Three new GM powertrains offer more power and showcase Displacement on Demand and variable valve timing technologies.
|GM’s Gen IV Vortec 5300 small-block V-8 gets the first production application of Displacement on Demand.|
At a recent GM Powertain event, Tom Stephens, group vice president, powertrain, laid out GM’s new advanced propulsion plan for the near, mid and long term.
According to Stephens, the goal of GM’s technology strategy is to reduce vehicle emissions. “If you want to have zero emissions and a huge increase in fuel economy there’s really only one answer that we’re aware of. And that lies in the hydrogen economy and the hydrogen fuel cell powered vehicle,” Stephens says.
But while GM’s ultimate goal is still to bring one million fuel cell powered vehicles to commercial market by 2010, Stephens realizes that GM needs to take integral steps on its “March to Zero” as the plan is known internally.
“It’s not enough though just to have a long term strategy,” Stephens says, “you need to have a near term and a mid-term strategy and we have those as well.”
GM’s near-term powertrain strategy is focused on improvements to its internal combustion engines, developing technologies that will enhance the fuel economy of the soft and full hybrids that make up the mid-term strategy.
“We’re after higher levels of fuel economy, power and torque, all at the same time,” says Stephens.
Stephens says that GM is looking for 60 hp per liter for naturally-aspirated engines and about 100 hp per liter for turbocharged engines. Engineers are also developing spark ignition direct injection for global applications. Cam phasers are high on GM’s list of powertrain technologies. Stephens says that by 2007, 2.5 million GM powerplants will be equipped with variable valve timing (VVT).
“In addition,” says Stephens, “we’re looking at variable induction tuning on our overhead valve engines.”
According to Stephens, displacement on demand, a fuel-saving technology that allows six and eight-cylinder engines to run on half of their cylinders in certain conditions, will be installed on two million engines annually by 2008.
In addition, the DOHC four-valve engines will benefit from two-step valve trains plus port deactivation which will find its way onto one million engines by 2006.
On the emissions side, Stephens offers that all future advanced control system algorithms will be model based. “So we can do them fast and right the first time.”
Work continues on the combustion system. Catalytic converters are being mounted closer to the engines to improve their performance and exhaust manifolds are being integrated into cylinder heads. There is also an emphasis on active intake manifolds and Stephens says, in some cases, engineers will look at integrating turbochargers into exhaust manifolds.
Consumers will get to test a few of GM’s near-term ICE strategies on three new powerplants that will be brought to market the end of this year and early next year.
GM’s first production applications of Displacement on Demand (DOD) will find its way onto the fourth generation Vortec 5300 small block V-8, standard on the 2005 Chevrolet Trailblazer EXT, GMC Envoy XL and Envoy XUV, as well as a DOD-equipped Vortec 3900 V-6, which will debut in the Pontiac G6, the Grand Am replacement due this spring. A version of the 5300, sans DOD is available now in the Buick Ranier and a non-DOD automotive application of the 5300 will debut later this year in the ’05 Corvette.
The brains behind DOD is the E40 engine controller. The controller monitors such things as oil temperature, rpm, coolant temperatures and throttle position and determines when to drop cylinders and vice versa.
The seamless shifts occur through the activation of two-stage hydraulic valve lifters. In normal mode, the inner and outer lifter sleeves are held together by a pin. DOD is activated by delivering high pressure oil to the lifters, which depress the pin and allow the outer portion of the shaft to move with the cam lobe while the inner portion doesn’t move, holding the pushrod in place. The electronic operation is achieved through the lifter oil manifold assembly (LOMA), mounted in the engine valley. The LOMA is equipped with solenoids that trigger the switching lifters.
Oil circulation and pushrod length are the same for all cylinders while camshaft lobes are customized for the deactivated cylinders. Because of the change in acoustic dynamics and vibration with the switch from four to eight cylinder mode, engineers added a pressure- activated valve in the muffler that automatically switches with the engine, adjusting the exhaust path to deliver the appropriate noise reduction.
DOD-equipped engines also have speciallytuned exhaust and engine mounts.
The engine’s electronic throttle control is designed to increase manifold pressure in DOD mode to maintain engine torque.
|The Vortec 3900 V-6 is the first General Motors overhead valve powerplant to use variable valve timing and Displacement on Demand. |
|The lifter oil manifold assembly is the heart of the Displacement on Demand. Solenoids on the unit trigger the switching filters, disabling the pushrods.|
The Gen IV Vortec 5300 shares the deep skirt engine block design of the previous GM truck engine, allowing for cross-bolted main bearings for added strength. The all-aluminum truck engine is rated at an estimated 290 hp and 325 lb.-ft. of torque in V-8 mode with no changes in towing capabilities.
