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Test Data

Seoul National University of Science & Technology (Eco Automotive Technology Institute)

Test Data
RPM vs. Efficiency
Main Drivers for Increase in Efficiency
Single Speed EV Efficiency Analysis
EV Cost Reduction for Auto Makers
Single Speed EV Efficiency Analysis
Reasons why efficiency steeply decreases at higher rpm range?
● Because most automotives are driven in urban area with lower velocity, current electric vehicles are set their rated RPM at lower range (as showed on the efficiency graph in next page, Tesla set its rated RPM in the range of 20~30 mile/h). This results in efficiency and hill climbing ability in the city area is higher than those in highway driving.

● In spite of controlling velocity using field weakening technology in the constant voltage region, efficiency steeply decreases as RPM increase (refer to the below graph).

● Using motors out of the range of rated RPM subsequently causes overheats in windings, which results in energy losses and stalling motor. Because electric vehicles covers wider range of speed from 0 to 150km/h, field weakening control solutions have been developed. However, it has not solved efficiency problems
Range vs. Constant Speed
[Source : http://www.tesla.com ]
How to get high efficiency?
Solution is Multi-speed transmission
In-wheel 5-speed transmission(Non-hydraulic auto)
(Bygen’s disruptive technology)
Motor rotates at rated RPM range at any velocity range, which runs within high efficiency range,
It has no hydraulic equipments to bring complexity and heavy weight,
Small and light design enables in-wheel type without energy losses of power shifts,
For the same performances comparing to single speed EV, motor output of a half power is enough.



Make efficiency increase double than single speed .