General Motors announced its first V-6 application of fuel-saving Active Fuel Management™ on the 3.9L V-6 offered in the 2007 Chevy Impala, and E85 ethanol fuel capability on the 3.9L V-6 offered in ’07 Chevy Uplander fleet models.
“The application of Active Fuel Management™ (AFM) and E85 ethanol offers customers more choices when it comes to selecting efficient, fuel-conscious vehicles,” said Dr. Gary Horvat, assistant chief engineer, GM Powertrain HVV6 engines. “E85 fuel reduces the need for petroleum and helps reduce greenhouse gas emissions, while AFM offers improved fuel economy over comparable, non-AFM engines.”
Preliminary testing of the 2007 Chevy Impala equipped with the 3.9L V-6 with AFM indicates an estimated 20 mpg in the city and 29 mpg on the highway – improvements of approximately 5.5 percent and 7.5 percent, 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 fuel-saving 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.
The E85-capable version of the 3.9L engine enables customers of Uplander fleet vehicles to use a renewable, domestically produced fuel that produces fewer emissions. E85 is made of 85 percent ethanol and 15 percent gasoline. GM vehicles with E85 capability can run on 100 percent gasoline or on E85 ethanol fuel or any combination of the two.
“GM has nearly 2 million flex-fuel vehicles on North American roads, and will offer 14 E85-compatible vehicles in 2007,” said Dr. Horvat.
The 3.9L V-6 is part of GM’s family of sophisticated, high-value V-6 engines. In addition to AFM and E85 capability, it features variable valve timing (VVT) – a first for cam-in-block V-6 engines (recognized by Popular Mechanics with a “Breakthrough Technology Award” in 2005.) Along with optimizing performance and economy, the VVT operation helps the engine maintain an adequate torque load to maximize the benefits of AFM’s fuel-saving mode.
Active Fuel Management details
Introduced as displacement on demand approximately three years ago on GM’s Gen IV V-8 engine, Active Fuel Management ™ was adapted to the unique performance and balance characteristics of a six-cylinder engine. As with AFM on V-8 engines, half of the 3.9L’s cylinders are deactivated during fuel-saving mode.
Fuel savings are realized whenever the engine switches to three-cylinder operation, with greater fuel economy benefits realized during longer highway drives, as the engine is able to stay in fuel-saving mode for longer durations. Complementing the fuel-saving benefit of AFM, the 3.9L also delivers strong performance. It is rated at 233 horsepower (174 kW) and 240 lb.-ft. of torque (325 Nm).*
A new, sophisticated E38 engine controller determines when to deactivate cylinders, allowing the engine to maintain vehicle speed in lighter-load conditions such as highway cruising. The changeover process is seamless and imperceptible. When the cylinders are deactivated the 3.9L 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 key to AFM’s imperceptible operation is a set of special two-stage hydraulic valve lifters, which allows 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 3.9L’s exclusive 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.
Family traits
GM’s latest generation of 60-degree, high-value V-6 engines is the first cam-in-block engine family to incorporate variable valve timing, which optimizes performance and economy and promotes lower emissions at every rpm level.
The high-value engine family shares a cylinder block casting and new head design. They feature more than 80-percent common components, but the 3.9L engine has a longer-stroke crankshaft to increase displacement. Technical highlights include:
-Iron cylinder block with offset cylinder bores
-Die-cast aluminum structural oil pan
-Aluminum cylinder heads with larger valves
-Steel crankshaft
-Cast aluminum pistons with polymer coating
-Oil piston coolers on all cylinders
-Electronically controlled “dual equal” cam phasing
-Equal-length intake manifold
-Electronic throttle control
-58X Quick Sync ignition
-Powerful engine controller
-Acoustic engine cover reduces NVH
Along with AFM, the most significant technological feature of the new 3.9L V-6 is the adaptation of variable valve timing. The 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 award-winning “assembled-camshaft” design pioneered 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 unique camshaft, and a powerful 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.
Unexpected refinements
The 3.9L V-6 incorporates a host of features and refinements typically reserved for high-cost premium engines:
-Oil piston coolers – Every cylinder has piston oil squirters that ensure optimal lubrication and cooling.
-Multilayer steel (MLS) head gaskets – These premium gaskets offer great durability over conventional graphite gaskets and were validated to 150,000 miles.
-58X Quick Sync ignition – The 3.9L V-6’s direct ignition system uses a sensor to more accurately determine the position of the crankshaft, ensuring extremely accurate ignition performance.
-Aluminum intake system – The upper and lower plenums of the equal-length intake manifold are made from cast aluminum, which offers better NVH and heat absorption characteristics than typical composite plastic intakes.
-Electronic throttle control (ETC) – Throttle operation is handled by more accurate electronic signals, eliminating the need for conventional throttle cables. Cruise control functions are incorporated with ETC, reducing underhood complexity. The engine draws air through a 72-mm single-bore throttle body.
-Multec 3.5 fuel injectors – Part of the engine’s returnless fuel system, these next-generation fuel injectors have improved hot fuel handling characteristics and improved plug resistance. Injectors in E85-capable engines have a diamond-like coating on the injector valve.
