General Motors is introducing its new 3.6L V-6 gasoline engine with direct injection and variable valve timing (VVT) technologies in the 2008 Cadillac STS.
The new 3.6-liter all-aluminum dual overhead cam V-6 gasoline engine with direct injection and variable valve timing is GM's most powerful V-6 offering in North America and in other markets around the globe. It is of particular significance for power-conscious customers looking for great performance, improved fuel economy and lower emissions.
The new 3.6L V-6 (LLT) engine delivers outstanding performance ratings. Standard in the 2008 Cadillac STS, the engine is SAE certified and delivers 302 hp (225 kW) at 6300 rpm* and 272 lb.-ft. (369 Nm) of torque at 5200 rpm.*
"Our goal was to deliver an engine with outstanding power and improved efficiency, while providing a quiet and pleasant driving experience for Cadillac customers," said Tim Cyrus, chief engineer for high-feature V-6 and Northstar V-8 engines. "It's the latest example of our strategy to continue to reduce emissions and improve fuel economy without sacrificing performance."
The 3.6L V-6 engine is GM's third engine variant offered with direct injection technology.
With direct injection technology, fuel is sprayed directly into the engine cylinder where it is mixed with air. As the fuel vaporizes in the cylinder, the air and fuel mixture is cooled. This enables the use of a higher compression ratio in the combustion chamber, 11.3:1, which improves engine performance and efficiency.
On cold starts, direct injection can be controlled to create a richer air/fuel mixture around the spark plug, making it easier to ignite in a cold engine. This results in a smoother operation and an approximate 25-percent reduction in cold-start hydrocarbon emissions during the cold-start and warm-up.
Direct injection requires higher fuel pressure than conventional fuel-injected engines, and the engine-driven high-pressure fuel pump is used to supply up to 1,740 psi (120 bar) of pressure. The system regulates lower fuel pressure at idle - approximately 508 psi (35 bar) and higher pressure at wide-open throttle. The exhaust cam-driven high-pressure pump works in conjunction with a conventional fuel tank-mounted supply pump.
The 3.6-liter V-6 also features the U.S. automotive industry's first isolated fuel-injector system. This helps reduce the overall engine noise, providing customers a pleasant driving experience.
Four-cam phasing
In addition to direct injection, variable valve timing also helps reduce exhaust emissions and improve performance and fuel economy by optimizing the phasing of the intake and exhaust valves relative to the crankshaft position at all operating conditions. The result is linear delivery of torque, with near-peak levels over a broad rpm range, and high specific output (maximum horsepower per liter of displacement) without sacrificing overall engine response and driveability.
Cam phasing pays big dividends in reducing exhaust emissions by optimizing exhaust valve overlap and eliminating the need for a separate exhaust gas recirculation (EGR) system.
By closing the exhaust valves late at appropriate times, the cam phasers allow the engine to draw the desired amount of exhaust gas back into the combustion chamber, reducing unburned hydrocarbon emissions. The return of exhaust gases also decreases peak temperatures, which contributes to the reduction of oxides of nitrogen (NOx) emissions. In tandem with the dramatic 25-percent reduction in cold-start hydrocarbon emissions enabled by direct injection, the 3.6-liter VVT DI V-6 surpasses all emissions mandates, and does so without complex, weight-increasing emissions control systems such as EGR and air injection reaction (AIR).
3.6-liter VVT DI features
The 3.6-liter VVT DI is based on GM Powertrain's sophisticated 60-degree dual overhead cam (DOHC) V-6 engine. It is the latest member of a growing family of GM Powertrain V-6 engines developed for applications around the world, drawing on the best practices and creative expertise of GM's technical centers in Australia, Germany, North America and Sweden.
Features found on the 3.6-liter VVT DI include:
* Aluminum engine block and cylinder heads
* Dual overhead cams with four valves per cylinder and silent chain primary drive
* High-pressure, engine-driven fuel pump
* Advanced multi-outlet fuel injectors developed to withstand high pressure and heat
* Isolated fuel injector system
* Stainless steel, variable pressure fuel rail
* Four-cam phasing (variable valve timing)
* 11.3:1 compression ratio
* Cast-aluminum pistons with floating wrist pins and oil squirters
* Polymer coated piston skirts
* Forged steel crankshaft
* Sinter-forged connecting rods
* Structural cast-aluminum oil pan with steel baffles
* Electronic throttle control with integrated cruise control
* Coil-on-plug ignition
* Advanced direct injection capable engine control module (ECM)
* Optimized exhaust manifolds with close-coupled catalytic converters
* Fully isolated composite camshaft covers
* Outstanding noise, vibration and harshness control
* Maximum durability with minimal maintenance
* Common manufacturing practices for efficiency and exceptional quality
By the end of 2008, GM forecasts it will produce as many as 200,000 vehicles globally with direct injection technology, and projects that by 2010, one of every six GM vehicles in North America will be equipped with a direct injection engine.