Ward’s 10 Best Engines competition has recognized outstanding powertrains for 21 years. This installment of the 2015 Behind the 10 Best Engines series looks at the development of Ford’s 3-cyl. EcoBoost.
Pick up a 1.0L water bottle. On a hot day, you can probably drink it down in three big gulps, each one the size of one of this remarkable little engine’s three cylinders.
We wrote earlier about the BMW/Mini 1.5L I-3, a fellow 2015 Ward’s 10 Best Engines winner, which generates a satisfying 134 hp, or 89 hp per liter.
This 1.0L engine, which motivates Ford’s U.S. Fiesta SE and 20% of the cars it sells in Europe, at two-thirds that size, is good for 123 hp. Even the mathematically challenged can see that's a whopping 123 hp/L, right up there with the Bugatti Veyron in specific output.
And this is its second straight Ward’s 10 Best Engines trophy. “Ford's gutsy 1.0L EcoBoost won the judges over for a second year with its 15 seconds of grin-inducing 148 lb-ft. (200 Nm) of overboost, throaty exhaust note and excellent fuel economy,” WardsAuto editor Drew Winter wrote, adding that its non-temporary-overboost torque rating is 125 lb.ft. (169 Nm). The 5-speed manual Fiesta SE in which they tested it also was determined to be “a hoot to drive.”
“No matter the price of our test vehicle, the 1.0L EcoBoost just isn’t an entry-level engine,” he enthused. “It doesn’t drive like one, it doesn’t sound like one, and there is nothing cheap about its engineering...it stands up on its hind legs and barks. It loves to rev.”
U.S. EPA-rated fuel economy is 31/43 mpg (7.6-5.5 L/100 km) city/highway, 36 mpg (6.5 L/100 km) combined. WardsAuto editors averaged 35.3 mpg (6.7 L/100 km) over 351 miles (565 km) of spirited driving.
“It's hard to get below 35 mpg (6.7L/100 km) in any driving situation,” says one juror.
To qualify as a Ford EcoBoost engine, it shares three key technologies: direct injection, turbocharging and dual variable-valve timing, which Ford calls twin Variable Cam Timing (VCT). The Bosch high-pressure DI, capable of multiple injections per stroke through 6-hole solenoid injectors, enables more precise fuel dosing, which cools the air/fuel mixture prior to combustion to allow a higher compression ratio.
The very small, low-inertia, high-speed Continental turbocharger produces 90% of the engine’s peak torque from as low as 1,350 rpm with minimal lag. The twin VCT provides excellent scavenging and higher peak output while improving efficiency.
Ford says this 999cc I-3 not only is its smallest EcoBoost engine but also its most advanced. An ultra-low friction design with an integrated exhaust manifold, it has split cooling circuits, a cam-drive belt that runs internally through the oil sump and an intentionally unbalanced flywheel and crankshaft pulley. The offset is designed to counteract the 3-cyl. engine’s inherent pitch and yaw and eliminate the need for an efficiency-robbing balance shaft.
A “smart” alternator increases recharge load under deceleration. It has a cast-iron block for strength, stiffness and NVH reasons.
Stoichiometric Air-Fuel Ratio a Priority
Besides minimizing friction, a key design priority was being able to run as closely as possible to a stoichiometric air-fuel ratio, the theoretically ideal lean mixture that Ford's British engine team refers to as Lambda One.
“Lambda is the ratio of how close to stoichiometric your engine is running,” says 1.0L engine system supervisor John Moffat. “If you run at less than one, you’re running rich. We generally want it as close to stoichiometric as possible, but unfortunately at very high loads and engine speeds, you have to run a bit richer to protect the engine hardware.
“Very hot exhaust gases can overheat the exhaust manifold or damage the catalyst, so a lot of gas engines inject extra fuel to reduce exhaust manifold temperatures and cool the catalyst – usually for a very small window of time – in those conditions. This is called over-fueling.”
The team set out to reduce that over-fueling window at high load, and one way was to cool the exhaust gases directly using a water jacket. But casting the exhaust manifold inside the cylinder head's cooling jacket presented a major challenge, Moffat says, “Because the heat flux from the exhaust can be huge. We had to go through a large number of iterations and tests to make sure the coolant flow was sufficient for cooling but not so large as to add a lot of weight or coolant volume.”
The 1.0L also has two distinct cooling circuits, one for the top end and turbo and one for the block. Being able to separately cool the top circuit, including the exhaust manifold, to enable running close to stoichiometric across the entire rev range benefits emissions and fuel economy. And because it is shared with the heater core, it warms up the car quickly. The second circuit warms the block to bring up the oil temperature and reduce friction more quickly.
“Another thing we wanted to do was reduce the overhang and the whining you get from belts,” Moffat says.
“The primary belt that goes from the crank up to the camshafts can be a problem to package in small engines, and it usually makes a lot of noise. So we decided to run the belt internally, from the sump up to the camshafts. That meant it would run through the oil, which we didn't think had been done before. “We did a lot of research to make sure it could run in oil in that temperature range and wouldn't swell up over time. That gave us a neat package with an NVH bonus because any belt noise is absorbed in the oil, which also lubricates the belt and reduces friction.”
Did any really tough challenges keep him awake at night?
“Just getting the power density right,” Moffat says.
“For a long period of time, we felt that perhaps we had gone too far in power density. This is one of the most power-dense engines in the world, so we were nervous that we had downsized too far, that we might be putting too much heat flux through it and too much power into the bearings, crankshaft and pistons for such a small engine. We needed that performance, and we could have done it with a 1.2L, but the challenge was to get it below 1.0L. That was the challenge we accepted and the one that gave us the most problems.”
As lively and efficient as this mighty-mite I-3 is today, Moffat says there always is room for improvement.
“We are working to make the power output higher. We are on sale in Europe with a 140-hp version, and the next generation for the U.S. will incorporate new technologies to improve fuel economy. It’s already a good low-friction, low-fuel-consumption engine, but we’ve been given the challenge to make it even more efficient, and we have some new technologies that will help us get there.”
