A Novel Electric Vehicle Drive System

The conversion of vehicles from petroleum based fuels to Battery Electric Vehicles (BEVs) has been slow due to limited driving range and lengthy recharging times.A novel powertrain to increase utility of BEVs is being developed at the University of Arkansas -Fort Smith.The key component of this powertrain is the use of a 5-speed transmission matched with a specialized electric motor.This powertrain can be adjusted to match needed road performance and optimized for energy efficiency in passenger vehicles and light weight delivery vehicles.This project continues to build a bridge between local business, industry, and the University of Arkansas -Fort Smith in motor development and specialized parts needed in this powertrain.As this technology matures, it is foreseeable that new businesses and industries could result. Battery Electric Vehicle SpecificationsThe second generation BEV uses a 335 V system is powered by GBS LiFeMnPO4 batteries; these 60 Ah batteries are rated at 3 C to allow a constant output of 180 A for one hour and 600 A for 10 seconds.The prismatic battery set weights 550 pounds with an energy density of 100 Wh/kg.This second generation vehicle incorporates a 2.2 L, 5-speed GM transmission to better match driving conditions.Figures 1 through 4 provide data for motor shaft speed and torque which is coupled in the final design to a 5-speed transmission.Figure 1 shows the motor speed produced as the dynamometer increases the load torque until motor stall or pullout.Peak torques is achieved between 1200 to 1780 RPM. Figure 2 indicates the peak 146 A current demand is at 1780 RPM producing a maximum torque of 150 Nm.The produced torques shown in Figure 2 were not limited by drive current as the motor drive was oversized and could sustain 150 A continuously.The set of curves highlighted in Figure 3 indicate the predicted motor torques needed for first through fifth gear applied to the 5-speed transmission to accelerate a 1900 kg vehicle from 0 to 60 MPH in 10 seconds.The yellow zone in this Figure 3 indicates the vehicle can be accelerated using third or fourth gear of the transmission while staying within the torque limits of the traction motor.Figure 4 indicates motor torque needed to maintain a constant speed traveling on level ground; this torque demand includes rolling and air resistance.With the 5speed transmission in fifth gear, the needed motor torque is 93 Nm at 1660 RPM which is equal to a vehicle speed of 60 MPH.This falls within the limits of the motor/drive capabilities.Figure 4 also indicates a maximum vehicle speed of 80 MPH is obtained with the transmission in fifth gear.Figure 5 is a photograph of the traction motor used in this project.This motor is totally enclosed to protect against dust and water damage.The motor also has an aluminum frame to quickly dissipate heat and reduce weight.