Understand the basics of pure electric vehicles-Xinda Motor- electric motors and EV accessories supplier|INDEX--

Understand the basics of pure electric vehicles

Date：2022-10-10　　　Author：XINDA MOTOR

A pure electric vehicle refers to a vehicle powered by an on-board power supply and driven by an electric motor, which meets the requirements of road traffic and safety regulations, and usually uses a high-efficiency rechargeable battery as the power source. Pure electric vehicles do not need internal combustion engines, so the electric motor of pure electric vehicles is equivalent to the engine of a traditional car, and the battery is equivalent to the original fuel tank.

The basic components of pure electric vehicles

electric motor

The electric motor is the power device of the electric vehicle. It is an electromagnetic device that realizes the conversion of electric energy according to the principle of electromagnetic induction. It is represented by the letter M in the circuit. Its main function is to generate rotational motion as a power source for electrical equipment or various machinery.

dynamo

The main function of the generator is to convert mechanical energy into electrical energy, which is represented by the letter G in the circuit.

cooling system

The cooling system usually consists of a radiator, a water pump, a fan, a thermostat, a coolant temperature gauge and a water drain switch. The electric vehicle engine adopts two cooling methods, namely air cooling and water cooling. Usually, the electric vehicle engine adopts water cooling.

Transmission system

Pure electric vehicle chassis, because its electric motor has good traction characteristics, so the transmission system of battery vehicles does not require clutches and transmissions. The speed control of the vehicle can be realized by changing the speed of the motor through the speed regulation system.

driving system

The driving system is similar to that of a fuel vehicle, mainly including the frame, axle, wheels and suspension. The function of the electric vehicle driving system is to receive the torque transmitted by the motor through the transmission system, and through the adhesion between the driving wheel and the road surface, generate the traction force of the road surface on the electric vehicle to ensure the normal driving of the vehicle. In addition, it should alleviate the shock and vibration caused by uneven road to the body as much as possible to ensure the normal driving of electric vehicles.

steering system

The function of the electric vehicle steering system is to maintain or change the driving direction of the electric vehicle, and it includes components such as a steering control mechanism, a steering gear and a steering transmission mechanism. Steering system consists of steering wheel, steering gear, steering knuckle, steering knuckle arm, tie rod, straight tie rod, etc. When the electric vehicle is steered, it is necessary to ensure that there is a coordinated angular relationship between the steering wheels. By manipulating the steering system, the driver keeps the electric vehicle in a straight line or turning motion state, or converts between the above two motion states; it is also necessary to ensure that the steering wheel does not vibrate, the steering wheel does not swing, and the steering wheel does not vibrate under the driving state. Sensitive, with a small minimum turning diameter and light handling.

Braking System

The braking system is a general term for all braking and deceleration systems equipped with electric vehicles. Its function is to reduce the speed of the electric vehicle in motion or stop it, or to keep the electric vehicle that has been stopped. The braking system includes a brake and a braking transmission device. Anti-lock braking devices are also installed in the braking system of modern electric vehicles. Similar to fuel vehicles, the braking system of pure electric vehicles is also composed of two sets of service brakes and parking brakes.

Electrical Equipment

Electric vehicle electrical equipment mainly includes batteries, generators, lighting fixtures, instruments, audio devices, wipers, etc.

The role of the battery is to supply electricity to the starter and the motor. In order to meet the high voltage demand of electric vehicles, pure electric vehicles usually use a power battery pack formed by multiple 12V or 24V batteries in series and parallel as the power source. The voltage of the power battery pack is 155~400V, which is charged periodically. to replenish power. The power battery pack is the key equipment of the pure electric vehicle. The electric energy it stores and its own weight and volume have a decisive influence on the performance of the pure electric vehicle. The power battery pack occupies a large part of the effective loading space on pure electric vehicles, and it is quite difficult to arrange it. Generally, there are two forms of centralized arrangement and decentralized arrangement. The Delco battery pack used in GM's EV1 adopts a centralized arrangement, and the support for the power battery pack is a T-shaped frame. The T-shaped frame is installed on the frame under the floor of the vehicle and under the trunk. The power battery pack is fixed on the T-shaped frame with good stability. It is installed from the rear of the vehicle. The ventilation system of the power battery pack, the wire protection cover, etc. are installed on the T-frame, and the automatic and manual circuit breakers are used to cut off the power supply when the vehicle is stopped and the vehicle fails to ensure the safety of the high-voltage circuit.

