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Friction Reduction is the key to Energy ConservationThe key to energy conservation is the elimination of a gearbox when using
electrically powered motors. These gearboxes' sole purpose is to compensate
for the contradictory power needs during the range of operations. To
accelerate an electric motor or to run at cruising speed requires different
power settings. The nominal and maximum torque is, however, by far the
most important factor. Electrically powered vehicles have extremely
dynamic traction requirements:
The maximum number of kW delivered by the gearbox must therefore be 350 Nm * 2500 / 9550 = 91.62 kW. The rated gearbox efficiency is 93% (2 stages) which gives a net consumption of 6,44 kW net by the gearbox. There is 91.62kW * 93% = 85.18 kW; 91.62 - 85,18 = 6.44 kW lost. The motor, which gives 350Nm in the start, can only bring 12 kW at cruising speed (2500 RPM). There is a loss of energy of: 6.44 kW / 12 kW * 100% = 53.6%. Such a bus has a starting efficiency of less then 50% under nominal working conditions.
Applying a gearbox to an electric motor can,
therefore, be likened to the legend of the Trojan Horse. A gearbox,
which can be likened to the "enemy" within, adds friction,
requiring usually twice the amount of energy truly needed for the desired
movement. That is twice the amount of battery power (which adds weight
and cost again more energy) or twice the amount of fuel to run an oversized
generator is needed to move the vehicle or device. A. Measure the battery current at maximum revolutions of the motor(s) with wheels raised off the ground, then.. B. Measure the battery current of the motor(s)
with wheels on the ground at driving full speed on the ground. See also: Mechanical Efficiency |
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