The Hethel-based firm will be supplying its new EBus drivetrain which features the company’s APM200 spoke architecture electric motor, claimed to be the world’s most power/torque dense electric motor. The APM200, which also powers the upcoming Ariel HIPERCAR, will be paired with Semikron SKAI inverters, alongside lithium-ion battery technology.
“Each bus system has two APM200s and they’re mounted on a bespoke two-speed gearbox, which is part of the drivetrain system we’re supplying,” Ian Foley, Equipmake MD, told The Engineer.
“The spoke architecture [gives] a better use of magnetic flux, you get a higher torque density. In addition to that, we’ve also developed a system to directly cool the system with water because a limiting factor on the power density is the magnets getting too hot. A combination of those two things have enabled us to get the size and weight down.”
Agrale will integrate the electric powertrain into its MT17 chassis, a 12m single deck bus model capable of carrying 70 passengers. By optimising heating and cooling of the vehicle and maximising overall energy efficiency, the bus will have approximately 200 miles of range off a single charge – enough for a full day of operation. Overall weight will remain the same as the original diesel version. A prototype has already been built in Argentina, with full commercial availability expected by 2020.
“The key area for development with electric motors is really cooling,” Foley (left) explained. “There’s still a huge difference between the continuous power and the peak power of all electric motors. The more heat you get out the closer you can run it to peak power. All of our development is really focussed on how to improve the cooling [of] the motor and that’s the area we’re going to see big developments in the next few years.”
The motor relies on liquid coolant (water and glycol) circulating through the system, which has been designed for an inlet temperature of about 60°C. This is significantly cooler than an engine system, for example, and allows the powertrain to operate at increased efficiency.
“The water and glycol is circulated through the rotor of the motor, around the stator of the motor and through the heat sink of the power electronics,” said Foley. “There’s a pump and a radiator in the circuit and it's continuously circulated and then cooled to keep to a maximum of 60°C.”
The £2.5m development project is being supported by funding from Innovate UK and will see the first prototype vehicles testing in the UK in autumn 2018, with in-service testing starting in 2019 ahead of a projected on-sale date in 2020.
“We believe that electric buses will be proven to be cheaper than diesel buses over a 10-year period and therefore when the market gets confidence with the technology - effectively in about five years’ time - virtually every new bus is going to be electric," Foley said. "The market is huge and we are looking to roll out the model we’ve done with Agrale elsewhere, and supply to local bus manufacturers who need an electric drivetrain.”
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