Ford 2.5L I-4 Hybrid: Unprecedented Efficiency, Refinement

The Ward’s 10 Best Engines competition has recognized outstanding powertrain development for 16 years. This month, Ward’s examines the design philosophy behind Ford’s hybrid-electric powertrain.

Few would dispute Toyota Motor Corp. is the established industry leader in hybrid-electric vehicles, at least in terms of sales volume, yet Ford Motor Co. now is emerging as a hybrid-technology leader in both energy efficiency and customer-pleasing refinement.

Ford’s leadership begins with the numbers. Ward’s 10 Best Engines ’10 Ford Fusion Hybrid delivers an eye-opening 41/36 mpg (5.7-6.5 L /100 km) city/highway, in Environmental Protection Agency testing, compared with 33/34 (7.1-6.9 L/100 km) for the similar-size Toyota Camry Hybrid and 35/33 mpg (6.7-7 L/100 km) for the Nissan Altima Hybrid, which uses Toyota technology coupled to its own 2.5L 4-cyl. engine.

And it continues to have a superb level of refinement for an HEV, all of which have inherent noise, vibration and harshness issues because of the complex interaction between the gas engine and electric motors.

Ford’s original Escape Hybrid was powered by what many erroneously believed was a clone of Toyota’s Hybrid Synergy Drive system. It drove fairly well and offered surprising fuel economy for a compact cross/utility vehicle. But it commanded little attention and sold in modest numbers.

However, Ford’s truly impressive Gen II hybrid system in the substantially upgraded ’10 Fusion midsize sedan is a whole new ball game.

Its new 156-hp, 136 lb.-ft. (184 Nm) 2.5L DOHC Atkinson-cycle aluminum I-4 teams with a 106-hp electric drive motor for a surprisingly satisfying combined peak output of 191 hp. It also can drive up to 47 mph (76 km/h) solely under electric power.

Fusion Hybrid is efficient and fun to drive.

That’s useful when scouring a parking lot for a space, creeping along in a traffic jam or just impressing passengers.

Ford’s recently updated ’10 Escape Hybrid offers a “Gen 1.5” system that shares the Fusion’s 2.5L iVCT (intelligent variable cam timing) engine, system controls, higher-power battery cells and electric compressor.

What it doesn’t yet have are the Fusion Hybrid’s next-generation transaxle (with downsized traction motor and generator); its smaller, lighter nickel-metal-hydride battery pack; or its boost converter, which temporarily can raise voltage to drive the motor by up to 160%.

Besides sharing its 2-motor torque-split operating concept, what does Ford’s Gen II system have in common with Toyota’s Synergy Drive? Virtually nothing, says Sherif Marakby, director-electrification programs and engineering, who probably is tired of that question.

“Our system is not similar in any way to Toyota’s,” he says. “The hardware and execution of the software are unique. We do all the controls and software and all the calibration in-house. Ford has over 200 patents on the control system just on this architecture.”

2.5L I-4 offers more low-end power.

“We spent a lot of time sizing and optimizing the design of the components, including the battery, the motors, the inverters that drive the motors and the power flow for highest efficiency.”

In normal operation with a fully charged battery, the system runs at an optimal 400 volts, and the new boost converter increases the voltage only as needed.

“Depending on what the driver is demanding, we try to run as much as possible at the most efficient points of the electrical components,” Marakby says.

We also look at the BSFC (brake specific fuel consumption) map of the engine and run it at its optimal point, and we balance all that through the control system to manage the energy.”

“Certainly, everyone is trying to optimize their systems. But the Fusion Hybrid has superior fuel economy vs. the competition, because of how we execute the system and optimize the energy across components, not just for each component.”

Dean Tomazic, vice president-Engine Performance and Emissions Div. at FEV Inc., agrees. He says the importance of controls, operating strategy and software programming play a pivotal role in the performance of HEVs and creating the subtle nuances that end up impressing drivers.

It is a battle that will continue to be waged as HEVs grow ever more complex, Tomazic says. “Controls and operating strategy will evolve continuously for a long, long time.”

Marakby says the other major Gen II engineering priority was improving the general refinement of the powertrain.

“Our vision is the best fuel economy and the most refined, meaning very smooth operation. When the engine stops and starts as often as it does in a hybrid, it should be completely transparent to most customers.”

One key contributor to that is the new engine’s intelligent variable cam timing, which reduces airflow on start-up and shutdown while improving catalyst efficiency. Another is the Gen II’s advanced control system.

However, muting or eliminating the multitude of unusual sounds that a complicated HEV powertrain can emit during normal operation is a challenge.

“One thing we learned on the original Escape Hybrid was that the customer can deal with predicted noises,” he says. “If you’re accelerating, you expect to hear the engine. But customers do not like noises that are not expected.”

So Ford engineers worked hard on unwanted sounds from the traction motor, motor-driven pumps and the brake system’s vacuum pump.

“There are a lot of frequencies that come out of the motor, especially when you’re slowing or braking, so we spent a lot of time developing the software and controls of the traction motor to avoid certain frequencies during some maneuvers,” Marakby says.

Ford engineers also reduced the system’s cost by more than 30%, largely through component integration and battery downsizing. “Our goals were lighter, smaller and lower cost, plus efficiency, and we were able to deliver on all of those attributes on most components.”

Yet, there still is lots of room for improvement. Ford’s Gen III HEV will be better and more refined and more efficient, and it will cost less, Marakby says. One reason for his confidence is lithium-ion battery technology.

“I think as an industry, our future is lithium-ion,” he says. “We are spending a lot of time characterizing the chemistry and making sure we’re operating very efficiently.”

The plan is to launch battery-electrics with Li-ion in the next year, and the next-generation HEVs and plug-in HEV will launch by 2012 with Li-ion battery packs.

“(Li-ion) is smaller, lighter and more efficient. It’s three times the voltage per cell vs. today’s NiMH, so you’re generally using a third of the cells to get the same voltage. We’re working on the cost, and it’s looking very promising,” Marakby says.

In addition, Ford’s hybrid engineers are going through a component size, weight and cost and efficiency optimization effort similar to what they did for Gen II.

“A lot of these components are running at 94%-96% efficiency,” Marakby says, “And we’re taking the next steps to go out a few more percent. You’ll definitely see better fuel economy as we go forward.”

FEVs Tomaczik says the further electrification of engine accessories such as the water pump is another likely step.

Even so, making HEV technology more affordable remains a herculean task, Marakby admits.

“Most manufacturers price hybrids $2,000-$3,000 above base vehicles with comparable equipment, but we are not at the point yet of being able to get the cost down (to that margin),” Marakby says. “That’s why you don’t see 50% market share for hybrids out there.”

– with Drew Winter