A rear-wheel-drive sports car’s estimated triple-digit mpg and predicted 5.7-s 0 to 60 mph (0 to 97 km/h) acceleration time are the prime performance cues associated with a hybrid-electric retrofit that features multiple innovations.
Engineers at Mississippi State University’s Center for Advanced Vehicular Systems (CAVS) are creating fresh solutions via electrifying a 2013 Subaru BRZ.
“On our other product-driven projects, we don’t always have the flexibility to create intellectual property for the university. With this project, we can divert resources to follow ideas that show promise,” said Matthew Doude, CAVS’ Program Manager - Powertrain Engineering Business Development Officer. Doude is the project leader for the Subaru BRZ conversion, dubbed The Car of the Future.
The project’s first phase involved replacing the BRZ’s 2.0-L four-cylinder Subaru Boxer engine and six-speed manual transmission with electrification technologies that transformed the production model into a more fuel efficient, higher performing two-door sports car, according to Joseph Gaddis, CAVS Research Engineer.
“We put about 400 miles on the all-electric car, which had a range of 30-40 miles,” said Gaddis. “For the second phase of the project, we now have a hybrid-electric sports car with a 0-60 mph time that’s faster than the stock Subaru BRZ. The car gets 104 mpg combined city/highway and has a total range of 550 miles,” Gaddis said. Fifty miles of all-electric mode driving is possible before re-charging the battery pack.
The hybrid-electric car has two electric drive motors, an 850-cm³ two-cylinder gasoline engine, and seven lithium-ion battery cells. Three of the cells are packaged in the engine bay, and four cells are in the transmission tunnel. The original transmission tunnel was replaced with a custom-built tunnel.
CAVS technical specialists designed and developed a unique battery cooling system that was built by Luvata. “We’re side-cooling the battery pack using very, very small cooling channels,” Gaddis said. CAVS will apply for a patent on the system. “It’s the non-traditional packaging and unique components that make our system so innovative,” said Gaddis.
When development work is complete on a charging port, a patent will be sought for a charging unit that can be used on any electrified vehicle.
“We expect that this charging port will be the first of its kind on the market,” said Gaddis, adding, “The way that the charging port opens and the way that it fits on the car will be unique.”
MSU’s CAVS demonstration car is fitted with several 3D printed parts. Said Gaddis, “Our engine covers, air box, the components inside the battery pack, and part of the center console are 3D printed nylon parts, and the shifter knob is a 3D printed stainless steel component.”
Predictive powertrain control management, a form of model predictive control (MPC), provides the car with connected car capabilities, according to Michael Mazzola, Associate Director for Advanced Vehicle Systems at CAVS and MSU professor of Electrical and Computer Engineering.
“We are implementing a relatively easy MPC application called ‘battery state-of-charge control.’ This works on the powertrain level only, but the results show fuel consumption is almost identical to that of duty-ratio control while relaxing the amount of battery cycling to reduce internal heating and increase the battery life.”
The team’s future MPC plans include adding a so-called ‘planning layer’ for MPC function in a more sophisticated hierarchical mode.
“This means that we will get connected to the larger transportation system through cloud-based information that private and public organizations are making available,” said Mazzola. One possible example, the smart powertrain, recognizes the driver’s normal commute route and determines if an upcoming traffic condition, such as an accident, would prompt a route change and a re-compute of the best way to use the stored battery energy from an overnight charge.
“There are many, many variations on this theme. So many [possibilities] that federal, state, and local agencies are partnering with the private sector to make our transportation system friendly to the connected vehicle, which the MSU Car of the Future aspires to be,” said Mazzola.
A phase-three development undertaking is under consideration for the demonstration car. Said Gaddis, “We might make additional modifications that would make this rear-wheel-drive car an all-wheel-drive car with torque-vectoring capability.”