General Motors’ European unit Opel has announced details of its new mid-size petrol engine family.
The new 1.6-litre, four-cylinder, SIDI (spark ignition direct injection) Ecotec Turbo engines, the start of a renewal of the automaker’s powertrains (a new 1.6 diesel is on the way to replace the current 1.7) offers CO2 emissions and fuel consumption cut 13% compared to the previous engine while peak torque and power have been increased up to 33%.
The new engine line is a 1.6 litre eco turbo with 125kW/170hp and 280Nm peak torque plus a performance turbo variant offering 147kW/200hp and 300Nm peak torque. The 170 hp engine has been developed with fuel economy, high low-end torque and elasticity in mind, while the performance of the 200 hp unit makes it the claimed benchmark in its class.
Launch of the new engine family – developed at Opel’s base in Ruesselsheim, Germany – will begin in early 2013.
GM has designed a new cylinder block able to withstand peak cylinder pressure of 130 bar. Cast iron was selected as the preferred material for the cylinder block in combination with an aluminium bedplate.
Key development objectives for refinement were low overall radiated noise and vibration levels, and no unusual sounds. Achieving these goals enabled vehicle integration that can tune primary engine orders in the induction and exhaust systems to meet specific vehicle objectives. The excellent acoustic and vibration performance of the engine is crowned by the cam cover, which is decoupled from the cylinder head via specific fasteners and a sealing system designed for high temperatures, due to the nearby turbocharger.
As a result of these sound-engineering measures, the customer perceives quiet and smooth idling, no unusual noises throughout the operating range, and a pleasant sound quality even at high speeds and loads, Opel claimed.
The SIDI Ecotec is the only engine in its class to offer balance shafts. The two balance shafts are inserted in tunnels from the rear end of the cylinder block and are driven by an inverted-tooth chain. The exhaust side shaft features cast iron gears to reverse rotational direction of the exhaust shaft. The optional system offsets the vibrations inherent in the design of four cylinder engines and thus helps to maximise comfort and reduce noise to a minimum.
The design and sizing of the turbocharging system plays a key role in enabling downsized engines to deliver excellent performance and drivability, while meeting CO2 targets.
Smaller displacement engines with high specific torque and boost levels require fast transient response, especially at low engine speeds, in order to be a valid replacement for larger displacement engines. Thanks to its specially designed turbines, the midsize gas engine’s turbocharger provides response that is usually generated by twin-scroll turbines on larger engines.
The engine retains the proven concept of a turbine-integrated exhaust manifold. This design was chosen instead of a twin-scroll concept because of its packaging and manufacturing advantages. Although the turbocharger has identical interfaces, each engine variant features a dedicated turbo aerodynamic.
The compressors are designed to deliver high low-end torque without generating noticeable aerodynamic sounds. Combined with low and high-pressure resonators, air-borne noises effects like hiss, pulsation and blade-pass noise are almost completely suppressed. With additional aspects like air handling, duct design and control strategies for let-off noise, the new engine benefits from an aggressive boost strategy without the typically associated turbo related acoustic degradation.
Compared to the predecessor engine the new SIDI Ecotec turbo delivers a claimed “remarkable improvement in elasticity”, for example, reducing the time for 80km/h to 120km/h fifth-gear acceleration by about 20%.
In addition to refinement and performance, high fuel economy and low emissions were the main development objectives of the new 1.6-litre engines. Engineers therefore selected a central direct-injection fuel system, for optimum fuel efficiency and minimal emissions.
The central location of spark plug and injector over the combustion chamber, and their orientation parallel to the crankshaft, forms a compact package with the capability to support homogeneous and stratified engine operation.
The valve train is operated by low-friction hydraulic roller finger followers and driven by a timing chain with a maintenance-free hydraulic tensioner. Acoustics are further improved by the inverted teeth of the cam drive chain. For mass reduction the midsize gasoline engine features a two-piece crankcase design, supported at the lower end by a die-cast aluminium bedplate.
The cylinder block is manufactured using an innovative thin-wall casting method. This allows the integration of different functional features directly into the raw block and offers potential to reduce production time.
The engine uses a broached press-fit between the cylinder block and the bedplate instead of dowels, in order to optimise the main bearing shape as well as its positional accuracy. The structural design considers the engine’s use in a variety of vehicle applications, allowing minimum integration effort and consistent part interchangeability.
The structural benefit derived from the combination of a forged steel crankshaft, optimised main bearing journal diameters, and iron main bearing cap inserts results in minimised noise and vibration at mid and high rpm.
Two different pistons have been designed for the Eco and Performance turbo engines. Each has a dedicated top land including a small bowl. A cast iron ring carrier adapted to the high cylinder pressures is common to each piston. The PVD coated first piston ring is an additional friction-reduction measure.
Production of the new 1.6 litre SIDI Ecotec Turbo engine alongside the other new engine families will be at the Szentgotthard plant in Hungary and will begin in late 2012. The factory uses the flex plant concept which enables petrol and diesel engines to be built on a shared assembly line.