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Integrating a plug-in hybrid Jeep

Integrating a plug-in hybrid Jeep

There is no other time in the history of the automotive industry that has played such an important role in the integration and assembly of vehicles. The growth of electronic content, integration of mechanical and electrical engineering, and increased focus on electric drives have made integration/tuning teams critical to ensuring that design specifications and requirements are maintained through prototyping, testing and validation to meet market standards and exceed customer expectations.

Eunjoo Hopkins (right) is the director of vehicle tuning for the 2022 Jeep Grand Cherokee plug-in hybrid (Stellantis engineers called it “4-by-e”). He joined FiatChrysler previously in 2009 as a powertrain engineer and recently moved into vehicle integration. “I’ve worked in propulsion systems for most of my career here so far, including [Chrysler’s] Pacifica Hybrid,” he told SAE Media at the launch of the Grand Cherokee 4xe Media in Texas. “I moved to integration/installation because I wanted to experience other aspects of car development.”

He explained that integration “is about what we call ‘science’ – aerodynamics, safety, NVH, vehicle dynamics. We have to make sure we meet the ‘science’ goals set for this program, right down to the design of the components.” For the Grand Cherokee 4- by-e, it includes metrics such as basic braking feel as well as regenerative braking. Calibration is included in the powertrain. “If there’s a metric we don’t meet, we go back and redesign the component,” says Hopkins. “We are also responsible for traveling with our executives to get their input and purchases to ensure our products meet customer expectations.” Here are some highlights from our conversation with Hopkins.

Was Most of the Grand Cherokee 4xe’s PHEV Powertrain Transferred From The Jeep Wrangler 4xe?

Yes, but with more improvements. Being able to pick up the Wrangler drivetrain allowed us to move the software more quickly. The challenge, however, is the different electrical engineering of the two vehicles. The Wrangler’s architecture is very different from the WL [a symbol of the new Grand Cherokee interior] in how it “wake” and “sleep”, for example. That’s where a lot of the complexity comes in for us, in integrating [the hybrid system] with the vehicle architecture. The Grand Cherokee and Grand Wagoneer have completely new electrical designs, says Tom Seal [Grand Cherokee line engineer].

The PHEV system combines P1 and P2 electric engine modes. What do you call this group?

We call it “P1-P2”. Incorporating a hybrid transmission into the Grand Cherokee, seamlessly, is where our learning from the Wrangler comes in. To make interaction and disconnection seamless across all operating modes, including engine on/off and at launch, a lot of hard work is required in terms of control and calibration algorithms. The car has a separate transmission control unit, which “plays well” with the supervisory control unit.

The key to any electrified Jeep is a comprehensive and robust sealing of the battery, controls, and high-voltage belt from water leaks. Did the closing of the Grand Cherokee present any challenges?
We use industry standard specifications for sealing. We didn’t do anything special. We made sure to validate these requirements at the VP [Prototype] stage. When we prototype cars manually, we use as much of our actual factory processes as possible. Before we tested this car for the first time, we called all the DRE [Design Launch Engineers] to make sure the parts they supply actually passed the component level test.

The WL team rode a Grand Cherokee 4xe across 22 miles of Rubicon Road on electric power alone. To what extent did regenerative braking play a role in getting through that journey?
That is interesting. Doing the Rubicon Trail is considered a low speed event; Not much energy is used. When you step on the gas, you use an electric engine to absorb that energy. In this run, we usually use the forward movement of the vehicle and the driver’s feet to regulate the speed of the vehicle. In the end, I think we still have some battery power left.