|IVLC uses an all-new rocker arm that switches between low- and high-lift intake cam profiles. The mechanism is actuated by an oil control valve through a dual-feed stationary hydraulic lash adjuster. Click to enlarge.|
The new 2014 Chevrolet Impala offers as one of its three engine options a four-cylinder Ecotec 2.5L engine, featuring the debut of a new advanced variable valvetrain technology—Intake Valve Lift Control (IVLC, earlier post)—and improved fuel economy. The EPA estimated fuel economy for the 2014 Impala with the new 2.5L engine is 21 mpg city and 31 mpg highway (11.2 and 7.6 l/100 km, respectively).
The 2.5L engine, which delivers SAE-certified 196 horsepower (146 kW) and 186 lb-ft of torque (252 N·m), achieves variable valve lift using an all-new rocker arm that switches between low and high lift intake cam profiles.
The mechanism is actuated by an oil control valve through a dual-feed stationary hydraulic lash adjuster. It is the first of its kind for low friction roller-type finger-follower valvetrains in gasoline engines, GM says. The engine’s computer continuously selects the optimal lift profile based on conditions such as engine speed and load.
When the technology operates in low-lift mode, the engine pumps only the air it needs to meet the driver’s demand. The system switches to high-lift mode at higher engine speeds or under heavy loads, providing the full output capability of the engine.
|Low-lift profile. Click to enlarge.||High-lift profile. Click to enlarge.|
Intake Valve Lift Control works so seamlessly drivers aren’t likely to notice it at all. What they will notice is a fuel economy improvement of up to one mile per gallon.—Mike Anderson, General Motors’ global chief engineer for Ecotec engines
Quiet. The redesigned large sedan’s 2.5L engine with direct injection is engineered to be one of the quietest and most refined in the segment. The development team reduced engine noise intensity by 40% by specifically targeting the 2.5L’s noise frequency signature. They pushed radiated noises into a higher frequency range well above 2,000 hertz, which is more pleasing to the ear—particularly in the high-load operating ranges where engine sound is most intense.
The refinement-enhancing changes and improvements over previous Ecotec engines ranged from the comparatively simple—such as integrating a sound-absorbing cover into the intake manifold and specifying quieter drive chains—to more fundamental architecture items, such as relocating the balance shafts from the cylinder block to a cassette within the oil pan.
Impala’s passengers get a quieter driving experience due in part to active noise-canceling technology and a more refined sound as the engine revs to its 7,000-rpm peak.
Chevrolet expects the 2.5L model to be a popular choice among Impala buyers. The other engine options are a 3.6L V-6 and the Ecotec 2.4L with eAssist. More than two-thirds of Chevrolet cars sold in the first quarter of 2013 had a four-cylinder engine.