Variable valve-timing, in a broad array of forms, has become almost a standard feature in new engines, helping them achieve both greater fuel efficiency and more power across the engine speed range.
Chevrolet's 2014 Impala, which will arrive early next year, adds another dimension to that technology in its Ecotec 2.5-litre four-cylinder engine.
Called Intake Valve Lift Control (IVLC), it adds variable valve-lift to the valvetrain control repertoire, thus enabling variation of valve lift, duration and timing over a wide range of engine operation.
By reducing the valve opening at low speeds and loads, such systems help reduce what are known as pumping losses – power wasted internally just to keep the engine turning – thus improving fuel efficiency, while still permitting full valve opening and power output when needed for higher speeds and loads.
It's not a new concept. It is already a feature in several engines – primarily but not exclusively in premium-priced models – identified by such brand names as MultiAir, Valvematic, Valvetronic, Variable Valve Event and Lift (VVEL), VarioCam Plus and others.
In the Chevy application, IVLC provides two operating modes – low-lift and high-lift.
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 speeds or under heavy loads, providing the full output capability of the engine.
The engine employs an all-new rocker arm that switches between low- and high-lift intake cam profiles to achieve the variable- lift function. The mechanism is actuated by an oil control valve through a dual-feed stationary hydraulic lash adjuster.
GM says it is the first of its kind for low friction roller-type finger-follower valvetrains in gasoline engines. The engine’s computer continuously selects the preferred lift profile based on conditions such as engine speed and load.
"Intake Valve Lift Control works so seamlessly drivers aren’t likely to notice it at all," according to Mike Anderson, GM global chief engineer for Ecotec engines.
The new 2.5-litre Ecotec III four-cylinder engine, with an estimated output of 195 horsepower, is one of three engine choices offered in the new Impala, all of which feature direct injection.
An Ecotec 2.4L engine, with an estimated power rating of 182 horsepower, is matched with GM's eAssist system to enable an auto-stop-start system and provide a small electrical assist in certain conditions.
Also available is a 3.6L V-6, with an estimated output of 303 horsepower. All three engines are mated to six-speed automatic transmissions.