REVOLUTION AND EVOLUTION UNITE IN POWERFUL NEW 3900 V-6
PONTIAC, Mich. – Thomas Edison said, “Genius is one percent inspiration, 99 percent perspiration.” GM Powertrain engineers have slightly rearranged Edison’s ratio, using equal parts of inspired new engineering and exacting evolution of existing technology to develop the new 240-horsepower 3900 V-6.
“The application of elegant-yet-simple technology to a proven architecture allowed us to give the new 3900 V-6 premium-engine attributes, such as variable valve timing and active intake, at a cost more customers can afford,” said **** Michalski, chief engineer for 60-degree OHV V-6 engines. “The 3900 will give GM car buyers a terrific combination of high power density, outstanding low-speed torque and excellent fuel economy.”
The 3900, the latest in GM’s “high-value” family of 60-degree overhead valve V-6 engines, benefits from two significant new technology applications that simultaneously deliver increased power and markedly reduced fuel consumption and emissions.
The 3.9-liter is GM’s first V-6 to use the innovative Displacement on Demand (DOD) cylinder-deactivation system. DOD significantly reduces overall fuel consumption by allowing the engine to operate on just half of its cylinders when driving conditions don’t require full power. GM will first launch the technology on the Gen IV Vortec 5300 V-8 engine and will add it to the 3900 V-6 in 2005. The 3900 will debut without DOD in the all-new, midsize Pontiac G6.
But DOD isn’t the new 3900’s only claim to fame: it also is the first GM overhead-valve (OHV) engine to employ variable valve timing – a torque- and efficiency-enhancing feature until now typically reserved for more expensive overhead-camshaft (OHC) architecture engines. Engines with “fixed” valve timing compromise between conflicting performance demands in order to provide an acceptable overall balance of engine operation. The 3900’s variable valve timing system largely eliminates those compromises, allowing the engine to produce more torque in a wider range of engine operation – while concurrently reducing emissions and improving fuel economy.
The two new technologies combine to give the 3900 V-6 high specific output and torque across a broad operating range, along with a lusty dose of torque that peaks at a low, satisfying engine speed. The 3900 is estimated to develop 240 horsepower at 5900 rpm and 245 lb.-ft. of torque at just 2800 rpm. Moreover, thanks to the 3900’s torque-enhancing technologies, 90 percent of peak torque is available from 1800 rpm to 5800 rpm, enhancing the engine’s driveability and performance “feel.”
Improved fuel economy
The new 3900 V-6 (LZ8) is a 3.9-liter, two-valves-per-cylinder OHV V-6 that is most closely related to the 3500 V-6 (LX9) launched for the 2004 model year Chevrolet Malibu. The largest of GM’s expanding family of 60-degree V-6 engines, the 3900 achieves its 3900 cc of displacement via an increase in bore size to 99 mm from the 3500 V-6’s 94 mm – and also incorporates several important new innovations and upgrades.
The 3900 is GM Powertrain’s first V-6 engine to use the unique Displacement on Demand (DOD) technology. The Displacement on Demand system was designed to markedly improve the fuel efficiency of six- and eight-cylinder engines without sacrificing performance. The system boosts aggregate fuel economy by between 6 percent and 8 percent.
Michalski said the 3900’s increased displacement fits like glove-in-hand with Displacement on Demand: “A bigger engine is better when you want to maximize the amount of time the engine spends in three-cylinder operation,” he explained.
Typically, increasing an engine’s displacement also increases its fuel consumption – but not so when an engine sports Displacement on Demand. Enlarging the 3900’s displacement by 400 cc actually improves its overall fuel economy because the larger displacement translates to a greater amount of time the engine can operate in its ultra-efficient three-cylinder mode. As it turns out, bigger really is better when using Displacement on Demand.
The Displacement on Demand system is designed to enhance fuel economy in a totally unobtrusive manner. The 3900 always starts on six cylinders, and always uses six cylinders when the powertrain controller determines the vehicle’s speed or load requires additional power. But since most routine driving requires only a fraction of an engine’s total power, once underway the 3900-equipped vehicle will seamlessly transition to three-cylinder mode. If, for example, the driver requires higher performance or the vehicle is negotiating a steep grade, the 3900 instantaneously reverts to all-cylinder operation.
In light-load driving situations, Displacement on Demand maximizes each of the three operating cylinder’s thermal, mechanical and pumping efficiencies, rather than sending fuel to six cylinders that aren’t doing as much work. And when the cylinders themselves are optimally sized, as with the new 3900, Displacement on Demand will instruct the engine to operate more of the time in three-cylinder mode.
Attaining the engine displacement to maximize Displacement on Demand’s advantages created its own unique challenge, however. Michalski said that to attain the 3.9 liters of displacement Powertrain engineers deemed ideal, the 3900’s larger cylinder bores had to be offset 1.5 mm from the crankshaft center line so that the cylinders did not interfere with the camshaft. This required development of a new engine-block design for the 3900.
New electromechanical controls
In typical two-valves-per-cylinder OHV engines, the camshaft has a lobe corresponding to each cylinder’s intake and exhaust valve. As the camshaft turns, the lobe contacts a hydraulic roller valve lifter, which drives the pushrod that translates the camshaft’s rotating motion to the linear motion that opens each valve.
