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1. Purpose and scope

An electric bike іs a modern and promising form of urban transport [1]. One of the undeniable advantages of an electric bike is its unlimited choice in bicycle models that can easily be made electric. A ready-made electric bike is a mobile vehicle and in technical characteristics it is not inferior to gas mopeds in any way, but surpasses it by economic benefits at times. All one kilometer on an electric bike costs less than half a penny. On an electric bike, you can get to school or work without any difficulty.

Driving a bike absolutely does not require a driver’s license. An electric bike is not subject to registration with the traffic police.

2. Overview of approaches to the implementation of electric bicycles

An electric bike is an electric drive bike that partially or fully provides its movement. An electric bike differs from the usual one by the presence of three additional components: an electric motor, a battery and a controller with a display. Unlike an electric scooter or an electric motorcycle, an electric bicycle can be driven by pedals, for example, when the battery is discharged, and its maintenance and operation is a little more complicated compared to a conventional bicycle.

Electric bikes are not much different from regular bikes. The main difference is the physical effort that the owner needs to make. In simple words, if a person is tired of pedaling, an electric drive begins to perform this work for him. Thanks to this device, the bike can move to moped mode and can travel distances of several tens of kilometers without special efforts. There are special torque sensors (pedal assist), which, when the pedals are twisted, send signals to the controller, thereby starting the electric motor, which greatly facilitates the efforts of the cyclist.

Today, the advantages of electric bicycles compared to urban public and private transport are becoming more apparent. Many people, in big cities, wanting to save time on travel and avoid long traffic jams, refuse public transport and transfer to bicycles.

But not every adult is able to travel long distances by bicycle. And it is precisely such people who most often choose electric bikes. At the moment, a steady increase in sales of electric bikes is becoming apparent that these bikes have a future. The popularity of electric bicycles is also made possible by the fact that to manage them there is almost no need to obtain any permits or have a driver’s license, although owners of powerful electric motors still need to have a document confirming the electric motor’s power.

Main advantages:

Imperfections of existing designs:

3. General description of the hardware of the electric bike

In general, electric bikes can be divided into:

The most common version of a bicycle electric drive based on a brushless DC motor (fan motor). The engine is installed in the wheel instead of the hub on both the front and rear wheels (Figure 1.1). The use of a motor-wheel makes it possible to re-equip almost any common city bike with an electric drive at minimal cost, and its design is almost not violated. The motor wheel can be either one of the wheels (front or rear), or both at the same time. Often the motor-wheel is sold in an already assembled (spoke) form. All motor wheels are mounted on a rim with only 36 spoke holes. The power range of mass-produced motor wheels that drive electric bicycles, as a rule, ranges from 250 to 5000 watts.

There are two types of motor wheels: gear and gearless. In the case of the gear motor wheel there is a motor with a high speed and low torque, which is more compact, lightweight, cheap and technologically advanced due to the low stator magnetic induction, a planetary gearbox and an overrunning clutch. The freewheel clutch of the gear motor wheels, on the one hand, facilitates movement by driver force or coasting at times when an external action rotates the wheel faster than the engine does, the motor behaves like a plain bearing. But on the other hand, the same effect, in contrast to the direct engine, makes it impossible to recover the energy of an electric bike. Plastic (polycarbonate) gears of the planetary gearbox are made to reduce the noise and weight of the motor-wheel, however, they do not have a large margin of safety, unlike metal ones. These gears also reduce wear on the motor shaft and overrunning clutch.

Motor wheel

Figure 1.1 – Motor wheel

3.1 Gearless wheel

A gearless wheel (forward wheel) is a low-speed engine with a large torque, the rotation of which is transmitted directly to the wheel, which simplifies the design and increases reliability [7]. However, to obtain an engine with the necessary characteristics of the frequency and torque, a very strong magnetic field is required in its stator, therefore gearless motor wheels have large dimensions and engine weight due to the massive rare-earth permanent neodymium magnets in the stator.

The forward engine does not have a gearbox and an overrunning clutch with gears, so the engine always rotates. On the one hand, this allows the use of regenerative braking, but on the other hand, even if the motor windings are completely disconnected from the electric circuit, there are noticeable eddy current losses in it, which worsen the speed and make it difficult to pedal.

Advantages of using a motor wheel:

The disadvantages include:

3.2 Outboard motor

Outboard motor - an electric drive option is more efficient than a motor-wheel, but also more expensive. With less weight and power, chain-driven e-bikes reach higher speeds. Often, engines used in any household or automotive equipment, for example, an electric motor from a drill, are used to modify bicycles (Figure 1.2).

Outboard motor

Figure 1.2 – Outboard motor

The power range, as a rule, ranges from 250 to 3000 W; a set of a 3 kW motor can accelerate an electric bike to 100 km / h.

