GM Powertrain today introduced three new versions of existing engine models: a 3.6-liter V-6 gasoline engine with direct injection and variable valve timing (VVT); its first V-6 application of Active Fuel Management (cylinder deactivation) on the 3.9-liter V-6 for 2007 Chevy Impala; and E85 ethanol fuel capability on the 3.9-liter V-6 offered in 2007 Chevy Uplander fleet models.
The 3.6L VVT DI engine reduces fuel consumption by up to 3% while increasing power by 15%. The 3.9-liter AFM application improves fuel economy by an estimated 5.5% (from 22 mpg EPA combined to a projected 23.2 mpg combined).
This brings the total of new or significantly revised engines for model year 2007 to 19.
The 3.6-liter VVT DI. GM will apply a version of its 3.6-liter V-6 gasoline engine with direct injection and variable valve timing (VVT) technologies in the 2008 model year. The company will announce a specific vehicle target later this year.
The application of direct injection technology to the 3.6-liter VVT engine contributes greatly to a 15% increase in horsepower over the current levels that range from 240 hp to 267 hp; an 8% increase in torque, and up to a 3% improvement in brake-specific fuel consumption (BSFC). An approximate 25% reduction in cold-start hydrocarbon emissions is also achieved.
GM projects that by 2010 one out of every six GM vehicles in North America will be equipped with a direct injection engine.
Direct injection delivers precisely metered fuel directly to the combustion chamber, producing a cooling effect in the chamber. Cooling the incoming air charge enables a higher compression ratio (greater than 11.0:1 in the case of the 3.6), which also improves engine efficiency. Less fuel is required to produce the equivalent horsepower of a conventional port injection combustion system.
The 3.6-liter VVT with direct injection will be our highest specific output non-turbocharged V-6 engine, as well as one of the most fuel-efficient offerings in our high-feature family.—Tim Cyrus, chief engineer for high feature V-6 and Northstar V-8 engines
The 3.6-liter is GM’s third engine with gasoline direct injection. The announcement of the 3.6L VVT V-6 with direct injection comes after the introduction of GM Powertrain’s Ecotec 2.0-liter four-cylinder Turbo engine with direct injection on the 2007 Saturn Sky Red Line and Pontiac Solstice GXP roadsters. GM has been delivering a naturally-aspirated Ecotec 2.2-liter direct injection engine on Opel models in Europe since 2004.
The fuel injectors in the gasoline direct injection system are located beneath the intake ports. The intake ports only transfer air, unlike port fuel injection, which flows air and fuel, thus increasing efficiency.
Direct injection requires higher fuel pressure than conventional fuel injected engines and an 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 VVT DI is based on GM Powertrain’s 60-degree dual-overhead cam (DOHC) V-6 engine. The 3.6-liter V-6 VVT DI employs four-cam phasing to change the timing of valve operation as operating conditions such as rpm and engine load vary.
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 also reduces 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 25% reduction in cold-start hydrocarbon emissions brought on 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).
3.9-liter Active Fuel Management. The new 3.9-liter engine with AFM is GM’s first V-6 application of its cylinder deactivation technology. (GM had pushed back the introduction of the V-6 AFM engine back to the 2007 model year to do additional fine-tuning on noise and vibration.) (Earlier post.)
Preliminary testing of the 2007 Chevy Impala equipped with the 3.9-liter V-6 with AFM indicates an estimated 20 mpg in the city and 29 mpg on the highway—improvements of approximately 5.5% and 7.5%, respectively.
Active Fuel Management enables the engine to automatically operate on half of the engine’s cylinders under light load conditions, improving efficiency by reducing fuel consumption when the cylinders are deactivated.
GM offers this technology in 11 vehicles for 2007, including trucks and SUVs – more than any other automaker. The Impala is GM’s first V-6 application of AFM in North America. GM also is launching a 3.0L V-6 with AFM in China that will debut in the Buick LaCrosse this summer.
A new engine controller determines when to deactivate cylinders, allowing the engine to maintain vehicle speed in lighter-load conditions such as highway cruising. When the cylinders are deactivated, the engine effectively operates as an inline three-cylinder engine, with cylinders 1, 3 and 5 deactivated on the left cylinder bank. The engine returns to V-6 mode the instant the controller determines the vehicle speed or load requires additional power.
|The special hydraulically-activated de-ac lifters that enable GM’s Displacement on Demand.|
GM uses two-stage hydraulic valve lifters which allow the lifters of deactivated cylinders to operate without actuating the valves. The lifters have inner and outer bodies, which normally operate as a single unit. When the engine controller determines cylinder deactivation conditions are optimal, the outer body moves independently of the inner body on the disabled cylinders’ lifters.
The outer body moves in conjunction with camshaft actuation, but the inner body does not move, holding the pushrod in place. This prevents the pushrod from actuating the valve, thereby halting the combustion process. Also, fuel supply to the fuel injectors is halted while the cylinders are deactivated.
Solenoids in the Lifter Oil Manifold Assembly (LOMA) operate to deliver high-pressure oil to the switching lifters, activating a release pin to separate the inner and outer bodies. Oil circulation and pressure do not vary regardless of the engine’s operational mode. Lifter design and pushrod length are the same for every cylinder, but camshaft lobe profiles differ for cylinders designated to be deactivated.
Because the noise and vibration characteristics are different between a V-6 and the effective inline three-cylinder operation when the 3.9L is in fuel-saving mode, engineers tuned the engine and exhaust system to maintain consistent operational sound and feel. For example, the alternator features a unique decoupling clutch that instantly adjusts tension on the accessory drive belt when the engine switches from six- to three-cylinder operation.
The 3.9-liter’s cam-in-block variable valve timing technology also works synergistically with Active Fuel Management, as the cam phaser enables the engine to produce maximum torque during three-cylinder operation. This allows the engine to remains in fuel-saving mode longer.
The VVT system incorporates a vane-type camshaft phaser that changes the angular orientation of the camshaft, thereby adjusting the timing of the intake and exhaust valves to optimize performance and economy, and help lower emissions. It offers infinitely variable valve timing in relation to the crankshaft.
The cam phasing creates “dual equal” valve timing adjustments. In other words, the intake valves and exhaust valves are varied at the same time and at the same rate. The cam phaser vane is attached to the camshaft on the front journal—a technique made easier by the assembled-camshaft design developed by General Motors.
With this design, separate camshaft lobes are installed on a hollow camshaft tube rather than the traditional method of grinding a camshaft from a single piece of stock.
Hydraulic roller lifters with low-friction followers complement the camshaft, and the engine controller enables the engine’s cam phasing. The system’s demand for precise camshaft position information is met with a unique, cam target ring with four equally spaced segments that communicate the camshaft’s position quickly and accurately. Also, a leaf spring-type tensioner is used on the timing chain to ensure precise tension.
The 3.9L V-6’s camshaft is unique and matched to the engine’s bore-and-stroke characteristics. It is different, for example, than the camshaft in the 3.5L V-6.