The Ward’s 10 Best Engines competition has recognized outstanding powertrain development for 18 years. In this installment of the 2012 Behind the 10 Best Engines series, WardsAuto looks at the development of the2.0L DOHC EcoBoost I-4.
All major auto makers are addressing consumer and government demands for improved fuel economy. Many are using a strategy that includes direct fuel injection and variable valve timing combined with turbocharged downsized engines, but none is betting on this tactic more than. And Ford wins our prize for the best name: EcoBoost.
Now WardsAuto editors have bestowed a 2012 Ward’s 10 Best Engines award on Ford’s 2.0L EcoBoost I-4, which delivers a stout 240 hp (120 hp/L) and 270 lb.-ft. (366 Nm) of torque as tested in a ’12 Ford Edge midsize cross/utility vehicle.
Editors praise the turbo I-4 for its commendable throttle response, low-friction coated piston skirts, ability to run on regular unleaded gasoline and twin independent variable camshaft timing. They averaged 24 mpg (9.8 L/100 km) over 430 miles (692 km) of “heavy-footed” driving vs. the vehicle’s touted 30-mpg (7.8 L/100-km) highway rating.
We ask Scott Makowski, program manager for Ford’s “large” I-4 engines, to fill us in on the development and key features of this EcoBoost 4-cyl., which debuted in Europe in 2010, then (in upgraded form) in the ’12 U.S. Ford Edge and Explorer.
While the 2.0L EcoBoost does share assembly and machining lines with earlier naturally aspirated Duratec I-4s, nearly every major component has been newly designed to handle the turbocharged engine’s increased power and torque, Makowski says.
In addition to fitting the engine with aturbocharger and direct-injection system, the whole crank train and just about everything else on the 2.0 L EcoBoost is upgraded for higher output.
“We changed the cylinder block and cylinder head (both Nemak-supplied castings), the crankshaft, the connecting rods, pistons, oil pump and oil pan,” he says.
High-strength cast crankshaft and forged rods replace the powdered-metal components used in the conventional port fuel-injected engine.
Plus, the EcoBoost uses full-floating piston pins and a DI piston dome, inner bore cooling and high-strength liners in a unique block that is bulked up at the bottom end. The valvetrain also benefits from friction reduction, Makowski says.
Among the primary design goals was achieving the oft-quoted mantra: “Power of a V-6, fuel efficiency of an I-4.” Beyond that were improved low-end response; refinements in noise, vibration and harshness characteristics; and decreased cost.
Improving performance and fuel economy, as well as catalyst warm-up for lower cold-start emissions, are goals for all auto makers, but that does not make it any less challenging.
“We integrated the exhaust manifold into the cylinder head with a compact gooseneck outlet that comes down into the turbo. That reduced the cost and improved the pulse energy to the turbo,” Makowski says.
But this design also results in increased heat in the cylinder head, so one goal was right-sizing the radiator and cooling systems.
“But you do get some benefits (from higher temperatures) because increased heat is not always a bad thing,” Makowski says. “For warm-up, you get to closed-loop fuel control much faster, and defrost times are reduced. The people in the vehicle program like that.”
Another issue inherent to the downsize-and-boost strategy is managing NVH, because a boosted I-4 can be noisier and less stable than the V-6 it replaces.
“We went to injector isolators between the direct-injection units and the cylinder head to minimize the ticking you often hear with DI engines, and we went to EPCBVs (Electronic Pneumatic Compressor Bypass Valves),” he says.
“Instead of the bypass valve just blowing off, we actuate it so when you get into a sudden decel or downshift, we can pop it open earlier to prevent turbo surge, which also helps NVH. We also went to a vacuum actuated wastegate. Depending on the mode the engine is in, if we don't need all the boost pressure we can use wastegate relief to reduce the pumping losses.”
The team focused intently on determining the proper size of the turbocharger. “You can put on a large turbocharger to achieve more power, but then you sacrifice your low-end because a large turbo has a lot of inertia and takes longer to spool up,” Makowski says.
“You don't want to give up part-pedal torque or launch responsiveness. Unless you're on a racetrack, you're driving torque, not horsepower. So we spent a lot of time with (the trade-off between) launch feel and power.”
Another major hurdle was the need to optimize cylinder mixing. “With the DI and the turbo, you're injecting high-pressure fuel directly into the chamber at 5,000-6,000 rpm on the high end, then idling it down to 700 rpm, and you have a lot of different conditions,” Makowski says.
“The whole mixing piece, both targeting the spray and controlling the timing, is extremely critical. There was a tremendous amount of CAE (computer-aided design) work up-front.
We used an optical cylinder to see what goes on in the chamber, and all that was followed up by a substantial amount of dyno testing and confirmations. At the end of the day, you've got to meet emissions, and the in-cylinder mixing drives fuel efficiency as well.”
Even though Ford claims 125 patents for EcoBoost, mostly for controls and control strategies, Makowski says the engine does not boast features that would be considered industry firsts. “But it’s the balance of attributes that allows us to put this into volume production and deliver the results that we’re getting.”
And the results are so good that Ford projects 90% of its vehicles will be available with an EcoBoost engine by 2013. With such a growth trajectory, engineers know improvement is paramount.
“In general, it comes down to (achieving an optimum balance of) power and fuel efficiency,” Makowski says. “As you downsize and boost, your ability to generate power along with fuel efficiency moves into the realm of new technologies.”
“New turbocharger technologies are probably a good bet in the future, and there are many opportunities to improve thermal efficiency and reduce friction and pumping losses. Also, NVH can't be degraded. We’re always being challenged with: ‘Give me more power; give me more fuel efficiency; and I want it quieter. Oh, and give that to me for lower cost.’”
As the EcoBoost I-4 demonstrates, those first three demands can be effectively met, at least for now. But the last one may prove increasingly difficult down the road.