An electric bicycle, also known as an e-bike, is a bicycle with an electric motor used to power the vehicle. Electric bicycles use rechargeable batteries and can travel up to 15 to 20 mph (24 to 32 km/h). Electric Bikes are simple to operate and maintain combining pedal power with a silent and powerful electric motor that can travel up to 30 miles a charge. In some markets they are rapidly replacing traditional bikes and motorcycles.
Electric bicycles are classified as bicycles rather than motor vehicles, so they are not subject to the more stringent laws regarding certification and operation of motor vehicles. Electric bicycles are one type of motorized bicycle. However, electric bicycles are defined separately and treated as a specific vehicle type in many areas of legal jurisdiction.
Electric bicycle usage worldwide has experienced rapid growth since 1998. It is estimated that there were roughly 120 million e-bikes in China as of early 2010, and sales are expanding rapidly in India, the United States of America, the Netherlands,and Switzerland. A total of 700,000 electric bicycles were sold in Europe in 2010, up from 200,000 in 2007 and 500,000 units in 2009.
MOTORS, BATTERIES, AND CONTROLLERS
Motors and drivetrains
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. BLDC hub motors are a common modern design with the motor built into the wheel hub itself and the stator fixed solidly to the axle and the magnets attached to and rotating with the wheel. The bicycle wheel hub is the motor. The power levels of motors used are influenced by available legal categories and are often, but not always limited to under 750 watts.
Electric bicycles use rechargeable batteries, electric motors and some form of 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. 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.
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 7 km (uphill on electric power only) to 70 km (minimum assistance) and is highly dependent on whether or not the bike is tested on flat roads or hills. Some manufacturers, such as the Canadian BionX or American E+ (manufactured by Electric Motion Systems), have the option of using regenerative braking, the motor acts as a generator to slow the bike down prior to the brake pads engaging. 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. Some experiments have also been undertaken with super capacitors to supplement or replace batteries for cars and some SUVS.
The energy costs of operating electric bicycles are small, but there can be considerable battery replacement costs. Riding an electric bicycle to work or to the store instead of taking a car has long term financial and health gains.
Control can be as simple as an on-off switch but more usually they are 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 pedaling. These have a sensor to detect the pedaling speed, the pedaling force, or both. Brake activation is sometimes sensed to disable the motor as well.
There are two distinct types of electric bike controllers designed to match either a brush or brushless motor. Brushless motors are becoming more common as the cost of controllers continues to decrease. The page on DC motor covers the differences between the two types.
Electric bicycles require high initial torque and therefore models that use brushless motors typically have Hall sensor commutation for speed measurement. An electronic controller provides assistance as a function of the sensor inputs, the vehicle speed and the required force. The controllers generally provide potentiometer-adjustable motor speed, closed-loop speed control for precise speed regulation, protection logic for over-voltage, over-current and thermal protection. The controller uses pulse width modulation to regulate the power to the motor. Sometimes support is provided for regenerative braking but infrequent braking and the low mass of bicycles limits recovered energy. An implementation is described in an application note for a 200 W, 24 V Brushless DC (BLDC) motor.
Brush motors are also used in electric bikes but are becoming less common due to their intrinsic lower efficiency. Controllers for brush motors however are much simpler and cheaper due to the fact they don’t require hall sensor feedback and are typically designed to be open-loop controllers.