Cordon, D., Wos, S., Beyerlein, S., and Odom, E., "Highly Integrated Parallel Hybrid Powertrain," SAE Technical Paper 2012-32-0026, 2012, doi:10.4271/2012-32-0026.
This paper details a multiyear effort at the University of Idaho to develop a very compact powertrain that results in a lower center of gravity and smaller pitch and yaw inertia for a single-seat open-wheeled hybrid competition vehicle. This design entails introducing torque from the electric motor to the countershaft of a Yamaha YZ250F engine, allowing torque multiplication via the transmission and thus to the final drive and wheels. Maximum motor speed into the countershaft corresponds to maximum speed of the engine. The repackaged powertrain features a D135RAG Lynch electric motor connected to a customized countershaft that is housed in a machined aluminum case that includes Original Equipment Manufacturer (OEM) engine and transmission internals. This case also incorporates a Torsen differential with an in-house designed planetary gear reduction. Low-end torque and fuel economy are enhanced through implementation of electronic fuel injection as well as reliable low-speed torque from the electric motor. The cylinder and head were angled rearward for tighter packaging behind the driver. The whole powertrain, including the electric motor and differential, is less than 1000 mm long and weighs less than 45 kg. The system produces 23-26 N-m of crankshaft-resolved torque across the operating range of 4500 RPM to 13,000 RPM, and has a peak power output just over 30 kW.