Cummins is more and more engaged in the development of plug-in hybrid powertrains these days.

On top of a medium-duty Class 6 vehicles project supported by the DOE, there is also another undertaking for heavy-duty vehicles - like Class 7 and 8 buses.

TM4 electric motors

TM4 electric motors

The latest project was hinted at by Gary Parker (who is the Director of Electromobility programs for Cummins, Inc.) at the SAE 2016 Range Extenders for Electric Vehicles Symposium - which is apparently a real thing.

Partners in the bus project are 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).

Including TM4 in the process means that the electric motor/inverter components are already set and done. On the battery side, there are two options on the table - LTO and NMC chemistries - LTO for fast charging (lower range), and NMC for longer range ( but slower charging). The idea is to use two prototypes for over a year, and then decide which approach is better.

Parker said:

"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."

For charging there will be two options - a 20 kW on-board charger, and an external in-route fast-charger @ 450 kW.

For range extending options, electrification of the buses would enable the company to replace standard 8.9 liter engines with something smaller - in this case a new in-house developed 4.5-liter.

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, cutting displacement requirements in half.

"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

source: Green Car Congress, hat tip to Peter H!