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Twin turbo V6 engines may have been around for a long time - think Nissan’s 300ZX VG30DETT engine – but for Ford in the US, they represent a radical rethinking in engine design for power and economy. Here’s the detail on the latest engine to join Ford’s stable – and the reasons Ford has built it.
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EcoBoost is a key Ford Motor Company initiative to deliver significant advancements in fuel economy – up to 20 percent – without sacrificing the performance customers want. The 3.5-litre EcoBoost engine delivers 365 horsepower and 350 lb.-ft. of torque across a broad rpm range, giving the power of a normally aspirated 4.6-litre V8 while, according to Ford, enjoying V6 fuel efficiency.
The 3.5-litre EcoBoost V6 is the first in a wave of EcoBoost engines coming from Ford. By 2013, more than 90 percent of Ford’s North American line-up will be available with EcoBoost.
Base Engine
The base engine architecture comes from the Duratec 3.5-litre V6. To handle the increased torque that EcoBoost delivers, upgrades were made to some of the components, including the cylinder block, crankshaft, connecting rods, pistons (note the unusual crown shape) and exhaust valves.
“The beauty of EcoBoost is that it enables us to downsize
[over a V8]
for fuel efficiency, yet boost for power,” said Derrick Kuzak, Ford’s group vice president of Global Product Development. “We’re able to decrease the size of the available engine – such as installing a V6 versus a V8 – yet boost the power using turbocharging to deliver similar power and torque of that larger engine.”
Turbos
Used are two Honeywell GT15 turbochargers with water-cooled bearings. They operate in parallel, spinning at approximately 170,000 rpm and developing up to 12 psi boost. They are rated for a 150,000-mile, 10-year life.
“We’ve tested the turbochargers at a much-higher duty cycle than a customer would ever experience,” said Keith Plagens, turbo systems engineer.
“Our whole goal from the beginning was to make the operation of the turbochargers seamless, so the customer wouldn’t even know they were there.”
The simultaneous turbocharger operation paired with direct fuel injection system helps to virtually eliminate turbo lag.
The dual-turbocharger setup has several advantages over single turbocharger systems, including:
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The turbochargers are smaller, resulting in more-compact stainless steel fabricated exhaust manifolds, which don’t radiate as much heat
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Turbochargers are packaged adjacent to the cylinder block and have improved mounting providing lower NVH (noise, vibration, harshness)
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The dual turbochargers spool up quicker, allowing the 3.5-litre EcoBoost V6 engine to reach peak torque faster
“We control the boost to make sure that customers don’t recognize when the boost is building,” said Brett Hinds, EcoBoost design manager. “As the turbochargers spool up, the electronic control system takes over. Our active wastegate control along with the
[electronically actuated]
throttle controls the boost and torque levels very precisely and the customer perceives a continuous delivery of torque.”
To validate their water-cooled turbo design choice, Ford engineers put EcoBoost through a special turbocharger test.
The test ran EcoBoost at maximum boost flat out for a 10-minute period. Then the engine and all cooling were abruptly shut down and the turbo was left to “bake” after this high-speed operation. This process was then repeated 1,500 times without an oil change. After the 1,500 cycles, the turbos were cut open for detailed technical examination and proved to be fine.
“We’ve attained things here the customer would never be able to do in their vehicle,” Plagens said. “Ten minutes of peak power (355 hp, 350 foot-pounds of torque) is something that’s probably only achievable in a vehicle for fractions of a minute, 10 seconds maybe in the extreme. We run it for 10 minutes many, many times over, and that’s far, far more harsh and severe than a vehicle test would be.”
EcoBoost also endured Ford’s standard engine durability test signoff. Back in the dynamometer lab, the 3.5-litre EcoBoost V6 went back up to full revs – and maximum turbo boost – for a real endurance test. This time it stayed at full throttle for 362 hours. That’s like running the 24 Hours of Daytona for more than 15 days straight.
Other tests subjected EcoBoost to a gruelling range of operating temperatures.
