Cummins Unveils Electrified Powertrain For Transit Buses

Continuing its expansion into electrified powertrains, Cummins is unveiling a new powertrain targeting transit bus applications at the APTA public transportation show in Atlanta.

The company’s new powertrain is configurable for either a full battery electric vehicle (BEV) or a range extended electric vehicle (REEV) incorporating a compact engine-generator. Cummins said its electrified power systems enable direct drive-by-wire continuous acceleration for transit, shuttle and commuter buses and when operating in battery-only mode, the system achieves zero emissions at the point of use.

Enhanced energy storage for both the BEV and REEV systems is achieved using Cummins’ high-density battery enclosure, which are compact and modular allowing for both on-roof and chassis integration. Cummins said its battery enclosure design fits into existing bus configurations.
Proprietary control technology enables the zero-emissions bus range to be extended by optimally managing subsystems, allowing the charge of the battery to be extended, Cummins said. Operational flexibility is also improved with fast recharge capability using a plug-in connection, as well as options for enroute charging when a pantograph or charge plate infrastructure is available.

“The introduction of our new BEV and REEV systems will complement Cummins’ clean-diesel, near-zero natural gas and diesel-hybrid products to offer the broadest, most energy-diverse power portfolio in the bus industry. We are able to meet the needs of every transit route, every duty cycle and every emissions standard in the most cost-effective manner,” said Julie Furber, executive director, Electrification Business, Cummins Inc.

The standard-size Cummins battery enclosure provides a 70 kWh storage capability with up to eight enclosure units storing 560 kWh able to be installed within a BEV bus. This enables a zero-emissions range of up to 224 miles on a single charge, with a diesel-equivalent mileage of 25 mpg.

Cummins REEV system has a battery pack of three enclosures totaling 210 kWh which can provide a zero-emissions range of up to 84 miles, which is a significant advantage over current hybrid bus capability, the company said. When the battery pack depletes to a low state-of-charge, the REEV system brings online a 150 kW/201 hp engine-generator system to recharge the batteries.

Compared to the standard diesel-powered bus, the 4.5 L engine used in the REEV system is downsized by about 50% in terms of displacement and can achieve up to 10 mpg, Cummins said. A power assist function is available from the battery pack whenever the system needs additional energy.
The REEV system’s ability to switch between shorter-range battery-only mode and extended-range generator mode allows transit authorities to geofence specific downtown areas by utilizing Cummins over-the-air connected technology. The REEV system also enables buses to travel significant distances beyond the city charging infrastructure, Cummins said.

“A key focus in the design of both our BEV and REEV systems ensures the electrified architecture is modular and adaptable to enable an easier technology transition for bus manufacturers,” said Brian Wilson, Cummins general manager — Global Bus Business. “This allows transit authorities to continue using the same preferred bus models and retain fleet commonality.

“The new systems will be expertly serviced and supported by Cummins’ distribution network the same way we currently provide 24/7 support for our diesel-, hybrid- and natural-gas-powered fleets. This is an important factor for transit authorities, because as they adopt new technologies they can count on Cummins to help with a transition to BEV and REEV technology.”

The BEV and REEV systems incorporate the same traction motor and power electronics to deliver a continuous torque output of 1850 Nm/1365 lb. ft., eliminating the need for gear shifting and dramatically reducing powertrain noise, Cummins said. When the vehicle requires additional tractive power during rapid acceleration or while climbing gradients, the system can deliver an instant peak torque boost of up to 3400 Nm/2508 lb. ft. for a short period.

Both systems provide a continuous electrical output of 225 kW/302 hp, increasing to a peak output of 350 kW/469 hp when it senses the need for a power boost. The high-voltage system operates at a nominal 660 V when battery state-of-charge is around 50%.

Battery energy storage levels are boosted on-route by accepting “free” energy recovered through regenerative braking. On a frequent stop/start bus duty cycle, this could contribute the equivalent of 20% to the total state-of-charge, the company said.

Electrical energy is also exportable from the Cummins system to all electric-powered accessories featured on the bus, such as e-power steering, e-HVAC, e-air compressors and e-cooling fans, adding up to a typical 25 kW/33 hp load at any one time. The electrical supply from the Cummins system can be both low-voltage dc and high-voltage ac, which the company said can help to simplify the installation and lower the cost of the e-accessories package.

The same electronic control module used on the L9, L9N and B6.7 bus engines is adapted for use as the BEV and REEV system controller, offering familiar diagnostics and the connectivity to bus operators.