5 minutes to read the essence and working principle of electric vehicles

Although electric cars have been around for many years, they don't quite understand what electric cars are for more ordinary consumers.

First of all, the electric vehicle referred to in this paper refers to a pure battery-driven vehicle, and the more general fuel cell and plug-in hybrid vehicle are not counted. The second point to note is that pure electric vehicles are simply abandoning the powertrain of traditional cars and some supporting components. Nissan Leaf, Tesla Model S, Ford Focus Electric Vehicle, Honda Fit Electric Vehicle, etc., are in fact not much different from traditional cars. They are unique in that they use electric energy instead of internal combustion engines to drive vehicles.

The electric vehicle powertrain includes a battery pack, a controller, and a motor. When developing an electric car, the car company can be retrofitted based on the original traditional model, or it can completely develop a new model.

battery

In fact, there were electric vehicles as early as 100 years ago, but the batteries of electric vehicles were cumbersome, inefficient, and small in capacity, not to mention battery management technology and safety technology.

After decades of development, the popular energy storage system for electric vehicles has changed from lead-acid batteries to lithium batteries. Tesla used nearly 7,000 lithium batteries in its Roadster model launched in 2008. Every car company thinks their lithium battery performance is the best, but in fact, they all use similar rechargeable lithium-ion batteries.

The time required for the battery pack to be fully charged is determined by the battery pack capacity, the charging device power, and the charging current. All electric vehicles have a brake energy recovery function that converts thermal energy into electrical energy to feed back to the battery pack during vehicle deceleration. However, the energy obtained by this approach is negligible for the driving energy required for electric vehicles. It is completely impractical for some companies to boast that the electric vehicle can be turned into a “perpetual motion machine” by means of energy recovery.

In terms of charging, although it can be supplied by a household power grid socket, this is a method of efficiency**. Even the 16 kWh battery pack in the Mitsubishi i-MiEV takes 20 hours to fill, while the Tesla** 85 kWh battery pack with the Model S takes several days.

Of course, users can spend an additional few hundred dollars at home equipped with Electric Vehicle Supply Equipment (EVSE) to make charging more efficient.

The fastest charging method is the DC charging of the shared charging station. The voltage can generally reach 480 volts. Of course, Tesla's super charging station is higher and can be filled with 80% of electricity in 20 minutes.

Today's electric vehicle batteries have a built-in battery management system BMS, which is controlled by software for charging and discharging. The battery management system mainly prevents the battery from being over-discharged, or the battery is over-filled, in order to extend the battery life as much as possible.

In fact, even if the battery energy is "empty", it can still supply a certain amount of current, but this will seriously affect its service life.

In some ways, batteries are like humans – they perform better at the right temperature. Of course, they can work under extremely cold and extremely hot temperatures, but the cruising range they can support is significantly lower than normal. In order to solve such problems, engineers will add an active temperature control system to the battery, usually using liquid cooling. And some car companies are still confident that they do not use temperature control systems, such as the 2015 Volkswagen e-Golf electric car. According to the public, the car's battery uses a more suitable electrochemical material, there is almost no self-heating tendency, so no temperature control system is needed.

Controller

The controller is the brain of an electric vehicle. In the simplest terms, the controller is the bridge that connects the battery energy to the motor that drives the wheels. When the driver steps on the accelerator pedal is the process of operating the controller, the role of the controller is equivalent to the varistor in the dimmable lamp in the home.

In the car, connected to the accelerator pedal, it can change the current output power within a certain range. The current supplied to the motor by the battery is regulated by the controller.

The ** electric vehicle uses an efficient, high-power alternator, and the controller is responsible for converting the direct current in the battery to alternating current.

Motor

The motor responsible for driving the wheels in an electric vehicle is also referred to as a traction motor. AC induction motors and AC permanent magnet motors are currently the most widely used types of motors with high torque, stable operation and light weight.

The stator in the motor generates a magnetic field using the alternating current transmitted from the power system, and the rotor inside the stator is responsible for converting the electrical energy into mechanical energy output.

In addition to acting as a power transmission, the motor can also reverse charge the battery, which is called a "generator." When the electric vehicle is decelerating, the braking energy recovery system transmits the electric energy back to the battery through the electric motor.

One electric vehicle can be equipped with one or more electric motors, and some can be mounted directly inside the wheel by means of a hub motor. After considering the advantages and disadvantages of the hub motor (simplifying the vehicle structure but increasing the quality of the unsprung), there is currently no car manufacturer.

The advantage of motor drive over conventional internal combustion engine drive is that it has higher energy efficiency and can achieve ** torque from the beginning, far exceeding the internal combustion engine in terms of vehicle acceleration performance.

Powertrain structure is simple: no transmission required

For a pure electric vehicle, if a fixed ratio reducer, commonly known as a cancel transmission, is used, the acceleration time and the speed of the vehicle often constrain each other. Therefore, for high-performance pure electric vehicles with high vehicle acceleration performance and high speed, especially pure electric sports cars, when the weight and cost of the motor are limited, it is possible to consider adding a transmission to improve the speed of the vehicle. And shorten the vehicle acceleration time. However, just as the performance of a family car cannot be in accordance with the standards of a sports car, the performance requirements of a pure electric sports car and a pure electric car used for daily travel are also different. In fact, by properly designing the motor characteristic curve and matching the reduction ratio of the reducer, most pure electric vehicles can also be designed for speeds of more than 150 kilometers per hour, which basically meets market demand. Therefore, from a performance point of view, it is not necessary to install a transmission for a pure electric vehicle.

The Tesla Model S achieves a 130 mph ** speed with a fixed reduction ratio of 9.73:1. Of course, the opposite example is also there. The Porsche Panamera S E-Hybrid can be used with an 8-speed manual transmission in pure electric mode.

In any case, electric vehicles have an advantage over conventional internal combustion engines in terms of performance and post-maintenance/repair costs.

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