A group of Wayne State University (WSU) Hybrid Warriors finished the design and integration of their custom gearbox which is now running in the vehicle. The WSU vehicle architecture is a Parallel through the Road plug-in hybrid electric vehicle. The power of the rear drivetrain comes from a Remy electric motor. Before running the rear wheels, the torque of the motor must be amplified to meet the acceleration performance, and its speed must be reduced to match the required wheel speed. The WSU Hybrid Warriors chose to build a custom-designed gear box for this purpose.
Previously, they had a belt-drive reducer, but it’s susceptible to slip and wear at high torque. Especially in the mode switch between driving and regenerate braking, the alternate change of stress direction gives rise to the fatigue break. To get rid of this issue the project of designing a single-speed gearbox had been put forward. “It’s a challenge and a risk for us to make a custom-designed gearbox; however, a custom-designed gearbox fits our overall structure much better, and it’s a great practice for engineering students,” said one of the project members.
The gear ratio had been set as 2.5, which forms the final 6.925 reduction ratio for the rear drivetrain when it connects to the rear differential. In order to get smooth operating, Helix teeth had been applied to the gear set and tapered roller bearings had been picked to sustain the axial loads stably.
One challenge the team faced is giving the gear set a strong carrying capacity in their limited vehicle space. To overcome this difficulty, the team requested the gear manufacturer from team sponsor Ka-Wood to do heat-treatment and shot-peening besides using high strength material. Another big challenge is assembling the gearbox. The gears are fabricated by the manufacturer while the cases are fabricated by the university machine shop. The students had to assemble all parts together and keep an accurate fitting by themselves.
It’s an exciting experience for the WSU Hybrid Warriors and the team is looking forward to showcasing their gearbox at the Year Three Competition in less than two weeks!