This text is literally taken from ETRA for PRESTO-project, Policy guide electric bicycles, WP2 deliverable 2.3, p. 40 and can also be downloaded from: www.presto-cycling.eu
Gears
Since the introduction of indexed shifting, changing gears is very accurate and simple either by pushing a button or turning a handle. The gears are either integrated in the hub or external. There are gear hub systems with 3, 4, 5, 7, 8, 9 and even 14 gears integrated and shielded from dirt, humidity, damage, … Alternatively the bicycle is equipped with 2 derailleurs for up to 27 gears. There are also systems, which combine a gear hub with a derailleur.
In recent years, NuVinci introduced an innovative and "ground-breaking" gear control system to the (E-)bike world. This system can be compared with the Variomatic, the continuous variably transmission system which DAF developed in the fifties. A set of rotating spheres transfers torque between two ´rings¡. Tilting the spheres changes their contact diameters on the rings, allowing an endless progression of speed ratios. This results in smooth, seamless and continuous transition to any ratio within its range.
Motor
The motors used in electric bikes are DC (Direct Current) types that operate with a power supply, the battery, which is also a DC power source. Most DC motors used in electric bikes are of the brush-less type. Brush-less motors use permanent magnets of the Neodymium-Iron-Boron type. The Neodymium magnet, also called REM (Rare Earth Magnet), is the most powerful allowing the motor to be lighter and smaller than older designs that used ferrite magnets.Brush-less motors
An important functional issue for motors is that brushes wear out, thus limiting the motor’s life. A brushless motor will last much longer than a brush type motor – with the only limiting factor being the life of the bearings. Motors that have fewer parts, such as brush-less, sensor-less designs are both less expensive to build and have fewer failure points.Hub motors
The most common pedelec motor currently on the market is the hub motor located in the hub of either the front or the rear wheel. There are Japanese pedelecs that use a motor mounted near the sprocket that is mechanically coupled, via gears, to drive the sprocket.Hub motors use a space that is not otherwise used by a conventional bicycle design – making the addition of a motor easy and elegant. Additionally, the hub motor wheel that simply bolts into place in a normal bicycle frame reduces the need for engineering or design changes, and fits into the assembly / sourcing processes of the normal bicycle industry. However, hub motors, due to their confined space and the complexity of adding internal, changeable gears, are less efficient than a bottom bracket drive – and cost slightly more.
Rear hub motors seem to be the most logical solution, but it must be possible to mount gear clusters for the human powered bicycle chain – an extra cost. Front hub motors are simpler to design and install. They give the bicycle two-wheel drive as the human power is always applied to the rear wheel. Front wheel drive bikes, when properly designed, ride as well as rear wheel drive bikes.
Manufacturers of hub motors for pedelecs can be found in Europe, Asia and North America. Around 95% of all pedelecs use hub motors. Most pedelec motors in Europe range in power output between 0.25 and 0.4 kilowatts. Designs of motors for pedelecs will continue to improve to increase torque performance and efficiency as well as to reduce size and weight.
Speed limits
A pedelec equipped with a speed sensor will require the rider to pedal a few strokes before the motor starts. The EN 15194 standard permits for pedelecs from 0 to 5 km/h, that the motor can provide the main power for propulsion. When the speed exceeds 5 km/h the pedals most be utilised and current is progressively reduced until the bicycle reaches as speed of 25 km/h.Source: ETRA for PRESTO-project, WP2 deliverable 2.3, p. 40