The RAV4EV of Toyota Motor Corporation of Japan is to fix the power battery pack on the frame of the pure electric vehicle. The power battery pack consists of 24 12V nickel-hydrogen batteries with a total voltage of 288V. The power battery group is divided into several "groups", which are distributed on the frame, and then connected in series, so that the effective space on the vehicle chassis can be fully utilized. It is the most common layout method to set the power battery pack under the floor of the pure electric vehicle, which is convenient for installation and removal.

energy recovery system

The function of the energy recovery system is to convert the inertial mechanical energy during coasting into electrical energy when the electric vehicle is coasting (or braking), and store it in the capacitor or charge the power battery, which can quickly release the energy when in use.

cooling system

Because the battery will generate a lot of heat during the operation of the vehicle, having a good heat dissipation system is very important for the safety of the electric vehicle and the life of the battery.

body

The body is divided into two parts, the front and the carriage. The front part of the car can usually take two people, the driver and the co-pilot. The carriage is modified according to customer needs, including carriage configuration, materials, space design, etc. In order to maximize the comfort of passengers, electric vehicles usually adopt a single-seat side-by-side approach, and the number of seats varies according to the specific model.

industrial installation

Industrial devices are specially arranged for industrial pure electric vehicles to complete the operation requirements, such as lifting devices, gantry, forks, etc. of electric forklifts. The lifting of the fork and the tilting of the mast are generally completed by a hydraulic system driven by an electric motor.

Types of pure electric vehicles

Single battery as power source

For pure electric vehicles using a single battery as the power source, only a battery pack is installed.

Equipped with auxiliary power source

For pure electric vehicles using a single battery as the power source, the specific energy and specific power of the battery are low, and the weight and volume of the battery pack are large. Therefore, auxiliary power sources, such as supercapacitors, generator sets, solar energy, etc., are added to some pure electric vehicles, thereby improving the starting performance of pure electric vehicles and increasing the driving range.

How Pure Electric Vehicles Work

A pure electric vehicle uses the energy of the battery to make the electric motor drive the wheels forward. Energy flow route: battery → power conditioner → electric motor → powertrain → drive wheel . Among them, the battery provides current, which is output to the electric motor after passing through the power conditioner, and then the electric motor provides torque, and drives the wheels through the transmission device to realize the running of the vehicle.

Classification of pure electric vehicles

Classification by drive system composition and arrangement

mechanical transmission

The mechanical transmission type pure electric vehicle is developed on the basis of the structure of the front and rear-wheel drive of the engine of the fuel vehicle, and the transmission system of the internal combustion engine vehicle is retained. The difference is that the internal combustion engine is replaced by an electric motor. This structure can ensure the starting torque of the pure electric vehicle and the backup power at low speed, and has low requirements on the drive motor, so a motor with a lower power can be selected.

C—clutch; D—differential; FG—fixed ratio reducer; GB—transmission; M—motor

Transmissionless

A structure of a pure electric vehicle without transmission is shown in the figure. The biggest feature of this structure is that the clutch and transmission are cancelled, and a fixed speed ratio reducer is used to realize the speed change function by controlling the electric motor. The advantage of this structure is that the mechanical transmission device is light in weight and small in size, but the requirements for the motor are relatively high, not only requiring high starting torque, but also requiring large backup power to ensure the starting of pure electric vehicles. , climbing, acceleration and other dynamic performance.

Another structure of a pure electric vehicle without a transmission is shown in the figure, which is similar to the layout of the engine laterally forward and the front-wheel drive of a traditional fuel vehicle. It integrates the electric motor, the fixed ratio reducer and the differential into a whole, and the two half shafts connect the driving wheels. This structure is very common in small electric vehicles.

Differential type

Differential-free pure electric vehicles use two electric motors, which drive the two wheels respectively through a fixed ratio reducer, which can realize the independent adjustment of the speed of each electric motor. Therefore, when the car turns, the differential speed of the two wheels can be controlled by the electronic control system of the electric motor, so as to achieve the purpose of turning. However, the motor control system of this structure is relatively complicated.

Electric wheel type

A structure of an electric wheel-type pure electric vehicle is shown in the figure. In this structure, the electric motor is directly installed in the driving wheel (also called in-wheel motor), which can further shorten the power transmission path between the electric motor and the driving wheel. Energy is lost on the transmission path, but in order to achieve the normal operation of pure electric vehicles, it is necessary to add a planetary gear reducer with a relatively large reduction to reduce the speed of the motor to the ideal wheel speed.

