Cummins researchers will optimize the powertrain by selecting the engine with the best architecture to use as an electric commercial vehicle range extender, using the engine to manage the charge level of the all-electric drive battery pack. The range extender will be integrated, using advanced vehicle controls, with the electrified powertrain and other applicable technologies.

The second project, in partnership with TM4, STL (Société de transport de Laval, the public transit system in the city of Laval, Québec) and IVI (Innovative Vehicle Institute, a non-profit research center), is developing two different models of a plug-in hybrid bus, using different battery chemistries and charging schemes.) The plan with this project, said Parker, is to let the two different chemistries—LTO and NMC—compete head to head for more than a year, and see which one wins.

LTO is a power battery, handles high C rates and has good durability, Parker said. NMC has double the energy capacity and is attractive from a cost point of view, but carries risk in performance and durability. Both chemistries meet the performance targets.

Parker drew an analogy to this approach with Cummins’ history. In 1934, Clessie Cummins brought two cars to the Indianapolis 500—the two-stroke Nº 5 and the four-stroke Nº 6—to test effectiveness of 2-cycle versus 4-cycle diesel engine designs for durability and efficiency. After the race and the post-race tear-down, Cummins settled on 4-cycle engines.

One bus will be LTO, the other bus will be NMC. We’ll be watching these chemistries and learning from them. We might say both are needed for the market, or we might say that one is a clear winner.

—Gary Parker

The buses will use an on-board 20 kW charger for off-duty charging; for an external in-route fast-charger, the team will use a 450 kW charger.

For range-extending engines, Parker said, Cummins looked at the bottom half of its portfolio: engines from 2.8 liters up to the 6.7-liters. For both the DOE project and the Laval bus project, Cummins is opting to develop its 4.5-liter engine as the genset. The team is considering fuel-flexibility as well (e.g.,CNG).

In the North American transit market, the 8.9 liter is the major engine in the space, Parker noted; Cummins is basically cutting the displacement requirement in half with the PHEV configuration.

The duty-cycle requirements for the plug-in buses are rigorous:

• 13-20 hour days
• Route cycle of 11-66 minutes
• Fast charge time of 5 minutes
• Daily mileage of 135-351 miles
• % idle time of 24-60%
• Daily stops: 957-1,131
• Daily traction energy: 580-890 kWh

The combination of regeneration, grid charging and genset power will fulfill driver demand, Parker said.

Cummins is well positioned to take electromobility across markets. The PHEV range extender will be a robust solution in certain markets—we certainly see that in bus. Truck and bus have a different set of customers, different expectations; we’ll be trying to understand that better. Building the right charging infrastructure will be important.

—Gary Parker