Integrating a Plug-In Hybrid Jeep

May 1, 2022

Lindsay Brooke

At no other time in the auto industry’s history has the role of vehicle integration and synthesis been so important. The growth of electronic content, the melding of mechanical and electrical engineering and the increased focus on electrified propulsion have made integration/synthesis teams vital to ensuring that design spec and requirements are maintained through prototypes, testing, and validation, in order to meet market standards and exceed customer expectations.

Eunjoo Hopkins (right) is vehicle synthesis manager on the 2022 Jeep Grand Cherokee 4xe plug-in hybrid (called “4-by-e” by Stellantis engineers). She joined the former FiatChrysler in 2009 as a Powertrain engineer and only recently moved over to vehicle integration. “I’ve worked in propulsion systems for most of my career here thus far, including the [Chrysler] Pacifica Hybrid,” she told SAE Media during the Grand Cherokee 4xe media launch in Texas. “I moved into integration/synthesis because I wanted to experience the other aspects of vehicle development.”

Integration, she explained, “is all about what we call ‘the sciences’ – aerodynamics, safety, NVH, vehicle dynamics. We have to make sure we meet the ‘science’ goals established for the program, all the way back to component design,” she noted. For the Grand Cherokee 4-by-e, that includes metrics such as foundation braking feel as well as regen braking. Calibration falls under Powertrain, however. “If there is a metric we don’t meet, we go back and redesign the component,” Hopkins asserted. “We’re also responsible for holding ride-and-drives with our executives to get their inputs and buy-in to make sure our products meet customer expectations.” Highlights of our conversation with Hopkins follow.

Is most of the Grand Cherokee 4xe’s PHEV powertrain carried over from the Jeep Wrangler 4xe?

Yes, but with more refinements. Being able to pick up the propulsion system from Wrangler allowed us to move the program along much more quickly. The challenge, however, was the different electrical architectures of the two vehicles. The Wrangler’s architecture is very different from the WL [internal code for the new Grand Cherokee] in how it does ‘wake up’ and ‘sleep,’ for example. That’s where a lot of complication came in for us, in integrating [the hybrid system] with the vehicle architecture. Grand Cherokee and Grand Wagoneer have all-new electrical architectures, as Tom Seel [Grand Cherokee vehicle line engineer] has noted.

The PHEV system combines P1 and P2 electric machine positions. What do you call that combination?

We call it a ‘P1-P2.’ Integrating the hybrid transmission into the Grand Cherokee, seamlessly, is where our learnings from Wrangler came in. To make its engagement and disengagement smooth in all operating modes, including engine-on/engine-off and at launch, required a lot of hard work in terms of control-algorithms and calibration. The vehicle has a separate transmission controller, which ‘plays nice’ with the supervisory controller.

A key to any electrified Jeep is thorough and robust sealing of the battery, controllers and the high-voltage harness from water intrusion. Did sealing the Grand Cherokee pose challenges?

We used industry standard specifications for sealing. We didn’t do anything special. We made sure that we validated those requirements at the VP [prototype] stage. When we hand-build our prototype vehicles, we use as much of the actual factory processes as possible. Before we put this vehicle through our first water fording test, we contacted all the DREs [design release engineers] to make sure the parts they supplied truly did pass the component-level testing.

The WL team drove the Grand Cherokee 4xe over the 22-mile Rubicon Trail on electric power only. How much did regen braking play a role in getting through that journey?

That’s interesting. Doing the Rubicon Trail is a low-speed event; not a lot of power is used. When you tip out of the throttle, you’re using the electric machine to absorb that energy. On that run, we typically used the forward motion of the vehicle and the driver’s foot to modulate vehicle speed. In the end I believe we still had some battery energy left.

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