The new block casting has redesigned oil galleries to meet the oiling requirements needed for DOD. The knock sensors and camshaft sensor have been moved to provide room for the new oil galleries. A higher capacity oil pump and larger coils on the coil-near-plug ignition are also need for DOD. All models now feature electronic throttle control for improved throttle response and DOD signaling. The transmission now has its own controller due to the demands that DOD puts on the ECM.
The Gen IV 5300 also carries over the iridium- tipped spark plugs, pistons with floating wrist pins, redesigned water pump and stronger E-85-compatible timing chain.Vortec 3900 V-6
According to GM, the new Vortec 3900 V-6 is a close relative of the 3500 V-6 launched in the 2004 Chevrolet Malibu. The 3900 is the first GM overhead-valve (OHV) engine to utilize variable valve timing (VVT) and displacement on demand (DOD).
Engine size was increased 400 cc with DOD in mind. GM engineers felt that the larger displacement was needed to get optimal performance in the three cylinder mode.
To keep from having to cast a new block, the larger bores in the 3900 are created by lowering the bore center on the block.
DOD works the same on the 3900 V-6 as it does on the 5300 V-8, though rather than alternating cylinders on each bank, the 3900 drops the left ban when in DOD mode. The variable valve timing system uses and electronically-controlled, hydraulic gear-driven cam phaser that can alter the relationship of the camshaft from 15 degrees retard to 25 degrees advance (40 degrees overall) relative to the crankshaft.
By using VVT, GM engineers were able to eliminate the EGR valve and also found that maximum exhaust-valve opening helped to warm the exhaust catalyst quicker, improving cold start emissions.
The VVT also works in conjunction with an active manifold. GM says that the variable intake manifold serves as a low speed torque enhancer, giving the engine a broader torque curve. A valve in the manifold creates a longer path for intake air at low speeds, enhancing combustion efficiency and torque output. At higher speed the valve opens creating a shorter air path for maximum power production.
The 3900 has GM’s latest ECM currently available. The Motorola-based E67 has 32-bit processing power and 32 megabytes of Burst Flash memory, 32 kilobytes of external RAM and 36 kilobytes of internal RAM plus a high speed CAN bus to deliver the necessary power to run VVT and the active manifold. The 3900 also has electronic throttle control that enhances the engines interface with DOD. The 3900 will be built at GM’s Tonawanda, N.Y., assembly plant.2.4L Ecotec
|The 2.4L Ecotec four-cylinder powerplant will be a performance option on the 2005 Chevrolet Cobalt, the Cavlier replacement. |
GM will also introduce variable valve timing to the Ecotec four-cylinder engine family. A 2.4L Ecotec will be an optional powerplant in the 2005 Chevrolet Cobalt.
Starting with the 2.2L variation, GM engineers increased both cylinder bore and stroke by 88mm and 98mm respectively. The engine is expected to deliver 170 hp at 6000 rpm and 170 lb.-ft. of torque over a 2400 to 5600 rpm range thanks to VVT.
The VVT system uses the same hydraulic cam phasers found on the V-6 but can alter the relationship of the intake and exhaust camshafts by as much as 50 degrees relative to the crankshaft.
The new four-banger is also equipped with electronic throttle control and shares the V-6’s E67 engine control module.
All analog engine sensors have been replaced with more accurate digital sensors and individual coil-on-plug ignition modules improve upon the two-coil “cassette” found on the original Ecotec. Twin counter-rotating balance shafts are driven by a zero-maintenance chain that also drives the camshafts and water pump.
Leveraging the experience from its NHRA front-drive drag racing programs, GM has fitted the 2.4L Ecotec with several heavy-duty components and systems.
A redesigned cylinder head is improved structurally and has a multi-layer steel gasket. There’s also a smaller, more efficient external oil cooler, new camshafts, piston-cooling oil jets that spray a continuous bath of oil on the underside of the piston reducing engine operation temperatures and an enhanced lubrication system that provides for the extra requirements of the VVT and piston-cooling jets, plus a deeper oil sump to handle the potential higher cornering forces.
The Ecotec 2.4L will be built at GM’s Spring Hill, Tenn., assembly facility.