How does an electrically assisted bicycle work?

The electrically assisted bicycle is one of the original solutions for urban mobility. It is also a practical means of transportation, as it allows you to get from one place to another in less time than it would take a car to get through traffic jams.

The electric bicycle is also an ecological and sustainable alternative: no greenhouse gas emissions, micro-particles or toxic fumes. This explains why it is so popular with cyclists.

If the electric bike has many advantages, it is necessary to know how it works for an optimal handling in everyday life. We will first talk about its different components before tackling the mode of use of this type of locomotion.

Quel est le fonctionnement d'un vélo à assistance électrique ?-1

What are the different components of an electrically assisted bicycle (EAB)?

An EAB is a hybrid type of bicycle that combines the cyclist's pedaling power with a motor located either in the pedals or in the wheels (front or rear). Before buying a bike, it is important to know how it was designed, manufactured and assembled. It is even more useful to know its anatomy to better understand its functioning. The key components of an electric bicycle are the same as those of a conventional bicycle. However, other components, such as a motor, a pedaling sensor, a battery, a control console and a controller, have been added to enable electric assistance.

The motor

The motor assists pedaling. The European legislation for an EAB stipulates that the motor power must not exceed 250 watts for a maximum speed of 25 km/h. At this speed, the motor must stop and switch off as soon as you stop pedaling. There are several types of motors on the market, each with specific features that go beyond the characteristics advertised by the manufacturer. However, in order to have an intuitive riding experience, the motorization of an eBike must be provided by a reliable and recognized brand. This guarantees the power and durability of the motor.

The pedaling sensor

The pedaling sensor, which measures the pressure on the pedals and adjusts the assistance, is located inside the motor. It triggers and controls the motor according to pedaling. It's simple: without pedaling, the sensor can't detect any movement, and the motor doesn't start. This also explains why the motor shuts off when the cyclist stops pedaling. This is also called a "torque sensor" or "power sensor".

There are other sensor technologies:

  • speed sensor: it is located on an external sensor type meter with magnet on the rear wheel (in the case of a pedal motor) or in the wheel (in the case of a wheel motor). This type of sensor limits the speed of the assistance to 25 km/h, which allows the cyclist to comply with the regulations in force;
  • cadence sensor: it allows to moderate the power offered by the assistance by taking into account the number of pedal turns per minute. The sensor is located between the bottom bracket and the crank (in the case of a wheel motor) or in the motor (in the case of a pedal motor);
  • force sensor: which can be mounted at the rear, on the frame, at the level of the derailleur hanger, this type of sensor measures the mechanical torsions determined by the pedaling. This is the basis for the control unit to calculate the power that the motor should deliver. In general, this determines a more natural behavior of the EAB.

The battery

The battery powers the motor. It provides it with the necessary energy to start up and support the cyclist in his pedaling effort. At the beginning of electrically assisted bicycles, at the end of the 90s, the batteries were lead-acid. Technological developments have allowed us to move from Nickel-Cadmium (Ni-Cad) to Nickel Metal Hydride (Ni-Mh) to Lithium Ion (Li-ion) and Lithium polymer. The batteries are now less heavy, but still have a good autonomy. Depending on the electric bike, they can be positioned :

  • on the frame ;
  • on the luggage rack ;
  • inside the frame tubes.

If their location does not affect the electric assistance system, it modifies the behavior and the aesthetics of the bike. Thus, the more the battery is integrated into the shape of the frame, the more the harmony of the electric bike is preserved and its ergonomics reinforced. This has been the trend for most manufacturers for several years. Electric bikes with removable batteries are also very popular. The battery goes into standby mode after a few hours, so the rider has to take it out and put it back in to use the electric assistance again. To recharge the bike, simply plug the battery into the mains via a power cable.

The control console

This is also called the "display" or "selector". It is in fact a small box that allows you to manage the assistance mode and the battery level. The number of assistance levels is on average 3:

  • economic mode: the cyclist benefits from a minimal assistance;
  • intermediate/normal mode: the cyclist benefits from an average assistance;
  • Fast mode: the rider receives high assistance.

The assistance mode to choose depends on the route to be covered. The flatter the terrain, the more assistance the system should provide to support the rider's efforts. However, it is possible to ride without assistance. This is convenient for saving battery power. On high-end models, an LCD screen acts as a control console and provides additional information, including mileage and estimated range based on the level of assistance provided. Placed on the handlebars of the electric bicycle, the console can be fixed or removable. If it is removable, it can also serve as an electronic key. In this case, it is impossible to use the bike without the display.

The controller

An integrated software located in the motor housing, or remote, depending on the type of motor, determines the performance of the electric bicycle. It is the seat of the EAB's intelligence. The controller makes the link between the motor and the battery according to the information sent back by the sensors via the control console. It also regulates the operation of these electrical components. Like an orchestra conductor, it adjusts the power of the motor and manages electrical consumption, as well as other elements, including

  • the reactivity of the assistance ;
  • assistance levels;
  • display parameters;
  • the torque developed by the motor;
  • possible diagnostics.

Quel est le fonctionnement d'un vélo à assistance électrique ?-2

Electric bicycle: mode of use

Theuse of an electric bicycle is subject to a certain number of rules. There is a speed limit to observe when riding in a large city. Indeed, the maximum speed allowed for an eBike is 25 km/h. Thus, there are 3 rules to respect to stay within the legal framework of bicycles.

  1. The assistance must be activated only when pedaling.
  2. The assistance must stop when the speed exceeds 25 km/h.
  3. The electric motor must not exceed 250 watts.

When we talk about the use of the electric bicycle, we also refer to its operation. The modus operandi is simple. The ignition is usually done at the control console. A switch is used to turn on the system. Once powered up, the console lights up, but the motor does not yet start. When the rider starts pedaling, the pedal sensor sends an electrical signal to the controller that starts the battery and motor. This action is calibrated according to the level of assistance indicated by the display and the reading of the signal sent by the sensor.

All this information decrypted by the controller allows it to adjust the power of the motor so that the assistance is more or less natural. The safest system is the one that selects a low level of assistance by default. It is possible to change assistance levels while riding. In this case, simply select the desired level on the dashboard of the machine and that's it. The cyclist can thus alternate at will the moments of effort and relaxation during the whole journey to the destination.

We can conclude that an EAB is not a bike that works by motor propulsion. You have to pedal to activate the assistance.

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