OE powertrain execs map out fuel-economy strategies
Dan Kapp presents Ford approach to meeting fuel economy standards for 2017 at an SAE 2011 World Congress panel on Tuesday. Other participants were (from left) Uwe Grebe of GM, Bob Lee of Chrysler, Gary Rogers of FEV Inc., Hans Hohenner of BMW Group, and John Juriga of Hyundai-Kia North American Technical Center.
U.S. fuel-economy regulations call for 35.5 mpg by 2017, or is it 34.1 mpg? Or maybe it’s 250 g/mi CO2.
Actually, the regulations are based on complex formulas derived from a “vehicle footprint” (track multiplied by wheelbase). So although the federal government has an overall industry fleet target based on 250 g/mi, every manufacturer has a different number to meet based on the types of vehicles it sells. Representatives of General Motors, Chrysler, Ford, BMW, and Hyundai-Kia each explained their somewhat different focus, even if the general direction is the same. They spoke on Tuesday at an SAE 2011 World Congress panel discussion led by Gary Rogers, President and CEO of FEV Inc., on the powertrains that will get the industry to compliance in time.
The 250 g/mi requirement translates roughly to 35.5 mpg (a U.S. EPA figure), but it includes credits for a change to a lower global warming refrigerant or other air-conditioning system modifications. The 34.1 mpg is a NHTSA (National Highway Traffic Safety Administration) figure and is tied to fuel economy changes alone. There are fuel-economy curves based on the footprint of a manufacturer’s fleet.
“All roads are open,” said Uwe Grebe, Executive Director, GM Powertrain Global Advanced Engineering. In addition to widespread use of transmissions with eight speeds or more, GM will continue with cylinder deactivation.
Company engineers will increase use of variable valve activation, engine downsizing and boosting—including two-stage turbocharging. It will also employ advanced combustion systems—particularly direct injection—for gasoline engines. Grebe did not exclude HCCI (homogeneous charge compression ignition), although other panelists said the light load region for this technology might be shrinking as a result of other changes.
Perhaps the GM vehicle technology introduction that garnered the most attention since the Chevrolet Volt has been the E-Assist for the 2012 Buick LaCrosse. Grebe explained it is a much higher-performance version of GM’s BAS (belt alternator-starter) system, and said it increases fuel economy 25% over the conventional 2.4-L four-cylinder—from 19 mpg city/30 mpg highway to 25/37.
E-Assist has a 115-V lithium-ion battery pack (vs. 42-V nickel metal hydride for the previous BAS) and a 15-hp (11 kW)/79 lb·ft. (107 N·m) electric motor that provides increased acceleration assist and regenerative braking vs. the previous BAS. Because of the powerful motor, LaCrosse can use an aggressive deceleration-to-stop fuel cutoff strategy as well as idle stop-start.
GM also will deploy idle stop-start on conventional 12-V models, Grebe said.
Diesels are an important part of the picture for GM, Grebe noted. He said the company has advanced engineering programs under way for improvements in aftertreatment systems, fuel charging, and combustion—the latter including new fuel injectors, turbochargers, and exhaust gas recirculation.
Ford’s branded version of engine downsizing with turbo boosting-“Ecoboost,” is a key part of the company’s strategy, but “too much downsizing actually can degrade fuel economy,” said Dan Kapp, Director of Powertrain Research and Advanced Engineering.
He told the audience that the 3.5-L turbo “Ecoboost” V-6 is migrating through product lines. It will be joined by a four-cylinder 2.0-L, then a 1.6-L, and eventually a 1.3-L, the latter limited to use with 98 RON (road octane number) gasoline because the higher loading makes knock a limiting performance factor, Kapp said. The larger-displacement engines can protect for 91 RON by retarding spark and still maintain adequate performance.
The increased use of direct injection, he said, by improving restartabilty, is an enabler for the rollout of idle stop-start, which Ford will begin in U.S. production next year.
Kapp added that platform changes, such as body-on-frame SUVs to unit body crossovers, would produce weight savings of 250-750 lb (113.4-340.2 kg), which would help maintain performance through the engine downsizing program.
Chrysler’s Bob Lee said “bang for the buck” is the company mantra, and that “some very complex computer models” for meeting the 2017 fuel-economy standards have been developed. As the potential effects of the Fiat ownership are worked into the picture, those complex models keep changing, added Lee, who serves as Vice President, Engine, Electrified Propulsion, and Advanced Powertrain at Chrysler.
Chrysler’s use of vehicle electrification will be “sparing.” There will be an electric vehicle for 2012, he said, and some CNG (compressed natural gas) applications.
The Fiat Multi-Air system, now being incorporated into a Chrysler-built version of the 1.4-L Fiat 500 engine for a Dodge-branded model to be introduced this year, does provide a low-speed torque advantage, Lee said. It also reduces pumping losses, but this is less of an advantage on Chrysler V6/V8 engines that will be equipped with eight- or nine-speed automatics because they will be running in low-load operation much of the time.
“If we reduce pumping losses with the transmission, then something that does it another way, such as Multi-Air, doesn’t accomplish as much,” he explained. Further, some V8s have cylinder deactivation, another light-load fuel saver.
Chrysler has a sharp focus on matching powertrain with vehicle footprint, said Lee, adding that the company “must get vehicle energy demand right. Efficiency is generally gained at the expense of performance… but you can’t just cut performance because of customer demand.”
The performance demanded by the customer is a particularly critical item for BMW Group, observed panelist Hans Hohenner, General Manager and Development Drivetrain Product Manager.
He pointed to BMW’s engine downsizing program for gasoline engines, which is replacing the 3.0-L inline six, rated at 300 hp (221 kw), with a 2.0-L four. If naturally aspirated, the latter would not perform to BMW owner expectations. But with a twin-scroll turbo and variable valve train, it is rated at approximately 350 hp (257 kW), Hohenner noted. The engine also will use idle stop-start. Accessory loads are reduced, with an electric water pump and A/C compressor decoupling.
BMW will emphasize scalable hybrid architectures, and cover the bases from “mild” hybrids (idle stop-start and regenerative braking) to full hybrid electrics vehicles, plug-in hybrids. and battery-electric vehicles. Even the gasoline V8 will get the twin-turbo treatment and idle stop-start to boost fuel economy.
Diesels also have been a successful part of the BMW model mix, their premium reputation and performance having overcome pricing issues.
Hyundai has to appeal to a value-oriented customer, which “means the technology has to work hard,” said John Juriga, Director, North American Powertrain, Hyundai-Kia America Technical Center. Further, the company’s product line footprint (no large vehicles sold here) means it must reach a fleet average of 37 mpg, he said.
Despite that higher requirement, there will be no E85’s and no diesels. And although Hyundai and Kia will have hybrid-electric vehicles, plug-in, and battery-electric vehicles, “we won’t be relying on them to meet the fuel economy regulations,” Juriga said.
Thanks to an engine downsizing and turbo program already under way, the company’s fleet average is over 34 mpg now, he said, “and we don’t intend to just meet the 37 mpg; we’ll exceed it by 2016.” The primary technologies will be:
• Reduced pumping losses with eight-speed automatics (and beyond) and low-pressure EGR
• Reduced friction from DLC (diamond-like coated) roller bearings, specially-coated piston rings (coated via physical vapor deposition), and higher-temperature (110ºC/230ºF.) coolant thermostats
• Exhaust heat recovery systems to improve cold start
Original article available here: http://www.sae.org/mags/AEI/9688