But in Displacement on Demand-equipped engines, half of the cylinders have unique two-piece valve lifters, which incorporate two telescoping sections that can collapse into one another. An oil-pressure-activated locking pin in the lifters is engaged or disengaged – on command from the engine control module (ECM) – according to whether Displacement on Demand operation is warranted.
For normal six-cylinder operation with the 3900 V-6, the locking pin solidly fixes the valve lifters’ two telescoping sections, meaning that as the camshaft lobe contacts the lifter, the intake and exhaust valves are opened. To deactivate three of the six cylinders, hydraulic pressure is used to unlock the pin, enabling the valve lifters’ two sections to freely telescope into one another. Thus as the camshaft lobe contacts the “deactivated” valve lifter, one section compresses into the other and the camshaft motion is not translated to the pushrod, meaning that cylinder’s intake and exhaust valves remain closed.
Thanks to the split-second electromechanical control available from the 3900 V-6’s powerful ECM – as well as the ECM’s ability to electronically “speak” with many other engine- and transmission-control sensors – cylinder deactivation and reactivation can occur in milliseconds. As a result, the transition between six-cylinder and three-cylinder operation is seamless and imperceptible to vehicle occupants.
Variable valve timing delivers new flexibility
The new 3900 V-6 also boasts GM’s first use of variable valve timing for an OHV V-6 engine. The variable valve timing system uses an electronically controlled hydraulic gear-driven camshaft phaser to alter the relationship of the camshaft as much as 40 degrees overall (25 degrees retard and 15 degrees advance) relative to the crankshaft.
The 3900’s camshaft phaser provides for infinitely variable adjustment of camshaft timing with respect to the crankshaft. By electronically controlling the camshaft, the optimum location can be selected for various engine operating conditions, maximizing torque and horsepower outputs.
Variable valve timing also presents significant emissions benefits, said Dr. Gary Horvat, assistant chief engineer, 60-degree OHV V-6 engines. The 3900’s precision valve control means engineers could eliminate the external exhaust gas recirculation (EGR) system. In addition, maximum exhaust-valve opening helps the 3900 to quickly warm the exhaust catalyst, improving cold-start emissions.
“The system simplifies things greatly for emissions calibration,” said Horvat. “We have considerably more control over output – and a better overall emissions ‘profile’ – as a result of going to variable valve timing.”
The 3900’s variable valve timing is coupled with another important new feature: a dual-path, active intake manifold. The active manifold is an engine feature usually found only on high-cost, premium European performance cars, but the new manifold design is standard with the 3900 V-6.
“The variable intake manifold is a significant low-speed torque ‘enhancer’ for the 3900,” said Michalski. “It gives the 3900 a broader torque curve that retains higher specific torque output across the engine speed range.” As with Displacement on Demand, the active intake manifold is designed to make the most of the 3900 V-6’s increased displacement.
The active air intake optimizes incoming airflow through a valve in the intake manifold. The valve creates longer or shorter intake tracts that correspond to desired engine-performance parameters. At low engine speeds, the valve creates a longer path for intake air, enhancing combustion efficiency and torque output. At higher engine speeds, the valve opens, creating a shorter air path for maximum power production.
Although the new 3900 V-6 was designed as a high-output, performance-oriented engine, it hardly foregoes the traits of reliability, durability and refinement that are characteristics of GM Powertrain’s “high-value” engine families.
The 3900 incorporates many of the same features and components that have made the 3100, 3400 and 3500 OHV V-6s mainstays for numerous GM vehicles. For example, because of the processing demands of new features like variable camshaft timing and the active intake manifold, the 3900’s engine control module is the latest, most-powerful ECM currently used by GM. The Motorola-based E67 has 32-bit processing power and incorporates 32 megabytes of Burst Flash memory, 32 kilobytes of external RAM and 36 kilobytes of internal RAM, as well as a high-speed CAN bus to deliver optimal networking capability.
Other 3900 V-6 technical highlights:
Electronic throttle control. The ETC system eliminates the physical connection between the accelerator pedal and the engine throttle. This well-proven “by-wire” control allows for remarkably precise engine control and response, while simultaneously enhancing the engine’s interface with Displacement on Demand, variable valve timing, and active intake systems.
A power- and efficiency-enhancing 9.8:1 compression ratio. Although engines with compression ratios exceeding approximately 9.5:1 often require premium unleaded fuel to prohibit engine “knock,” the 3900 delivers full performance on regular unleaded gasoline.
Oil jets spray the underside of each piston with a continuous bath of cooling oil, increasing longevity and reducing engine-operating temperatures. For high-output engines like the 3900, piston-cooling jets help to ensure long-term durability.
A high-capacity oil pump delivers appropriate amounts of lubrication to the 3900’s new oil systems: Displacement on Demand, camshaft phaser and the piston-cooling jets.
Low-friction roller cam followers for valve lifters. This premium component cuts friction and wear by providing a rolling rather than a sliding surface between the camshaft and the valve lifter.
The Quick Sync 58X ignition allows the ECM to instantly discern the exact location of each piston when the engine is started. This enables the ECM to immediately select optimum fuel, spark and intake parameters to reduce startup emissions. The Quick Sync ignition also provides for more-refined engine starting.
The 3900 V-6 will be produced at GM Powertrain’s Tonawanda, N.Y., assembly plant.