What’s Driving Electric School Buses? A
Written by Mark Rowh
re all electric school buses basically the same? Perhaps that’s largely the case, but the move- ment toward electric vehicles has brought some important distinctions in vehicle com-
ponents.
The primary differences between internal combustion and electric vehicles, of course, are the battery packs powering the vehicle, followed by the replacement of the engine and traditional transmission with electric drivetrains. Yet no single approach has become the indus- try-wide standard with either drive trains or batteries.
Evolving Drivetrains The potential offered by electric axles has garnered a
good bit of attention recently, with options such as the Blue Horizon 14Xe ePowerTrain, introduced by Meritor, promising new levels of efficiency. While some OEMs are now making the transition to e-axles, others are tak- ing a wait-and-see approach. With the acquisition of Meritor by Cummins, ev- erything that was under the Blue Horizon umbrella has been integrated into the Accelera by Cummins zero-emissions product portfolio, including the ELFA inverter line and traction motors from Siemens. “The 14xe is already in production and we are launch- ing more axles and solutions over the next few years,” said Saad Malik, executive director of the traction product Line for Accelera. He noted that e-axles with integrated transmissions are more efficient than central drive systems. “They take up less space and leave more space for
batteries or a lighter weight, smaller vehicle if needed,” he said. Malik added that advantages to having Accelera-made
components integrated on the e-axle include the ability to tune the inverter, motor and transmission for optimal energy efficiency and performance. Meanwhile, the adoption of electric axles by Thom-
as Built Buses has been in the plans for some time, although progress has been slower than originally antic-
ipated. In 2021, plans were announced to adopt the Blue Horizon 14Xe by this past January, but implementation has been pushed back to early next year, explained Arjun Nair, manager of the EV program and consulting for Daimler Trucks North America. He pointed to significant progress seen in recent years, including lessons learned from the trucking end of the industry, which in the case of Thomas Built, means that of parent company Daimler. “It’s part of the DNA as we share our learning across the
company,” he said. “There’s a lot of learning that we share with our colleagues on the truck side and vice versa.” This includes developments in e-axles, where the pro- cess has informed adjustments in factors unique to buses. “If you look at the electric school bus market, those
with the longer wheelbases are the ones that are electri- fied and with the e-axle that allows us to go shorter on the wheelbase, so that is one big benefit,” Nair continued. “And the technology is improving and is expected to be more efficient.” GreenPower Motor Company, on the other hand,
hasn’t made the switch to electric axles. But Brendan Riley, GreenPower’s president and director, said his team continues to monitor development for possible use in the company’s school buses, which feature a design with the body integrated on the chassis as a unitized struc- ture. For the drivetrain, the vehicles use a conventional layout with a motor mounted longitudinally and the driveshaft going into the axle. “They’re medium-duty products,” Riley said, noting
the design works well in dealing with the way buses typically operate, such as slowing down frequently. Thus far, Riley said his company’s reluctance with electric axles stems from concerns about strains and vibrations that can negatively impact vehicle stability. But he’s not ruling them out in the future. “Right now, we’re evaluating them, and we do think
that e-axles offer a viable solution,” he added. “They look like they’re getting very compelling.” Blue Bird is another OEM not currently using e-axles. A single speed direct drive system has been in place
www.stnonline.com 29
Funding aside, progress continues when it comes to e-axles and battery technologies
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52
