The Ward’s 10 Best Engines competition has recognized outstanding powertrain development for 15 years. In this latest installment of our 2009 series, Ward’s highlights the design philosophy behind Ford’s second-generation hybrid-electric powertrain. Call it the “wow” factor, or better yet, the “woohoo” factor: the thrill of driving almost 40 mph (64 km/h) under purely electric power.
It’s one of several key features, along with spectacular real-world fuel economy and noise, vibration and harshness improvements, that have transformed Ford Motor Co.’s hybrid-electric propulsion system in its second-generation Escape Hybrid from a “me too” in the marketplace to a Ward’s 10 Best Engines award winner.
“Ford was regarded more as a follower, whereas the new generation of the Escape and Fusion (HEVs) definitely are on the leading edge,” says Joachim Wolschendorf, FEV Inc. chief technical officer and vice president-Vehicle and Drivetrain Engineering Div. FEV is an independent powertrain research and development company.
The terms “hybrid” and “fun-to-drive” rarely find themselves in the same sentence, but Ford engineers did it by listening to their customers and then carefully optimizing key components and driving modes to deliver a new type of environmentally friendly driving experience. It replaces the old herky-jerky feel of the traditional HEV with something more akin to the pulse-and-glide driving pattern used by hyper-milers.
Since Ward’s tested the Escape Hybrid cross/utility vehicle late last year, Ford has introduced a hybrid version of the Fusion sedan, which uses the same powertrain but incorporates a number of significant improvements, including the ability to go faster under electric power, up to 47 mph (76 km/h).
With fuel economy of 34/31 mpg city/highway (6.9-7.5 L/100 km), the Ford Escape Hybrid is stunningly fuel efficient, and we easily exceeded those numbers during testing.
The Fusion Hybrid offers even better numbers, 41/36 mpg (5.7-6.5 L/100 km), and has demonstrated far higher efficiency in real-world testing (although a Ward’s test during one of Michigan’s coldest days yielded weaker results).
Because they are designed to be HEVs and not plug-in electrics, both the CUV and the sedan only can drive about one mile (1.6 km) at 40 mph or so under full electric power. But that’s plenty of time to deliver a unique and addictive driving experience, one that, unlike most of Ward’s 10 Best Engines, creates the urge to jam the throttle as little as possible.
Ford Hybrid Applications Manager Gil Portalatin says maximum fuel economy was the primary goal of the second-generation system, but customers definitely were asking for the ability to drive longer and faster under electric power. That strategy led engineers to take a page from the hyper-miler playbook, which stresses lots of coasting.
This tactic meant putting work not only into smoothing power transitions from gasoline to electric motors during acceleration, but also being able to seamlessly shut off the internal combustion engine as much as possible whenever the car is slowing down.
One of the keys to the HEV powertrain’s high real-world fuel economy is the fact the IC engine shuts down frequently during deceleration, FEV’s Wolschendorf says.
“If the engine is not running, you have massive fuel economy gains, and you should shut it off as much as possible, particularly during deceleration. That’s a big advantage of this calibration,” he says.
However, Wolschendorf warns, you have to make sure the driver is not alarmed or confused by the engine shutoff during deceleration. “Which means you need to do a pretty good job with your NVH optimization, so that the customer really doesn’t notice the engine shutting off or kicking in,” he says.
Part of the credit goes to Ford’s aggressive use of engine braking, instead of the foundation brakes, to initially – and smoothly – slow the vehicle.
“The driver is not confused by what is happening and does not even notice that the engine shuts off or the vehicle is decelerated by the electric motor, rather than by the brakes. Both aspects go hand-in-hand with what Ford has done with this vehicle,” Wolschendorf says. An added benefit is less brake-pad wear.
In fact, Ford engineers say optimization and refinement of each specific component, and the system as a whole, is the key to the new powertrain’s success.
Praveen Cherian, Fusion Hybrid systems manager, says engineers have removed 30% of the cost from the previous-generation system.
Plus, there have been significant enhancements even between the development of the Escape Hybrid and Fusion Hybrid.
Both use the same 2.5L DOHC I-4, but the transaxle on the Escape still is a first-generation model with software and control-strategy improvements. The new Fusion features the next-generation transaxle with a downsized traction motor and generator, plus the addition of a variable voltage controller, that allows engineers to over-boost the electric motor by up to 160%.
“They sit in the same casting, because we made them common to maximize efficiency, but the Fusion transaxle has unique refinements,” says Portalatin.
The new nickel-metal-hydride battery on the Fusion also has 17% fewer cells and is 23% lighter, because of new battery cell chemistry changes.
“We’re constantly looking at what more we can do for the efficiency of individual components,” says Cherian. The direct current converter on the Fusion, for instance, is smaller, lighter and has almost 14% more power output, he says.
Information processing capability has been enhanced as well. “We have so much information flowing through the system; we have smart climate-control strategies that are integrated into the overall stop-and-start of the engines.”
Cherian says the system will keep track of a passenger who wants the temperature at 75° F (24° C) in their zone, because such a high setting on a cold day means the engine will have to run longer to generate enough heat.
“If we know nobody is sitting in the passenger seat, we can ignore the setting and shut the engine down much earlier,” Cherian says.
While much of the story behind Ford’s latest-generation HEV propulsion system is about software and system optimization, it would be unfair not to mention Ford’s all-new 2.5L DOHC I-4, which replaces the less capable 2.3L I-4 in the first-generation HEV.
With intake variable camshaft timing, the new 4-cyl. delivers a broader power band and operates on the Atkinson combustion cycle (similar to most other hybrids), which improves efficiency up to 10% over conventional Otto-cycle configurations by keeping the intake valves open longer.
This reduces the engine’s pumping losses by allowing a small portion of the fuel/air charge to flow back into the intake.
Mechanical changes include new intake and exhaust manifolds; new intake camshaft; and higher-compression pistons (12.3:1) vs. the non-hybrid I-4 (9.7:1).
The improved IC engine played a key role in improving the NVH characteristics of the entire system, Portalatin says.
“It allowed us to vary the intake cams to maximize fuel economy and improve transitions from gas to electric and electric to gas, because we could do a better job of aligning the torque and getting (the gas and electric motors) in synch, so to speak. That was a big deal,” he says.
What does the future hold for this very futuristic powertrain?
Both Portalatin and Cherian say they are very pleased with today’s NiMH batteries, which are proving to last more than 300,000 miles (483,000 km) in taxi fleets in both New York and San Francisco, but they decline to discuss future product.
However, Ford has announced plans to use advanced lithium-ion batteries for an electric vehicle slated for the ’13 model year, as well as a future plug-in HEV. Many observers expect Ford eventually to shift its HEVs to li-ion as well.