Engineers at Colorado-based UQM Technologies have collaborated the past several months with their counterparts at Eaton’s Vehicle Group and Pi Innovo, both located in Michigan, to develop a full electric drivetrain system for the medium- and heavy-duty EV markets.
Eaton experts are developing and supplying to UQM a 2-speed transmission for an EV (electric vehicle) application, and Pi Innovo engineers are responsible for the transmission control unit. The components are integrated with UQM’s current PowerPhase HD220/HD250 motor and inverter system to create a full electric drivetrain system called the UQM PowerPhaseDT.
Benefits of the new drivetrain, according to Josh Ley, vice president of technology for UQM, include better packaging, efficiency, greater payload capacity and lower cost when compared with direct drive or single speed drivetrain strategies.
“Perhaps the biggest benefit is the fact that the 2-speed transmission keeps the electric motor operating in the highest efficiency region for a greater portion of the drive cycle,” said Ley. The Eaton 2-speed transmission provides a greater speed and torque range from what would normally be possible in a direct drive system, he noted, allowing a smaller electric motor to drive large vehicles.
First gear ratio is 3.53:1, and second gear is 1:1. Peak torque is rated at 3050 N·m (2250 lb·ft), with a continuous torque range of 1200-1420 N·m (885-1047 lb·ft). Rated power ranges from 150-180 kW, with peak at 250 kW.
“Even with the transmission, the total size and weight [of the system] is smaller than the motor that [typically] would be employed without a transmission,” Ley explained to Off-Highway Engineering. “Our motor is 250 kW, but it is very small for that power level. Motor’s size basically [depends] on torque required; therefore the transmission allows massive downsizing.”
Efficiency benefits also lead to cost reduction. “The high efficiency band is large so you only need 2 speeds as opposed to 4 or 5 to match the power band of an engine,” he said. “Higher powertrain efficiency translates directly to increased range or reduced battery costs—or both.”
The drivetrain is targeted to electric and range-extended commercial vehicles up to 18,000 kg (39,700 lb). Ley believes the system would be an “excellent” fit for off-highway applications.
“The low-range first gear can help off-road vehicle makers to provide a very low overall drive for low-end torque,” he told Off-Highway Engineering. “Similar designs for both the UQM motor and Eaton transmission have been used in off-road applications [previously].”
UQM is ready to deliver prototypes to customers this fall as part of the initial pilot program. The company already has secured Hybrid Kinetic Group, Wuzhoulong Motors and ITL for a Yangtse full-size bus in China, and California-based Adomani in the U.S. Applications for early PowerPhaseDT adoption include transit buses and school buses.
Start-of-production units are on target for early 2017 delivery.
“It is a short development cycle, but most of the major components had been validated and proven in applications previously. The focus of the development is system-level powertrain controls,” Ley said. “We are designing the system such that system controls integration with vehicles is very convenient, while still supporting expanded functionality. The Pi Innovo and UQM teams have extensive experience with vehicle systems integration.”
Beyond satisfying customer drive cycle needs, the full electric drivetrain system will be a contributor in helping vehicles meet more stringent environmental regulations, Ley believes.
“Phase 2 regs are aggressive. I would anticipate many of the OEMs going full electric, series hybrid or plug-in range-extended electric vehicles (REEV),” he told OHE, referring to the recently finalized U.S. EPA and National Highway Traffic Safety Administration greenhouse gas (GHG) rules for medium- and heavy-duty vehicles from model year 2021-2027.
“This drivetrain system applies to all three types of vehicles. The higher efficiency of the system will decrease carbon emissions for the hybrids. Essentially the pure electrics are no emissions inherently, but it certainly improves the business case of the fleet having lower kW·h consumption from the utility,” he said.