Question

Consider an e-bike is designed according to EN 15194 standard (pedal assisted and all electric driving modes with the maximum 250W rated output power and electric motor assist is cut-off at 25km/h). Assume the mass of the bicycle is 24 kg (including electric motor and battery) and the mass of rider is 75 kg. The rolling resistance coefficient of bike tyres is 0.007. The bike is using a direct drive brushless DC motor (hub motor) mounted in 29 inch-rear wheel (see below figure). a. Find the rotating speed of motor (as rpm) and the bicycle speed (as km/h) for the condition that the bike is cruising on a flat. And calculate the motor torque. Hint: please select the proper values of air density, frontal area of bicycle and aerodynamic drag coefficient. Comment on the operation of the e-bike drive system in this question. b. Find the electric motor torque at cut-off speed (25 km/h). c. Assuming the maximum output power is confined at 250W by the motor driver, find the maximum road grade angle that the bike can climb at 10 km/h. d. Assuming the battery voltage is 48V, calculate the energy capacity of the battery for two-hour all-electric driving on flat road with 250W motor power (assume the motor-driver overall efficiency is 90%)

Answer 1