Lightweighting is an important goal for electric vehicles. One novel idea being tested by engineering students at Bradley University is the use of polyacetal (POM) in power transmission gears in an Ultra Light Urban Vehicle project.
The project is the brainchild of Martin Morris, professor of mechanical engineering at Bradley, which is located in Peoria, IL. It’s a 3-wheeled vehicle licensed as a motorcycle that carries two people, baggage and weighs 430 lbs. It offers regenerative braking, a top speed of 45 mph and a range of 40 miles.
“Traditionalists would say harsh transmission applications preclude POM,” says Tim Brogla, program developer, DuPont Performance Polymers, which supplied polyacetal for the gears “Clearly, this project challenges some of those ‘absolutes;’ it doesn’t require a leap of faith to see these gears in small engine transmissions, such as riding lawn mowers and golf carts.”
Winzeler Gear, based in Harwood Heights, IL, and one of America’s three largest plastics gear molders, provided design and manufacturing support.
“The high-performance nature of a homopolymer acetal can manage the torque and load while delivering low friction and reduced noise,” says Mike Cassata, design engineer, Winzeler Gear. “The planetary transmission gears of Delrin POM must withstand the torque produced by a 25 horsepower motor @ 6,000 RPM.”
The innovative gear transmission consists of a 14-teeth, 3-module, 42 mm diameter sun gear mounted to the motor shaft. The sun gear drives 4 planet gears with 17 teeth and a 51 mm diameter coupled to the output carrier shaft assembly. The planet gears rotate in a fixed internal gear with 50 teeth and a 150-mm diameter. All gears are 25-mm facewidth.
Gears can be machined from bar or plate stock of Delrin, significantly cutting cost and time while delivering mechanical properties comparable to the injection molded gears.
Photo shows an ultra-light electric vehicle designed by Bradley University engineering students.