In a Family Way

Once the preserve of luxury car powerplants, variable valve timing is now spreading to more mainstream engines. Case in point: the arrival of General Motors’ new ‘high feature’ global V-6 engine family, the first engine from GM to feature VVT on both intake and exhaust camshafts.

The first of this V-6 family, a 3.6L will make its debut in Cadillac’s 2004 CTS, replacing its existing, U.K.-sourced 3.2L V-6. The new 255 hp CTS motor is one of several versions of the modular V-6, which will also come in 2.8L and 3.2L displacements, to be used in major markets worldwide. Engine size can be expanded to 3.8L, or as large as 4.0L when the cylinder liners are eliminated in favor of bore coatings.
 
Versions of the engine will be both naturally aspirated and turbocharged and applications will include front-, rear- and all-wheeldrive, as well as hybrid vehicles.
 
One key to the new engine family’s success, maintains GM, is that it will be competitive with the best in the V-6 class, such as the Honda/Acura 3.2L and Toyota/Lexus 3.0L units, yet be built at a lower cost. All GM’s V-6s will share the following features: aluminum construction, dual overhead camshafts, fourvalve- per-cylinder valvetrain, roller-finger followers, continuously variable cam phasing, electronic throttle control, forged-steel crankshaft, piston-cooling oil jets, coolant-loss protection software, GM’s oil-life system, 32 bit microprocessor and coil-on-plug ignition.
 

A valve in the dualstage manifold closes to boost cylinder charging in the low- to midspeed range. It opens at higher speeds to feed all cylinders from a common larger plenum.

GM says the output of the most powerful variant of the new engine family will exceed 370 hp, with torque in excess of 350 lbs.-ft.
 
Work on the new V-6 family started in 1999, and was completed in record time, says Tim Cyrus global V-6 chief engineer.
 
“The goals for the engine were industry leading reliability, flexibility, package size, pleasibility, efficiency and value,” Cyrus says. The engine can be easily integrated into most platforms, has industry leading NVH and performance with three discrete combustion systems MPFI, SIDI and turbo.”

Importantly, the V-6 engine architecture was designed to incorporate different options, in order to create a broad range of configurations. As well as normally aspirated/ sequential port fuel injection ‘foundation’ architecture, there are two potential major variants. One is a spark-ignition direct-injection (SIDI) V-6 of either 2.8L or 3.2L displacement. To account for differing market regulations and conditions, particularly in Europe, the engine design can accommodate both stratified-charge (lean-burn) and stoichiometric- charge SIDI architectures. Also in the pipeline are turbocharged 2.8L or 3.2L variants, with a variety of power and torque outputs depending on specific content.
 
As well as its adaptability, the key feature of GM’s V-6 family is its use of variable valve timing. Moving to full VVT eliminates the traditional compromise in engine design between power and torque outputs, and also improves fuel economy and lowers emissions. In the case of the 3.6L engine, the improvement in torque output is notable: 90 percent of the 252 lbs-ft. peak torque is available across a broad operating range, from 1,600 to 5,800 rpm.

Compared to an existing GM double overhead cam V-6, the 3.6L develops 20 percent more peak power, a 13 percent increase in peak torque — and a 24 percent increase in torque-integral, or the amount of torque available at most points throughout the rpm range.

“Flexibility was very important,” says Bob Jacques, base engine design system engineer. “We insisted on going after high performance and high refinement at the same time.”

A 32-bit micro-hybrid engine control unit embeds all of the necessary electronic circuitry on a four layer substrate that reduces the size of the unit. The new design can be engine mounted, freeing up valuable engine compartment space.

The four-cam continuously variable cam phasing system is electronically controlled and hydraulically actuated. The phasers allow intake cam adjustment through 50 degrees of crankshaft rotation and 50 degrees for exhaust-cam adjustment.

An added benefit of the VVT system is that it allowed for the elimination of the exhaust gas recirculation system, thus reducing weight and complexity.

The V-6’s intake system includes a dualstage variable manifold. A valve in the manifold changes the plenum volume available for resonance tuning of the inlet flow path. When the valve is shut, the cylinders feed from two separate plenums. In this mode the system boosts cylinder charging in the low- to midspeed range. At higher engine speeds, the valve opens and the cylinders all feed from a common larger plenum.

Another significant technical advance is the V-6’s 32-bit micro-hybrid engine control unit, which GM claims is the most powerful currently used in the industry. The ECU design embeds all of the necessary electronic circuitry on a four-layer ‘sandwich’ substrate that reduces the size of the control unit. More robust and resistant to vibration than previous ECUs, the new design can be engine mounted. This move frees valuable space in the engine bay and eliminates attachment problems at the assembly plant.
 

The four-cam continuously variable cam phasing system is electronically controlled and hydraulically actuated. The phasers allow intake cam adjustment through 50 degrees of crankshaft rotation and 50 degrees for exhaust-cam adjustment.

