The recent demand for more powerful and reliable
Light Electric Vehicles has resulted in tremendous
advancements throughout this industry over the last
couple of years. While for the pedal bikes with
electric assist currently the reduction of weight
is the main priority, the electric scooters and
motorcycle market is demanding more power on the
road and increased range.
High torque is a paramount requirement especially
for the electric motorcycles since they must keep
with the acceleration and hill climbing of the regular
fuel powered traffic.
Specific research and development for suitably
powered electric bike motors have been undergoing
for several years. It started with the prevailing
500W motors five years ago, then gradually the available
power has been enhanced to 1000W, 1200W, 1500W with
the aim to provide an experience that compares to
the available gas powered motor scooters currently
on the market.
Up to this point standard electro-magnetic laws
applied in motors have fought over contradicting
restraints since motor torque and speed fight against
Hence thereof arrives the main problem for all
electric motorcycles manufacturers: on one side
they need a high starting and climbing torque, on
the other they need a high speed of at least 60km/h.
The easiest way to have a descent torque and high
speed is to provide high electric current to the
motor at start-up and during acceleration. Many
manufacturers of electric motor bikes are designing
their controllers to provide 80, 100 or even more
amperes current to the motor. This causes several
1. If the current drawn from the batteries exceeds
1.5c (1.5 times than the battery capacity), the
life of the battery or more specifically the available
number of charge cycles will be greatly reduced.
This means that for 40AH battery the maximum current
should not go beyond 60A.
2. When the motor is used on long hills high current
can cause the motor to overheat which eventually
degrades winding insulations to the point of premature
failure. Brushed motors have additional problems.
High current causes sparking between the contacts
(between the commutator and the brushes) and unwanted
ashes and abrasives are being deposited inside the
3. High current also creates a bottleneck effect
affecting the available voltage to the drive system.
Very high current creates a voltage sag along the
limited size power conductors which reduces the
motor power especially on start and when going uphill.
This explains in many cases why a an excessive needle
drop of the voltmeter gage can be noticed when full
throttle is applied on a 1500W motorcycle that consumes
80A for example.
Technically even a newer generation high efficiency
1500W brushless direct drive electric motor at its
highest speed of 600rpm (45-50km/h) can produce
only a torque of around 15Nm. This limits its climbing
ability to around 6 degrees. Even if the motor controller
set-up is optimized for slow start-up speed the
controller must provide peak power that is much
larger than the motor rated output power. Pumping
in more current artificially increases the motor
power and pushes the batteries, the motor and the
controller beyond their sustainable limits and leads
to premature failure. For example to reach a torque
of 40-50NM with the 1500W rated brushless motor
described above we need a peak power of 3000W. Since
the motor is not designed for low speed, during
start-up and when we go uphill its efficiency drops
to 50-60% and this must be compensated with even
higher current of 90-100A.
Providing a high current requires the use of high
capacity heavy batteries and still in many cases
a healthy current draw of 1-1.5c can not be achieved.
To reduce or avoid high current detrimental impacts
the manufacturers often either reduce the performance
of the electric motorcycles or provide the motor
with a thermo-mechanical overload protection which
often reduces the reliability and availability of
the vehicle. To reduce the harmful effect of the
high current some manufacturers are providing dual
speed motorcycle based on high and low current limits.
This however only restricts the current provided
to the motor and reduces its performance especially
on hills. Obviously, the big current is one of the
most limiting factors which impact the stability
and growth of the e-vehicle industry.
Greenwit Technologies' newly designed electric driving
system for the MOTORINO™ line of motorcycles
eliminates most of the problems related to high
powered brushless electric motors. It is based on
a proven and very efficient concept. We have been
able to effectively integrate in one housing an
optimized high and a low speed brushless motor and
combined it with a matching intelligent dual controller.
The motor controller pairs are selected depending
on driving conditions. An electronic automatic gear
shifter commanded by a speed sensor automatically
shifts between the two motor modes. In this way
a high torque of 90Nm with a speed of 30km/h and
20Nm with a speed of 60km/hr can be achieved. In
both high speed/high torque modes the maximum current
is 45A. The efficiency is 87-90% in the two “motors”
since each “motor” is coupled with a
customized controller drive circuit and there is
no need to overpower a motor designed for high speed
for high torque performance. This concept also allows
the use of lower capacity batteries of 38AH or less,
reducing the weight of the bike which further adds
to the overall efficiency. This high efficiency
design makes it possible to achieve significantly
longer ranges when compared with current brushed
or brushless single speed systems.
TECHNOLOGIES Inc is currently developing
3 and 4kW high efficiency brushless motors specifically
designed for converting larger engine gasoline motorcycles
(125cc and up) into electric. They are expected
to be available in spring 2007.