Basic structure of pure electric vehicle

Basic structure of pure electric vehicle

Compared with traditional cars, pure electric vehicles have the same body, on-board electrical system and some basic hydraulic braking and steering components. However, pure electric vehicles also have many unique structural components, including drive system, on-board 12V power supply system and external charging system. The figure shows the structural layout of a typical pure electric vehicle.

1) power battery

Power battery, also known as power battery, high-voltage power battery or high-voltage battery. Used to store electrical energy. At present, the power batteries of pure electric vehicles in the market mainly use lithium batteries, including lithium iron phosphate batteries, lithium cobalt oxide batteries and ternary lithium batteries, which can realize the cyclic charging and discharging of batteries. Because pure electric vehicles need batteries with larger storage capacity, according to the current lithium battery technology, the volume of batteries will increase accordingly. Therefore, at present, most of the high-voltage battery packs of pure electric vehicles are installed under the car, which will not occupy too much space in the passenger compartment. ?

The power battery is usually composed of a plurality of single cells connected in series and parallel, and the power battery in the figure is composed of eight battery modules connected in series. For example, Roewe E50 power battery contains five battery modules, of which three large battery modules are respectively connected in series by 27 batteries, and two small battery modules are respectively connected in series by 6 batteries, thus forming 93 series-connected lithium battery cells, and the output voltage is about 300 V. ..

Although the voltage of each battery cell is only about 3.7V, the capacity and voltage of the whole battery pack are further increased by connecting a plurality of battery cells in parallel and then in series.

The following terms are commonly used to describe the internal structural components of power batteries:

(1) battery unit: the smallest unit that constitutes a power battery, generally consisting of a positive electrode, a negative electrode, an electrolyte and a casing, which is what we often call a battery.

(2) Battery cell group: a group of battery cells connected in parallel, whose rated voltage is equal to the rated voltage of battery cells, which is the smallest grouping of battery cells connected in physical structure and circuit.

(3) Battery module: an assembly consisting of a plurality of battery cells or a single battery connected in series.

2) Transmission device with motor

The transmission unit is the power output part of pure electric vehicle, which mainly includes three-phase motor and reduction gear mechanism. If it is a front-wheel vehicle, the system components are generally installed in the front engine room.

Fig. 5 shows the structure of a typical electric vehicle drive motor assembly, in which the motor for driving and the gear mechanism connecting the rotor of the motor can be seen. In addition, the more obvious sign is that there are three high-voltage cables connected to the frequency converter above the speed change unit.

Motor is an important core component of transmission device, which is used for mutual conversion between electrical energy and mechanical energy. At present, pure electric vehicles mostly use three-phase motors, and three-phase permanent magnet synchronous motors are the most widely used.

The stator of a motor is usually a part wound with a three-phase coil, which is fixed with the casing of the speed change unit.

The motor rotor generally adopts permanent magnet structure, which is connected with the output gear mechanism of the speed change unit and is the rotating output part.

3) Inverter

Frequency converter is the main control part of the transmission unit, usually located in the upper part of the motor transmission unit. As shown in the figure, it is the inverter part when the front cabin cover of Roewe E50 pure electric vehicle is opened.

One end of the inverter is electrically connected with the high voltage from the power battery, and the other end is connected with three AC cables driving the motor unit. It is mainly used to convert the direct current from the power battery into three alternating currents to drive the motor. At the same time, when the braking energy is recovered, the alternating current generated by the motor is also converted into direct current and fed back to the power battery.

Most vehicles integrate the inverter with the control module to realize the function of the inverter and manage the operation of the motor, as shown in the figure, the inverter position of BMW I3 pure electric vehicle.

4) Vehicle charger and charging interface

The system usually uses an external 220V AC power supply to enter the vehicle charger through the charging interface, and then the vehicle charger converts the 220V AC power into a DC voltage charged by the power battery pack and provides it to the power battery.

5)DC/DC converter

DC/DC converter is used in vehicle 12V power supply system, usually installed in engine compartment or luggage compartment.

It is used to convert the high-voltage DC of the power battery into the low-voltage DC of 12V, and provide it to the low-voltage electrical equipment on the vehicle, such as charging the 12V battery and supplying power to headlights and interior lights.

The cables connecting high-voltage electrical components of pure electric vehicles belong to high-voltage cables, that is, the above-mentioned high-voltage lines.

The color of the cable outer insulation layer is standard orange. The connectors between high-voltage cables need to meet the national safety standards of high-voltage electrical appliances. At the same time, due to the large current between high-voltage components, the diameter of cables used is above 5 mm