DETROIT – Along with performance and efficiency, the new Ecotec engine family is designed to deliver excellent refinement, with low vibration and noise levels. Engineers targeted every aspect of the architecture – reciprocating components, fuel system and engine management functions – in the quest for class-leading smoothness and quietness.
“From the outset, the noise and vibration requirements for the new Ecotec family were targeted at class-leading,” said Randy Guild, noise and vibration engineer for global Ecotec engines. “Because we started with a clean-sheet design process, every component from the cylinder block to the fuel injectors played a role in achieving segment-class refinement. They all had a noise-and-vibration target to meet and weren’t approved for production until they achieved it.”
While the degree of refinement may be subjective, factors that contribute to it are measurable – such as an engine’s noise frequency signature, for example. Pushing radiated noises from the architecture into a higher frequency range well above 2,000 hertz results in sound that is more pleasing to the ear, particularly in the high-load/high-rpm operating ranges where sound is the most intensive with small-displacement engines.
Arriving at a pleasing engine sound with low vibration required more than bolting on a sound-absorbing engine cover to dampen noise. All of the engine components, including structural elements such as an acoustically optimized cylinder block, were evaluated on their performance and interaction with other components.
“Refinement for the new Ecotec architecture is much more than the sum of its parts,” said Guild. “Through extensive modeling and exhaustive bench testing with pre-production engines, each structural element and every engine component was designed to work harmoniously to achieve the program’s sound quality and vibration goals.”
In other words, good enough wasn’t good enough. Parts were tested over and again with changes until the entire engine assembly hit the refinement target.
Engineers quantified the new Ecotec’s noise and vibration performance by measuring it against competitors, including testing that shows the new Ecotec 1.4L turbocharged engine, which will be offered in the 2015 next-generation Chevrolet Cruze in China, has up to 50 percent lower noise intensity (up to 6 decibels quieter) than Volkswagen/Audi’s 1.4L EA211 four-cylinder.
The modularity of the new Ecotec architecture and the economies of scale that come with its reduced complexity enabled greater applications of premium design features such as an inverted-tooth camshaft drive chain that’s common to all variants. It not only contributes to lower noise and vibration, it enhances durability – attributes that can add up to higher perceived value for customers.
In fact, the inverted-tooth drive chain is one of the elements that help the new Ecotec 1.0L turbocharged three-cylinder, which will be offered with the Opel ADAM in Europe, achieve up to 25 percent lower noise intensity (up to 3 decibels quieter) than the 1.0L turbo three-cylinder engine in the Ford Fiesta.
“The inherent qualities of a three-cylinder’s operation are challenging, but by employing a balance shaft and features such as the inverted-tooth chain, we were able to achieve the sound qualities of a refined four-cylinder,” said Guild. “We believe it will set a new benchmark for small-engine refinement – and delight customers who may not have believed a small-displacement engine like this could deliver such a premium driving experience.”
The all-new Ecotec engines have a quiet component set that contributes to smoothness and quietness, including:
Engine block and bedplate: The new Ecotec architecture’s refinement is rooted in its all-aluminum cylinder block, which is acoustically designed to reduce airborne and structure-borne operating noise. The structure is so good at quelling noise and vibration, the need to mask the transfer of engine noise with in-car sound insulation and other attenuation components is significantly reduced, which helps reduce the vehicle’s weight.
A bedplate provides stiffness to the bottom of the cylinder block and incorporates the main bearing caps – components used to secure the crankshaft within the block. Iron inserts cast into the bedplate enhance the structure at the main bearings, for greater smoothness and quietness. The insert material ensures close main bearing tolerances over a wide range of engine operating temperatures, for quieter engine lower-end noise.
Forged crankshaft: In turbocharged applications, a forged steel crankshaft is used to support the greater combustion pressures of forced induction with excellent durability, as well as enhance refinement with vibration-resistant performance – particularly at mid- and high-rpm levels, when the engine is producing maximum boost. The crankshaft is used with main bearings featuring tight tolerances that also contribute to good sound quality.
Oil jets: Piston-cooling oil jets not only enhance performance and durability, they provide an extra layer of oil on the cylinder walls and piston wristpins at start-up, which dampens noise emanating from the pistons.
Aluminum oil pan with a steel sump: A two-piece oil pan is composed of a structural, die-cast aluminum upper section, where it attaches to the cylinder block. The lower section features a coated, stamped steel sump– a design that helps reduce engine noise, because the steel section dampens noise better than an all-aluminum pan.
In-pan oil pump assembly and balance shaft: Mounting the oil pump assembly inside the oil pan reduces noise from the front cover area – an aluminum-intensive area that transmits noise – and minimizes the potential for pump cavitation noise.
On three-cylinder variants, a balance shaft is used to achieve four-cylinder-like sound and vibration qualities. It is mounted inside the oil pan and operates with the oil pump.
Inverted-tooth camshaft drive chain: The camshaft drive chain is optimized for low sound levels through an inverted-tooth design, which is significantly quieter than a roller-type chain. As its name implies, an inverted-tooth chain has teeth on its links – two-pin rolling pivot joints – that essentially wrap around the gear sprocket to take up virtually all the tension. This allows for smoother meshing of the chain links to the sprocket teeth, the cause of most noise in chain drive systems. The chain-to-sprocket tooth impact is greatly reduced with the inverted-tooth design (also known as a silent chain drive), substantially reducing noise and enhancing durability.
Camshaft drive system: In addition to the inverted-tooth camshaft drive chain, the entire chain-drive architecture, including its tensioning, wrap and guides, is designed for reduced overall noise radiation and the elimination of many perceived abnormal sounds. The tensioner is designed to never require adjustment, ensuring optimal chain tension and low noise performance for the life of the engine.
Structural camshaft and engine front covers: As a cast-aluminum part mounted on the very top of the engine assembly, the camshaft cover can be a significant source of noise. That’s not the case with the new Ecotec family, thanks to a structural cover design that mounts directly to the engine to enhance its overall stiffness – an attribute that helps push the engine’s sound frequency above 2,000 hertz. This frequency is attenuated easily with the acoustic treatment of the top engine cover, providing a lower overall radiated engine noise level as well as sound quality that is pleasing to the ear.
Similar to the structural camshaft cover, the front cover, which covers both the camshaft drive system and balancer drive systems, was designed with ribbing and other features to provide a stiffer, more rigid and quieter cover that contributes to lower engine noise.
Front-end accessory drive: The front-end accessory drive features an overriding alternator coupler to remove the effect of crankshaft oscillations. Along with refinement benefits, it also allows a reduction in tensioning force to reduce friction levels and improve efficiency.
Isolated fuel rail and fuel injectors: To reduce the noise associated with the high-pressure fuel system of direct injections, the injectors are suspended and the fuel rail is attached to the cylinder head with rubber-isolated, compression-limiting mounting provisions. This ensures there is no metal-to-metal contact and prevents the transmission from pulsing energy through the engine structure. The fuel pump and fuel line are also acoustically optimized.
Quieter turbo system: On turbocharged variants, the design of the turbocharger compressor reduces the characteristic whistle or hiss sound associated with turbo systems. Passengers feel the application of power as the turbocharger produces boost, but without the typical sound associated with it.
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