Carmakers regularly tweak their powertrains to boost fuel efficiency or improve performance and drivability.
Changes to EPA test cycles for 2017 mean that the agency's fuel-economy ratings for many new cars have fallen slightly.
Knowing that, and having learned more about how its various hybrid models were used in the real world, Ford set out to modify its Fusion Hybrid and Fusion Energi plug-in hybrid models for 2017.
DON'T MISS: 2017 Ford Fusion Energi electric range rises to 22 miles
The results have been released in stages, with the company first discussing the improved drivability last January.
Then, in May, it released test results for the 2017 Ford Fusion Energi, whose range rose to 22 miles, with 21 miles of that delivered continuously on the EPA's test cycles.
The 2016 figures were 20 and 19 miles, respectively. The full stats for the two cars can be compared on the EPA's FuelEconomy.gov website.
2017 Ford Fusion Energi
Efficiency ratings for the Fusion Energi rose too: it's now rated at 42 mpg combined in hybrid mode, when battery energy has been depleted, and 97 MPGe when running entirely on electricity. The 2016 ratings were 38 mpg combined and 88 MPGe.
All 2017 Fusions received a mild refresh that included a new front end that reduced aerodynamic drag.
But to understand in detail what Ford did specifically to its hybrid powertrain for both Fusion versions, we spoke to engineer Ben Nault earlier this month.
GET MORE DETAIL: 2017 Ford Fusion Hybrid, Energi: Software Tweaks For Drivability Improvements
Nault is an engineering manager for feature calibration and systems analysis in hybrid powertrains. He provided more details on the several different changes Ford made in its Fusions, including some that applied both to conventional and hybrid versions.
First, brake drag was reduced with a new caliper design that kept the pad slightly further away from the disc. This alone produced a 0.1-mpg improvement in the EPA rating, Nault said.
Second, while the look of the Fusion has changed relatively little, the aerodynamic changes included not only subtle reshaping of the front end but also improved sealing of the hood to reduce turbulence over and through the seam between hood and other panels.
2017 Ford Fusion
Third, Nault noted that Fusion engines starting with the 2015 model year had a different grade of oil specified to reduce internal drag. The previous 5W-20 was changed to 0W-20 (a blend that older auto hands may not even have known about).
Fourth, he noted that thinner steel plates were used in the hybrid system's motors, producing the necessary electric field from lighter components that cut the weight of the hybrid system.
Fifth and most significantly, Nault discussed the work of his calibration team in refining the huge set of controls that oversee every aspect of engine operation, electric motor and battery operation, and the interaction of the two.
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The control logic issues commands based on continuous analysis of dozens of parameters to determine the most efficient way to operate the elements of the powertrain under any given set of circumstances when the car is operating in hybrid mode.
This is a separate set of logic from the two different systems that govern operation of the electric systems only when the hybrid and plug-in hybrid Fusions are operating solely on battery power, he noted.
The goal is to keep the engine operating at its most efficient level while supplying whatever power is needed to meet the driver's commands through a combination of torque from the engine and electric motor.
2017 Ford Fusion Energi
The optimization effort began, Nault said, through analysis of data captured from "flight recorders" installed in vehicles operated by Ford employee volunteers.
Those logging devices captured "second by second data of the powertrain operation whenever the vehicle was started," largely from C-Max hybrids (which went on sale a few months before Fusion hybrids).
"That data provided the more detailed powertrain control and fuel economy information needed for better analysis of the effects of varying drive routes, environmental conditions, and customer use on powertrain operation and efficiency."
The team's revisions focused largely on shorter drive cycles, since the emissions of any engine are greatest—and its operating efficiency is lowest—when it has just started, before it warms up to full operating temperature.
"The occurrence of short trips was also observed in aggregate data sets obtained through research and MyFord Mobile databases," Nault continued. That data covered all cars, not just hybrids or Ford hybrids.
2017 Ford Fusion
All that data combined led the team to look at the current set of calibrations and embark on the effort to refine and improve them, with the goal of boosting fuel efficiency on the shortest trips.
The team worked to manage the engine warming-up process better and more quickly to boost efficiency, with dozens of incremental changes to minor operating parameters to get the engine warmed up more quickly and into its most efficient operating modes.
The result, he said, is an improvement of 1 percent to 4 percent in efficiency, "depending on the drive-route length and conditions."
And while that may have only a minor effect overall on EPA ratings, he notes, those hybrid and plug-in hybrid drivers who use their cars on lots of individual short trips could well see a "pretty substantial" improvement in their fuel economy.