# Driving range of pure electric vehicles

The mileage that a car travels at a constant speed after a single charge on a good level road surface until it consumes all of the electrical energy it carries is called the continuous mileage of constant speed driving. It is one of the economic indicators of pure electric vehicles.

The rated total energy carried by the battery is

In the formula, E_{m} (W·h) is the rated total energy carried by the battery: C_{m} (Ah) is the rated capacity of the battery; U_{m} (V) is the terminal voltage of the battery; G_{m} (kg) is the total mass of the battery carried by the pure electric vehicle : q (Wh/kg) is the specific energy of the battery.

The driving mileage at a constant speed is

In the formula, S_{d0} (km) is the distance the car travels at a constant speed.

The continuous driving range under multiple working conditions is

In the formula, S (km) is the continuous driving range in multiple working conditions: S_{i} (km) is the distance traveled in each state; k is the total number of states that the vehicle can complete.

The influencing factors of the driving range of pure electric vehicles are more complicated, and the most important factor is the power battery. The driving range is closely related to the energy consumed by a pure electric vehicle during driving. The influencing factors mainly come from the external conditions of the pure electric vehicle and the structural conditions of the pure electric vehicle itself. The following analyzes the impact on the driving range of pure electric vehicles from six main aspects.

1) The influence of rolling resistance coefficient on driving range

The smaller the tire’s rolling resistance coefficient, the longer the driving range. Therefore, reducing the tire rolling resistance coefficient can significantly increase the driving range of pure electric vehicles, especially for low-speed, high-quality pure electric vehicles. Therefore, adopting radial tires with a small rolling resistance coefficient and increasing tire pressure are important ways to increase the driving range of pure electric vehicles.

2) The influence of air resistance coefficient on driving range

The smaller the air resistance coefficient, the longer the driving range. The faster the speed, the more obvious the influence of air resistance coefficient on the driving range of pure electric vehicles. The streamlined design of the pure electric vehicle is made with a smooth surface at the bottom to reduce the protrusion of the body surface. At the same time, measures such as the elimination of the radiator cover can reduce the air resistance coefficient.

3) The influence of mechanical efficiency on driving range

Improving the mechanical efficiency of the power transmission system of pure electric vehicles can effectively increase the driving range of pure electric vehicles. The smaller the mass of the pure electric vehicle, the lower the driving speed, and the greater the impact of mechanical efficiency on the driving range.

4) The impact of vehicle quality on driving range

The greater the quality of the vehicle, the shorter the driving range; and at different speeds, the driving range is also different. In order to reduce the total mass of the vehicle, it can be achieved by using lightweight materials.

5) The influence of battery parameters on driving range

There are many battery parameters, including the depth of discharge of the battery, the specific energy of the battery, the number of batteries in series in the battery box, the number of battery groups in parallel in the battery box, and the self-discharge rate.

(1) Depth of discharge. The greater the depth of discharge of the battery, the longer the driving range of a pure electric vehicle. At the same time, the influence of speed and load on the driving range is also obvious.

(2) Battery specific energy. When the total amount of batteries carried by a pure electric vehicle is constant, the specific energy of the battery in the battery parameters has the greatest impact on the driving range. It can be seen that increasing the specific energy of the battery is of great significance to improving the driving range of the pure electric vehicle.

(3) The number of batteries connected in series in the battery box. Increasing the number of batteries connected in series in each battery box will significantly increase the driving range of pure electric vehicles. This is mainly due to the increase in the number of batteries on the one hand, which can increase the total energy reserve of the battery pack; on the other hand, the increase in the voltage of the battery pack reduces the discharge current of the battery when the battery discharge efficiency is the same. The effective capacity of the battery pack. Although the increase in the number of batteries also increases the total mass of pure electric vehicles, which leads to increased energy consumption of pure electric vehicles and reduces the driving range of pure electric vehicles, the increase in the voltage of the battery pack will increase the power performance of pure electric vehicles. Has been greatly improved. Therefore, the matching of the power transmission system of pure electric vehicles should take into account the range and power of pure electric vehicles.

(4) The number of battery packs connected in parallel in the battery box. While maintaining the total voltage of the battery pack, increasing the number of parallel battery boxes can significantly increase the driving range of pure electric vehicles. This is mainly due to the increase in the number of batteries on the one hand, which can increase the total energy reserve of the battery pack; on the other hand, due to the increase of the parallel branches, the battery pack can be increased when the battery box of each parallel branch does not exceed the rated discharge current. The total discharge current, thereby increasing the rated capacity of the battery pack. Increasing the number of battery boxes in parallel can increase the discharge power of the battery pack, and the power performance of pure electric vehicles will also be significantly improved. Therefore, increasing the number of battery boxes in parallel can improve the power and driving range of pure electric vehicles. However, with the increase in the number of batteries, the proportion of batteries in the mass of the vehicle and the total mass of pure electric vehicles will increase, which will increase the energy consumption of pure electric vehicles and reduce the driving range of pure electric vehicles.

(5) Self-discharge rate. The self-discharge rate of a battery refers to the rate of decrease in capacity during the storage period of the battery, that is, the rate at which the battery discharges itself when there is no load to lose capacity. Obviously, the greater the self-discharge rate, the greater the capacity loss of the battery during storage, the greater the useless loss of energy, and the shorter the driving range of the corresponding pure electric vehicle.

6) The influence of other factors on the driving range

(1) Driving conditions. Driving conditions have a great influence on the driving range of pure electric vehicles. For accelerated driving conditions, the current increases with the increase in speed, the electric energy consumed per kilometer increases with the increase in speed, and the discharge capacity of the battery decreases with the increase in speed, so its driving range varies with driving. The speed increases and decreases.

(2) Driving environment. Under the same vehicle conditions, the road conditions and environmental climate of pure electric vehicles have a great influence on the driving range of pure electric vehicles. For example, the level of ambient temperature has a great influence on the effective capacity of the battery on the one hand; Aspects will also affect the total efficiency of pure electric vehicles (motor efficiency, mechanical transmission efficiency and efficiency of electrical components, etc.) and the energy consumed by ventilation, cooling, and air conditioning. In addition, the direction and size of the wind, the type of road (coefficient of friction, slope, smoothness), and traffic jams will increase or decrease the energy consumption of vehicles, which makes the driving range of pure electric vehicles significantly different.

(3) Auxiliary system and low-voltage electrical system. The air compressor of the braking system and the oil pump of the steering system on a pure electric vehicle need to be driven by an auxiliary motor. Other electrical appliances such as lighting, audio, air conditioning, ventilation, and heating all need to consume battery energy. The greater the power of the auxiliary system and the low-voltage system, the greater the power consumption, the smaller the driving range of the pure electric vehicle, and the power performance will also be affected.

It can be seen that there are many factors that affect the driving range of pure electric vehicles. In the actual design, the influence of various factors should be considered as comprehensively as possible to increase the driving range of pure electric vehicles.