The advantages of a chain electric drive include:

The disadvantages include:

A less common, ineffective scheme, in which the electric motor is mounted above the wheel (usually the rear) and transfers torque from the engine shaft directly to the tire cover (Figure 1.3). There are options for installing a Bulgarian electric motor without a cutting disc. When turning on such an engine, it is advisable to connect the motor to the wheel in advance in order to avoid rapid tire wear. Such motors are usually powered by a 220 V network, which means that in addition to the battery, it is necessary to have an inverter for sufficient power. This option significantly reduces the efficiency of the entire installation.

Friction drive

Figure 1.3 – Friction drive

The only plus:

Disadvantages:

3.3 Electric carriage

Carriage electric drive (Mid Drive) [6] is the same less common type (mainly due to price), it is based on the transfer of mechanical energy directly to the axis of the carriage, one of the most hidden and invisible types (Figure 1.4).

Such an electric drive has a very powerful torque, because inside the drive there are three gear gears, one of which is made of polycarbonate. The use of a polycarbonate gear reduces the noise emitted by the motor and slightly reduces weight, but it erases faster and requires special silicone grease.

The most popular manufacturer of this type of motor is Bafang (8fun). This manufacturer also produces motor wheels of various sizes and power.

Carriage electric drive

Figure 1.4 – Carriage electric drive

Advantages:

Disadvantages:

Before buying or assembling an electric bike, everyone wants to know which type of battery to choose. The mileage, price and weight of the electric bike will depend on this choice.

Currently, three types of batteries are used:

4. Lead acid (SLA) and helium batteries.

The cheapest and most common, but have a small resource and heavy weight. A 36 V battery with a capacity of 8 A * hour weighs about 10 kg with a resource of about 300 charge-discharge cycles [3, 4]. If the battery operates in nominal mode, then the capacity loss is not large, but a short-term overload can lead to a significant loss of capacity (50-80%). Also, this type of battery is very afraid of deep discharge. The main reasons for the decrease in capacity is the chemical process in the battery itself due to the large current consumption (when the bicycle moves uphill or when starting).

СIt should be noted - helium batteries are less sensitive to deep discharge than lead-acid ones. It is necessary to carefully monitor the recommended operating mode of these types of batteries.

These types of batteries are significantly inferior to lithium batteries [2].

5. Lithium-ion batteries (Li-ion).

Lithium-ion batteries are the best power sources of current [5]. The advantages of Li-ion batteries are a large number of cycles, high energy density and low self-discharge. The technology of their production is constantly being improved, and the cost is reduced. The specific gravity of stored energy is constantly growing.

The lithium-ion battery consists of positive and negative electrodes, an electrolyte, a porous separator and contacts. For negative plates, graphite is used. As the cathode material, several materials are used:

The chemical composition of the cathode material used largely determines the technical characteristics of the batteries.

All batteries are subject to degradation in time and on the number of charge-discharge cycles. Battery operation at discharge currents above the nominal capacity, as a rule, leads to a significant decrease in battery life due to an increase in the internal temperature of cells during operation at high currents. Degradation is determined to a large extent by the temperature of operation and storage, and accelerates with increasing temperature.

Lithium iron phosphate batteries (LiFePo4) are less prone to degradation than all other lithium batteries.

It should be noted that lithium-ion batteries have the property of spontaneous combustion. The self-ignition of such a battery is difficult to extinguish, not only due to the release of stored electrical energy, but also because of a number of chemical reactions that release energy for self-heating, therefore such a battery can burn without oxygen. In addition, lithium interacting with water forms a combustible gas - hydrogen, quenching with water is possible only with a low lithium content in the battery. But in general, quenching a lithium battery is inefficient.

General view of electric bicycles

Figure 1.5 – General view of electric bicycles

(animation: 12 shots, 5 cycles, 521 kBytes)

List of sources

  1. Wikipedia [Электронный ресурс]. – Режим доступа: https://ru.wikipedia.org/wiki/Электрический_велосипед.
  2. Выбор аккумулятора для электро-велосипеда[Электронный ресурс]. – Режим доступа: https://lifepo4.by/akkumulyatory-dlya.
  3. Свинцово кислотные аккумуляторы [Электронный ресурс]. – Режим доступа: https://pulsar.kiev.ua/vrla_akkumulyatory.
  4. Свинцово кислотные аккумуляторы выбор [Электронный ресурс]. – Режим доступа: http://alternatenergy.ru.
  5. Li-iOn аккумуляторы [Электронный ресурс]. – Режим доступа: https://habr.com/ru/post/150661/.
  6. Mid Drive [Электронный ресурс]. – Режим доступа: https://electric-biking.com/bafang-8fun-mid-drive-kit-review/.
  7. Мотор прямого хода [Электронный ресурс]. – Режим доступа: http://motor4koleso.ru/stati-i-obzory/11-kak-vybrat-motor-koleso-dlya-elektrovelosipeda.