One function of the ECU is torque-based engine control strategy. Engine output for the driver’s desired throttle opening is determined by the ECU. The torque-based strategy calculates optimal throttle position, variable intake manifold position, continuously variable cam phasing positions and various other operational inputs and then translates that information into an ideal throttle position. GM says the torque-based engine control strategy is superior to early electronically controlled throttle-based engine-management systems that relied only on the throttle position sensor to govern throttle opening.

In terms of detail refinements, Jacques says the target was to be class leading. “We went after all the benchmarks,” he says. “You name it — if there is a good V-6 out there, we found out how and why it was good.”

Refinement measures include specially isolated cam covers, which incorporate an isolated gasket around the cover perimeter and radial lip seals at the tubes through which each spark plug is inserted. These components decouple the cam cover from vibration created by the combustion process.

The structural aluminum oil pan is attached by a full-circle mounting that enhances bending stiffness. Specially contrived curves on the major panel surfaces and the sidewalls mitigate ‘drumming’ from the oil pan.

The engine front cover has internal damping plates that quell vibrations caused by the engine. The steel plates, made in two different thicknesses ‘tune’ at differing frequency from the aluminum front cover; the frequency separation dampens noise output.

While several rival Japanese V-6 engines use belt cam drives, GM Powertrain chose chain drives for the new engine family. “We went with chains for longer life,” says Jacques. “The Japanese engines have used belts because they are less expensive and quieter, but they are also moving to chains now.” In the case of GM’s new V-6, Jacques says the noise of the camshaft drive chain engaging the sprocket teeth is reduced by use of molded-rubber ‘cushion rings’ on the crankshaft sprocket.

GM plans to assemble its new V-6 engine family for all global applications at plants in St. Catharines, Ontario, Canada and Port Melbourne, Victoria, Australia.

Beyond the Cadillac CTS, initial North American market applications for the 3.6L V- 6 include Cadillac’s forthcoming mid-sized Rendezvous.

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Engine specifications: 2004 3.6L Global V-6 Engine (LY7)
Configuration	3.6L 60-degree DOHC V-6
Peak Power (SAE net)	Estimated 255 hp @ 6,500 rpm
Peak Torque	250 lb.-ft./339 Nm @ 2,800 rpm; (90% of peak produced from 1,600 rpm to 5,800 rpm)
Displacement (cc)	3,564
Bore x Stroke	94 mm x 85.6 mm
Valvetrain	Dual overhead camshaft 4-valve-per-cylinder Roller-finger followers valvetrain Hydraulic lash adjusters Four-cam continuously variable cam phasing Two-stage roller-chain camshaft drive
Variable Cam Timing	Intake: 132 degrees ATDC initial timing 50 crankshaft degrees advance authority
Exhaust	111 degrees BTDC initial timing 50 crankshaft degrees retard authority
Compression Ratio	10.2:1
Bore Centers	103 mm
Firing Order	1-2-3-4-5-6
Fuel Shutoff	6,700 rpm
Engine Idle Speed	600 rpm
Fuel System	Sequential port fuel injection (returnless)
Engine Management	Torque-based; Bosch Motronic ME 9 32-bit micro-hybrid controller
Intake Manifold	Dual-plenum, equal-length with 2-position variable volume control (resonance tuned)
Throttle	68-mm single bore; electronic control (ETC)
Ignition	Individual coil-on-plug; individual cylinder knock control
Fuel Requirement	Premium fuel recommended
Emissions Controls	Dual close-coupled catalytic converters (1.15L ultra-thinwall ceramic) Positive crankcase ventilation (PCV) Intake- and exhaust-cam phasers (EGR) Evaporative emissions system
Assembly Site	St. Catharines, Ontario, Canada Port Melbourne, Victoria, Australia
Material Applications Block Material	Aluminum, precision sand-cast 319 with cast-in-place iron liners
Cylinder Head Material	Aluminum, semi-permanent mold 319
Intake Manifold: Upper	Aluminum, sand-cast 319
Lower	Aluminum, 356-T6
Exhaust Manifold	High-silicon moly cast iron
Camshaft Covers	Injection compression thermoset composite; vibration isolated
Front Cover	Diecast 380 aluminum; internal multilayer damping panels
Crankshaft	Forged steel
Connecting Rods	Sinterforged steel
Pistons	Aluminum, polymer-coated skirts, full-floating wristpins
Main Bearing Caps	6 bolt caps, copper-infiltrated sintered steel
Oil Pan	Structural diecast aluminum, steel windage and baffle plates
Additional features: Pressure-actuated piston-cooling oil jets Extended-life sparkplugs, coolant, accessory belts Cartridge-style, top-access oil filter Oil-level sensor Wide-range oxygen sensors