The 3.9L V-6 also incorporates long-life components such as 100,000-mile iridium-tip spark plugs and coolant, as well as premium gaskets and sealers that help ensure maintenance-free operation. The GM Oil Life System (GMOLS) also is standard.
GMOLS can extend the intervals between oil changes and reduce the amount of oil an owner buys over the operating life of the vehicle. With GMOLS, the need for an oil change is determined by an algorithm that measures engine starts, temperature and other factors. An indicator on the instrument panel illuminates when it’s time for an oil change.
Balance and power
The 3.9L V-6 engine represents an all-new engine design, but incorporates some familiar and well-regarded attributes, including a 60-degree “V” configuration. The 60-degree configuration is naturally balanced, ensuring drivetrain smoothness and eliminating the need for costly balance shafts. The relatively narrow 60-degree V also makes the engine more compact for a variety of applications.
This new engine differs from previous GM 60-degree designs with its offset cylinder bores, meaning the intersection of the cylinder bores’ centerline is not at the crankshaft centerline. Instead, the intersection is 3 mm below the crankshaft axis. This allows packaging room for the wider bores – 99 mm (3.90-in.) – as well as the engine’s longer stroke.
A “U”-shaped coolant flow system is used in the 3.9L engine. With it, coolant follows a specific path: It enters the engine at the front of the block and is carried to the back, before flowing into the rear of the cylinder head. As the coolant enters the rear of the cylinder head it flows forward, completing a U-shaped path that delivers more uniform cooling than the previous engine.
The water pump is mounted approximately 4 inches lower in the coolant’s path, which helps ensure steady flow if the system loses a small quantity of coolant. The new cooling system design also incorporates a coolant crossover at the front of the engine and requires no coolant to enter the intake manifold.
Engineers also placed the thermostat on the inlet side of the system, which allows the engine – and the vehicle’s interior – to warm up more quickly in cold weather. Also, the coolant system has an on-engine fill point. It is located at the high point in the system (near the power steering pump), easing the task of adding coolant because air cannot be trapped.
SPECIFICATIONS: 3.9L V-6 (LZ8)
Assembly site:
Tonawanda, NY
Application:
Chevrolet Impala
Type:
3.9L V-6 with variable valve timing, Active Fuel Management™ (LZ8)
Displacement (cu in/ cc):
237 / 3880
Bore x stroke (in x mm):
3.90 x 3.31 / 99 x 84
Block material:
cast iron
Main bearing caps
powder metal (1, 2, 3); cast nodular iron (4)
Cylinder head material:
cast aluminum
Intake manifold:
cast aluminum
Exhaust manifolds:
high-silicon molybdenum, cast nodular iron
Compression ratio:
9.8:1
Valve configuration:
overhead valves (2 valves per cylinder)
Valve lifters:
hydraulic roller
Firing order:
1 - 2 - 3 - 4 - 5 – 6
Fuel system:
sequential fuel injection
Horsepower (hp / kW):
233 / 174 @ 5600 rpm*
Torque (lb-ft / Nm):
240 / 325 @ 4000 rpm*
Fuel shut-off:
6400 rpm
Emissions controls:
close-coupled catalytic converter, evaporative system, positive crankcase ventilation
Crankshaft:
steel
Camshaft:
assembled steel
Connecting rods:
forged powder metal
Additional features:
electronic throttle control, dual equal continuously variable valve timing, roller rocker arms, pressure-actuated piston cooling jets, extended-life spark plugs, extended-life coolant, GM Oil Life System, oil level sensor, extended-life accessory drive belt
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SPECIFICATIONS: 3.9L V-6 (LGD)
Assembly site:
Ramos Arizpe, Mexico
Application:
Chevrolet Uplander (fleet sales only)
Type:
3.9L V-6 with E85 ethanol capability ( LGD )
Displacement (cu in/ cc):
238 / 3880
Bore x stroke (in x mm):
3.90 x 3.31 / 99 x 84
Block material:
cast iron
Main bearing caps
powder metal (1, 2, 3); cast iron (4)
Cylinder head material:
aluminum
Intake manifold:
cast aluminum
Exhaust manifolds:
high-silicon molybdenum, cast nodular iron
Compression ratio:
9.8:1
Valve configuration:
overhead valves (2 valves per cylinder)
Valve lifters:
hydraulic roller
Firing order:
1 - 2 - 3 - 4 - 5 – 6
Fuel system:
sequential fuel injection
Fuel type:
E85 and regular unleaded
Horsepower (hp / kW)
240 / 179 @ 6000 rpm*
Torque (lb-ft / Nm):
240 / 325 @ 4800 rpm*
Fuel shut-off:
6000 rpm
Emissions controls:
catalytic converter, evaporative system, positive crankcase ventilation
Crankshaft:
steel
Camshaft:
assembled steel
Connecting rods:
forged powder metal
Additional features:
E85 flex-fuel capable, 58X crankshaft, cam phaser, U-flow cooling
For release 18-5-2006
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-----The orginal Mr.Goodwrench on the JBO since 11/99-----