Another structure of the electric wheel type pure electric vehicle is shown in the figure. In this structure, the outer rotor of the low-speed outer rotor motor is directly installed on the rim of the wheel, and the reduction gear is removed. There is no mechanical transmission device, no mechanical transmission loss, high energy transfer efficiency, and large space utilization. However, this structure has high requirements on the performance of the electric motor, and requires it to have a high starting torque and a large backup power to ensure the reliable operation of the vehicle.

Classification according to the number of vehicle power supplies

single power supply

In single-source pure electric vehicles, the main power source is usually batteries, such as lead-acid batteries, nickel-hydrogen batteries, lithium-ion batteries , etc. The structure of the single-power pure electric vehicle is relatively simple, and the control is not difficult. Its main disadvantage is that the instantaneous output power of the main power supply is easily affected by the performance of the battery, and the feedback efficiency of the vehicle braking energy is also limited by the maximum acceptable current of the battery. The state of charge of the battery.

Multiple power sources

A multi-power pure electric vehicle is usually composed of a battery and an energy storage device . The power supply combination of battery plus super capacitor or battery plus flywheel battery can reduce the requirements for battery capacity, specific energy, specific power, etc. When the car starts, accelerates, and climbs a hill, the auxiliary energy storage device (super capacitor, flywheel battery) can output high power in a short time, assist the battery to supply power, and improve the power performance of the electric vehicle; when the car brakes, use the auxiliary power The energy storage device accepts high current charging to increase the efficiency of braking energy feedback.

Key Technologies of Pure Electric Vehicles

Battery and Management Technology

The battery is the power source of electric vehicles, and it is also a key factor restricting the development of electric vehicles. To make electric vehicles competitive with fuel vehicles, the key is to develop high-efficiency batteries with high specific energy, high specific power, long service life and low cost. But at present, there is no battery that can meet the requirements of the popularization of pure electric vehicles. The performance of the battery pack directly affects the acceleration performance, driving range and efficiency of braking energy recovery of the vehicle . The cost and cycle life of a battery directly affects the cost and reliability of a vehicle, and all parameters that affect battery performance must be optimized. The battery of an electric vehicle generates a large amount of heat during use, and the battery temperature affects the operation, cycle life, charging acceptability, power and energy, safety and reliability of the battery's electrochemical system. Therefore, in order to achieve the best performance and life, it is necessary to control the temperature of the battery pack within a certain range to reduce the uneven temperature distribution in the battery pack, so as to avoid the imbalance between modules, so as to prevent the battery performance from deteriorating, and to reduce the uneven temperature distribution in the battery pack. Eliminate the associated potential hazards.

Vehicle control technology

The whole vehicle control system of the new pure electric vehicle is a network structure of two buses, namely the high-speed CAN bus of the drive system and the low-speed bus of the body system . Each node of the high-speed CAN bus is the ECU of each subsystem, and the low-speed bus sets the nodes according to the physical location. The basic principle is the regional autonomy based on the spatial location. The significance of realizing the networked control of the whole vehicle is not only to solve the problems of complex lines and increased wiring harnesses in the automotive electronics, but also to realize the communication and resource sharing capabilities realized by the network. It also provides strong support for X-by-Wire technology.

Vehicle lightweight technology

Vehicle lightweight technology has always been an important research content in automotive technology. Due to the battery pack of pure electric vehicles, the weight of the whole vehicle increases a lot, and the lightweight problem is more significant. The following measures can be taken to reduce the weight of the whole vehicle.

① Through the analysis of the actual use conditions and use requirements of the whole vehicle, the overall optimization of vehicle parameters such as battery voltage, capacity, drive motor power, speed and torque, and vehicle performance , and rational selection of battery and motor parameters.

②Through structural optimization and integrated and modular optimization design, the weight of powertrain and vehicle-mounted energy system can be reduced. This includes the integration and modular design of the electric motor and drive, transmission system, cooling system, air conditioning and brake vacuum system to optimize the system; Reasonable integration and decentralization to achieve system optimization.

③ Actively select lightweight materials , such as the structural frame of the battery box, the box cover, the wheel hub, etc., using lightweight alloy materials.

④Use CAD technology to carry out finite element analysis and research on the body load-bearing structural parts (such as front and rear axles, newly added side beams, cross beams, etc.), and achieve structural optimization by combining calculation and testing .

Understand the basics of pure electric vehicles

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