“We run all of our durability testing at the maximum temperature,” Plagens said. “For the turbos, the test is 150 hours long. Every 10 minutes the test alternates between peak power at max exhaust temperature and completely cold motoring. The goal is to verify that the turbochargers can withstand extreme thermal cycling without affecting their performance. It’s pretty brutal and extreme but it’s important to prove out durability.”
The engine uses that same grade of 5W20 engine oil specified by Ford for other gasoline engines, and oil changes are scheduled at the same 7,500-mile intervals, too.
“Ford customers can be sure that their new EcoBoost engine requires no special treatment for its reliable operation,” Shelby said. “EcoBoost owners can pull in their driveways and switch off just like any other engine, and there’s no special oil or shorter oil-change intervals.”
Direct Fuel Injection
Direct fuel injection is used.
Each bank of cylinders in the V6 EcoBoost engine has a high-pressure fuel rail that feeds the individual injectors. A fuel rail pressure sensor on each rail helps the vehicle powertrain control module precisely control the fuel pressure. A cam-driven high-pressure fuel pump feeds the fuel injectors at pressures ranging from 200 to 2,175 psi, depending on customer driving.
“By bringing the fuel injector right into the combustion chamber, there’s no delay from the time you inject the fuel to when it’s used by the engine,” said Hinds.
When the fuel is injected into the cylinder, it evaporates and cools the air that’s been inducted into the cylinder.
“Another benefit of our direct injection method is that it cools the air right where you’re going to burn it,” Hinds said. “This action both improves the breathing of the engine and minimizes knocking.”
The direct injection of fuel into the cylinder also helps provide a well-mixed air-fuel charge, increasing engine efficiency.
The Bosch high-pressure fuel injectors use internal solenoids to switch on and off the flow of fuel extremely precisely. Fuel flows through six tiny outlets – like pinholes – in each injector, and each spray is positioned to provide benefits in fuel economy and emissions.
Electronic control system varies the timing and intensity of the fuel delivery according to engine operating conditions.
“Because the fuel is directly introduced into the combustion chamber, you don’t get fuel wetting the combustion wall like with port fuel injection, you don’t saturate the ports and you don’t get droplets that might recombine and add to saturation,” Hinds said.
“By injecting fuel directly into the combustion chamber and under high pressure, the fuel can be directed to exactly where we want it to be for a given combustion cycle.”
The spray pattern for the fuel was optimized after extensive modelling work, with the spray angle key to the process.
“The better combustion process is a big advantage of direct injection,” Hinds said. “In a port fuel system, at key-off it’s possible to have fuel on the walls of the intake port, which migrates to the top of the valve and puddles. So when you key-on, you get that emissions spike. Direct injection is much cleaner from that standpoint.”
“By injecting the fuel directly into the combustion chamber and under high pressure, the fuel is sent exactly where we want it to be for a given combustion cycle,” said Joseph Basmaji, direct injection fuel system technical specialist. “This aids burning of fuel more efficiently and effectively.”
Transmission
Mated to the 3.5-litre EcoBoost V6 engine is the 6-speed 6F-55 SelectShift automatic transmission, which is dedicated to the twin-turbocharger engine.
The 6F-55 transmission was developed from the 6F-50 transmission to specifically respond to the increased torque demands of the EcoBoost V6 engine. Upgrades were made to the transmission’s friction material in response to the higher shift energies, and a new torque converter has been optimized for performance and fuel economy.
Additionally, the 6F-55 transmission operates more efficiently. The transmission team was able to reduce the fluid level in the transmission, which in turn reduced weight and drag torque on the system. Upgrades to the transmission’s thermal valve mean the system warms up quicker, reducing gear-spin losses.
“We’ve upgraded the gear sets to handle the increased torque,” said Joe Baum, powertrain team leader. “We’ve also adjusted the final drive ratio and matched the gear ratios to provide the optimum performance and fuel economy.
“Our final drive ratio is 2.73. With a lower final drive ratio, the engine spins lower at highway speeds, which helps save fuel. And with all the torque, the Ford Flex still delivers good low-speed launch performance.”
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