2017 Story Behind 10 Best Engines
Minivans may be the U.S. market’s most practical – yet most under-appreciated – vehicle segment. is spicing things up by offering class-leading efficiency in an industry-first plug-in hybrid version of its Chrysler Pacifica minivan.
Its hybrid system teams a 220-hp, higher-compression, Atkinson-cycle version of FCA’s multi-award-winning Pentastar V-6 with two electric motors packaged inside its eFlite electrically variable transmission. A 16-kWh battery pack is mounted under the second-row floor where the conventional Pacifica’s Stow ’n Go seat tubs reside.
Unlike most other parallel hybrids with an eCVT, its (FCA-designed and built) eFlite transmission’s one-way clutch allows both motors to contribute torque to the front wheels during all-electric drive. “That innovation helps with electric drive efficiency to get our 84 mpg-e (2.8 L/100 km) and 33 miles (53 km) of all-electric range,” says FCA high-voltage electrification chief engineer John Gibson.
The primary drive electric motor generates 85 kW (114 hp) while the smaller (starter/generator) motor can contribute another 63 kW (84 hp) to drive the front wheels during all-electric operation up to 75 mph (121 km/h). In charge-sustaining mode, when the larger motor assists the engine, total system output is 260 hp and 235 lb.-ft. (319 Nm) of torque, more than adequate for the 4,987-lb. (2,262-kg) plug-in minivan.
Gibson says one of his team’s toughest challenges was developing the hybrid’s control systems. “One primary objective was integrating the controls of the internal-combustion engine, the motors and the battery to make it so seamless and smooth you can’t tell when the engine starts and when it stops.”
Another hurdle was making it as efficient as possible at all times under all conditions, continuously managing the battery and the torque from the engine and motors, “so our customers don’t have to think about selecting a drive mode to use the least amount of fuel because we do it automatically,” Gibson says.
“We set some very stringent efficiency targets, including 80 mpg-e (2.9 L/100 km) EPA city, and we’re very proud of the team’s hard work that enabled us to exceed that target,” he says. “In making it seamless and quiet, sometimes you have to weigh the impact on efficiency. I think we achieved a very good balance of drivability and seamless operation with very good efficiency.”
Gibson adds that segment-leading fuel economy even after the battery is depleted proved to be as much of a challenge to achieve as the system’s all-electric efficiency.
“We’re really happy with our 32 mpg (7.4 L/100 km) EPA combined charge-sustaining fuel economy,” Gibson says. “We use the electric drive even during charge sustaining, so our eFlite transmission with the one-way clutch is a key enabler not only in all-electric but also in charge-sustaining mode.” It helps the ’17 Pacifica’s drag coefficient is a surprisingly slick 0.30.
“Our judges awarded the Pacifica Hybrid high marks for the vehicle’s seamless drive quality as well as its technological advancement as the first mass-market electrified minivan in North America,” writes WardsAuto editor Bob Gritzinger.
“And when the 3.6L Atkinson-cycle V-6 did kick in, fuel economy still ran above 30 mpg (7.8 L/100 km) in our judges’ real-world, around-town driving, and topped 40 mpg (5.9 L/100 km) in one instance.”
By comparison, the conventional Pacifica is rated at 18/28 mpg (13-8.4 L/100 km) city/highway and 22 mpg (10.7 L/100 km) combined.
The Pacifica Hybrid accomplishes this while maintaining the passenger and cargo room of a minivan as well as the vehicle’s comfortable ride and steady handling, Gritzinger adds.
Pentastar V-6 Plays Key Role
Of course the modified V-6 also plays a key role in the system’s overall efficiency. “Electric drive is our first option,” Gibson says, “but when we need additional power or we’re out of battery, we seamlessly transition into hybrid mode and use the engine as needed. This type of system with an electrically variable transmission allows you to independently control engine speed and torque.
And with that flexibility, because we knew where we were going to operate it, we optimized the compression ratio and valve events to make it most efficient in those rpm ranges. The software is the challenge in making everything seamless and squeezing out every last bit of efficiency, but you also need the base component efficiencies.”
Not only was the eFlite transmission internally designed and developed, Gibson says FCA also developed and integrated all of the hybrid system’s controls, while the 16-kWh lithium ion battery pack was designed and developed by LG Chem in partnership with his team.
“The engineering of the pack was done here in Troy, Michigan and we had a very close relationship with them during its development,” he says. “They designed it to our specifications and worked with us to deliver those requirements, and they are manufacturing the battery in a plant here in Holland, Michigan. It’s been a very good working relationship.”
While the ICE Atkinson cycle enhances efficiency, it somewhat degrades performance, creating the ever-present issue of balancing output and economy.
“We sized our electric drive system to be perfectly in tune with how much power we have out of the Pentastar engine,” Gibson says. “Our Atkinson-cycle version does not deliver as much power as the standard Pentastar, but the combined system output is 260 hp, which is plenty for our customers, and the immediacy of the electric drive torque makes the vehicle very responsive in acceleration. The Atkinson cycle is a great trade-off with electrified vehicles in terms of using the electric drive to supplement the engine.”
Is the torque contribution of the electric motors the same regardless of state of charge? “Yes. In terms of available electric power and how we do peak system power management, the vehicle performance is essentially the same at full state of charge as with a depleted battery.”
However, despite all the team’s accomplishments, there is room for improvement, Gibson says.
“We are always looking for how to make it better. The history of electrified vehicles demonstrates that both performance and fuel efficiency continue to improve generation over generation.”
And, Gibson says the propulsion system can be upsized or downsized for use in other FCA vehicles. “We have designed it to be flexible to work in a broad spectrum of vehicle sizes.”