Variable Valve Timing Improves Drivability &Fuel Efficiency While Reducing Emissions
By General Motors of Canada - Athletes understand that proper breathing is critical to maintaining peak performance under all conditions and so do Chevrolet powertrain engineers. Getting air in and exhaust gases out of the combustion chamber under all speeds and driving conditions is essential to outstanding drivability and fuel efficiency with low emissions.
"Whether powered by four, six or eight cylinders, virtually every current Chevrolet car and truck, from compact cars including the award-winning Cruze to the full-size Suburban SUV, features variable valve timing (VVT) on its engine to optimize its breathing," said Sam Winegarden, General Motors executive director of Global Engine Engineering.
The camshafts are driven by chains from the crankshaft to keep the valve opening in sync with the motion of the pistons in the cylinders.
Through continuous adjustments of the camshaft phasing, engineers can achieve smoother idle control without sacrificing the ability to breathe at higher engine speeds. This ability contributes to the 3.6-litre V6 in the Chevrolet Camaro generating 312 horsepower while getting a fuel consumption rating of 6.6L/100km on the highway.
Chevrolet's VVT system uses a hydraulic mechanism to twist the camshaft relative to the crankshaft position so that the valves can be opened and closed earlier or later. On dual overhead cam engines such as the Ecotec inline-four and the 3.0 and 3.6-litre V6, the intake and exhaust cams can be adjusted independently, allowing the valve overlap - the time that intake and exhaust valves are both open - to be varied as well.
The 60 degrees of camshaft adjustment available on the turbocharged 1.4-litre Ecotec that powers the Cruze enabled engineers to eliminate the conventional exhaust gas recirculation system to simplify the overall engine packaging - the way the engine fits in the car - and still reduce emissions.
"Bookending the Chevy lineup, the VVT-equipped Cruze Eco achieves the best in class highway fuel consumption rating of 4.6L/100km while the full-size Silverado XFE pickup is rated at an estimated 9.1L/100km on the highway" said Winegarden.
"Whether powered by four, six or eight cylinders, virtually every current Chevrolet car and truck, from compact cars including the award-winning Cruze to the full-size Suburban SUV, features variable valve timing (VVT) on its engine to optimize its breathing," said Sam Winegarden, General Motors executive director of Global Engine Engineering.
The camshafts are driven by chains from the crankshaft to keep the valve opening in sync with the motion of the pistons in the cylinders.
Through continuous adjustments of the camshaft phasing, engineers can achieve smoother idle control without sacrificing the ability to breathe at higher engine speeds. This ability contributes to the 3.6-litre V6 in the Chevrolet Camaro generating 312 horsepower while getting a fuel consumption rating of 6.6L/100km on the highway.
Chevrolet's VVT system uses a hydraulic mechanism to twist the camshaft relative to the crankshaft position so that the valves can be opened and closed earlier or later. On dual overhead cam engines such as the Ecotec inline-four and the 3.0 and 3.6-litre V6, the intake and exhaust cams can be adjusted independently, allowing the valve overlap - the time that intake and exhaust valves are both open - to be varied as well.
The 60 degrees of camshaft adjustment available on the turbocharged 1.4-litre Ecotec that powers the Cruze enabled engineers to eliminate the conventional exhaust gas recirculation system to simplify the overall engine packaging - the way the engine fits in the car - and still reduce emissions.
"Bookending the Chevy lineup, the VVT-equipped Cruze Eco achieves the best in class highway fuel consumption rating of 4.6L/100km while the full-size Silverado XFE pickup is rated at an estimated 9.1L/100km on the highway" said Winegarden.
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