Electric Bikes Motors: Technical
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Electric Motors: Technical
There are many possible types of electric motorized bicycles with several technologies available, varying in cost and complexity; direct-drive and geared motor units are both used. An electric power-assist system may be added to almost any pedal cycle using chain drive, belt drive, hub motors or friction drive. The power levels of motors used are influenced by available legal categories and are often limited to 250 W or 450 W, however there are some much higher power drives available [7].
Electric bicycles use rechargeable batteries, electric motors and some form of control. This can be a simple as an on-off switch but is more usually an electronic pulse width modulation control. Electric bicycles developed in Switzerland in the late 1980s for the Tour de Sol solar vehicle race came with solar charging stations but these were later fixed on roofs and connected so as to feed into the electric mains. [8] The bicycles were then charged from the mains, as is common today. Battery systems in use include lead-acid, NiCd, NiMH and Li-ion batteries.
Electric motorized bicycles can be power-on-demand, where the motor is activated by a handlebar mounted throttle, and/or a pedelec (from pedal electric), also known as electric assist, where the electric motor is regulated by pedalling. These have a sensor to detect the pedalling speed, the pedalling force, or both. An electronic controller provides assistance as a function of the sensor inputs, the vehicle speed and the required force. Most controllers also provide for manual adjustment.
Range is a key consideration with electric bikes, and is affected by factors such as motor efficiency, battery capacity, efficiency of the driving electronics, aerodynamics, hills and weight of the bike and rider. The range of an electric bike is usually stated as somewhere between 7km (uphill on electric power only) to 70km (minimum assistance). Some manufacturers, such as the Canadian BionX, have the option of using regenerative braking, the motor acts as a generator to slow the bike down prior to the brake pads engaging.[9] This is useful for extending the range and the life of brake pads and wheel rims. There are also experiments using fuel cells. e.g. the PHB.
A hub motor is an electric motor built directly into the hub of a wheel. A purported advantage of this design is that no additional transmission system is needed, thereby increasing the efficiency of the drive system. However, because electric motors are most efficient at high rates of revolution, direct drive hub motors tend to be inefficient. Integrated planetary gear drivetrains are sometimes include, but re-introduce transmission losses. They are commonly found on motorized bicycles. Hub Motor Electromagnetic fields are supplied to the stationary windings of the motor. The outer part of the motor follows, or tries to follow, those fields, turning the wheel to which it is attached. Energy is transferred to a brushed motor through physical contact of brushes to the rotating shaft of the motor. Energy is transferred to a brushless motor electronically, requiring no physical contact between stationary and moving parts. Brushless motor technology is more expensive, but most are more efficient and longer-lasting than brushed motor systems. Most of the hub motors made in China are designed for bikes with Chinese dimensions but these conversion kits are made to suit |
