust path lengths associated with at least some of the plurality of cylinders differ and wherein at least some of the exhaust valves are driven by the camshaft, the method comprising:
 operating an engine in a skip fire mode; and   dynamically varying a phase of the camshaft between different exhaust events during a sequence of skip fire operation in a manner that at least partially compensates for differences in the exhaust path lengths associated with fired cylinders to thereby help suppress audible beats that would otherwise occur in the event that the camshaft phase was held substantially constant during the sequence of skip fire operation.   
     
     
         2 . A method as recited in  claim 1  wherein the camshaft phase is further based at least in part on the current engine speed. 
     
     
         3 . A method as recited in  claim 2  wherein the camshaft phase is further based at least in part on estimated exhaust gas temperature. 
     
     
         4 . A method of controlling sound of an engine having a crankshaft and a plurality of cylinders, each cylinder having an associated piston that is driven by the crankshaft, an associated exhaust valve and an associated exhaust path length, wherein the respective exhaust path lengths associated with at least some of the plurality of cylinders differ, the method comprising:
 operating the engine in a skip fire mode; and   dynamically varying the relative timing of the exhaust valve opening events relative to crankshaft angle between different cylinder exhaust events during skip fire operation.   
     
     
         5 . A method as recited in  claim 4  wherein the dynamic varying of the relative timing of the exhaust valve opening events is arranged to at least partially compensate for acoustic delays caused by the different effective exhaust path lengths. 
     
     
         6 . A method as recited in  claim 4  wherein the dynamic varying of the relative timing of the exhaust valve opening events is arranged to shape the exhaust noises in a desired manner. 
     
     
         7 . A method as recited in  claim 6  wherein the engine acoustics are shaped in a manner that suppresses audible beats that would otherwise occur in the event that all cylinders fired during a sequence of skip fire operation were fired at a similar relative exhaust valve opening timing. 
     
     
         8 . A method as recited in  claim 4  wherein the dynamic varying of the relative timing of the exhaust valve opening events occurs while the engine is operated at a firing fraction or firing pattern selected from a predetermined group of firing fractions or firing patterns. 
     
     
         9 . A method as recited in  claim 4  wherein
 the engine has eight cylinders arranged in two banks; and 
 the dynamic varying of the relative timing of the exhaust valve opening events occurs while the engine is operated at a firing fraction selected from the group consisting of ⅓, ⅔, ⅕, ⅖, ⅗, ⅘ and ½. 
 
     
     
         10 . A method as recited in  claim 4  further comprising:
 determining a desired baseline valve timing based at least in part on current engine operating conditions; 
 determining an exhaust timing adjustment for a particular exhaust event relative to the baseline valve timing; and 
 adjusting the exhaust valve timing for the particular exhaust event in accordance with the determined adjustment. 
 
     
     
         11 . A method as recited in  claim 10  wherein the exhaust valve timing adjustment is based, at least in part, on the relative effective exhaust path length of the cylinder associated with the exhaust event. 
     
     
         12 . A method as recited in  claim 11  wherein the exhaust valve timing adjustment is further based at least in part on the current engine speed. 
     
     
         13 . A method as recited in  claim 11  wherein the exhaust valve timing adjustment is further based at least in part on estimated exhaust gas temperature. 
     
     
         14 . A method as recited in  claim 6  wherein the engine acoustics are shaped in a manner that produces a desired engine rumble. 
     
     
         15 . A method as recited in  claim 4  further comprising altering at least one additional engine parameter such that the torque generated by each fired cylinder is substantially constant, wherein the at least one additional engine parameter includes an engine parameter selected from the group consisting of: intake valve timing, throttle position, fuel injection parameters and spark timing. 
     
     
         16 . A method of controlling acoustic characteristics of an engine having a plurality of cylinders, a crankshaft, a camshaft and a cam phaser, the method comprising applying an periodic signal to the cam phaser to adjust the phase of the camshaft relative to the crankshaft, wherein the periodic signal has a frequency that substantially corresponds to a characteristic acoustic frequency associated with a current operational condition of the engine and wherein the periodic signal is arranged to help suppress such acoustic frequency. 
     
     
         17 . A method as recited in  claim 16  wherein the periodic signal is selected from the group consisting of:
 a sinusoidal signal; 
 a triangular signal; and 
 a rectangular signal. 
 
     
     
         18 . An engine comprising:
 a crankshaft;   at least one camshaft;   a plurality of cylinders, each cylinder having an associated piston that is driven by the crankshaft and an associated exhaust valve driven by the at least one camshaft;   at least one exhaust manifold; and   an exhaust pipe that receives exhaust gases expelled from the cylinders through the at least one exhaust manifold, each cylinder having an associated exhaust path length from the cylinder through the at least one exhaust manifold to the exhaust pipe and wherein the respective exhaust path lengths associated with at least some of the plurality of cylinders differ; and   wherein the at least one camshaft includes a plurality of exhaust valve cam lobes, each exhaust valve cam lobe being arranged to actuate an associated exhaust valve, wherein the phases of the exhaust valve cam lobes relative to their associated pistons vary in accordance with the exhaust path length associated with their respective cylinders such that the sound associated with each exhaust event exits the exhaust path in a more evenly spaced manner than would occur in the event that the phases of the exhaust valve cam lobes were consistent relative to their associated pistons.   
     
     
         19 . An engine as recited in  claim 18  wherein
 the plurality of cylinders are arranged into first and second cylinder banks; 
 the at least one camshaft consists of a first camshaft and a second camshaft, the first camshaft being associated with the first cylinder bank and the second camshaft being associated with the second cylinder bank; 
 the at least one exhaust manifold consists of a first exhaust manifold and a second exhaust manifold, the first exhaust manifold being associated with the first cylinder bank and the second exhaust manifold being associated with the second cylinder bank; 
 a Y-pipe intermediate between the exhaust manifolds and the exhaust pipe, wherein a first exhaust path length between the first exhaust manifold and the exhaust pipe is greater than a second exhaust path length between the second exhaust manifold and the exhaust pipe; and 
 wherein respective phases of the first and second camshafts are offset from one another. 
 
     
     
         20 . An engine as recited in  claim 19  wherein the camshaft offset includes a static offset.