Pure electric new energy vehicles refer to vehicles that use on-board power as power, use electric motors to drive wheels, and meet the requirements of road traffic and safety regulations. They usually use high-efficiency rechargeable batteries as power sources. Pure electric new energy vehicles do not need internal combustion engines, so the electric motor of pure electric vehicles is equivalent to the engine of traditional vehicles, and the battery is equivalent to the original fuel tank. Electric energy belongs to secondary energy and can come from wind energy, water energy, thermal energy, solar energy, etc.
I. Basic components of pure electric vehicles
01 Motor
The motor is the power device of electric vehicles. It is an electromagnetic device that realizes electric energy conversion based on 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 machines.
02 Generator
The main function of the generator is to convert mechanical energy into electrical energy. It is represented by the letter G in the circuit.
03 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. Electric vehicle engines use two cooling methods, namely air cooling and water cooling. Usually, electric vehicle engines are mostly cooled by water.
04 Transmission system
The chassis of pure electric vehicles, because their motors have good traction characteristics, the transmission system of battery vehicles does not require clutches and transmissions. Vehicle speed control can be achieved by the controller changing the speed of the motor through the speed control system.
05 Driving system
The driving system is similar to that of fuel vehicles, 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 generate traction on the electric vehicle through the adhesion between the drive wheel and the road surface to ensure the normal driving of the whole vehicle. In addition, it should alleviate the impact and vibration caused by uneven roads on the vehicle body as much as possible to ensure the normal driving of the electric vehicle.
06 Steering system
The function of the electric vehicle steering system is to maintain or change the driving direction of the electric vehicle. It includes components such as steering control mechanism, steering gear and steering transmission mechanism. The steering system consists of a steering wheel, steering gear, steering knuckle, steering knuckle arm, tie rod, straight tie rod, etc. When the electric vehicle is turning, it is necessary to ensure that there is a coordinated angle relationship between the steering wheels. The driver controls the steering system to keep the electric vehicle in a straight or turning motion state, or to switch between the two motion states mentioned above; it is also necessary to ensure that the steering wheel does not vibrate, the steering wheel does not swing, the steering is sensitive, the minimum turning diameter is small, and the operation is easy.
07 Braking system
The braking system is the general term for all braking and deceleration systems equipped in electric vehicles. Its function is to reduce the speed or stop the electric vehicle in motion, or to keep the electric vehicle that has stopped moving. The braking system includes brakes and brake transmission devices. Modern electric vehicles also have anti-lock braking devices installed in their braking systems. Similar to fuel vehicles, the braking system of pure electric vehicles also consists of two sets of devices: driving brakes and parking brakes.
08 Electrical equipment
The electrical equipment of electric vehicles mainly includes batteries, generators, lighting fixtures, instruments, audio devices, wipers, etc. The function of the battery is to supply electricity to the starter and 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, and the power is replenished by periodic charging. The power battery pack is a key equipment of pure electric vehicles. The power energy it stores and its own weight and volume have a decisive influence on the performance of pure electric vehicles. 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 General Motors’ EV1 adopts a centralized arrangement form, and the bracket of the power battery pack is a T-shaped frame. The T-shaped frame is installed under the floor of the vehicle and on the frame under the trunk. The power battery pack is fixed on the T-shaped frame and has good stability. It is installed from the rear of the vehicle. The ventilation system, wire protection cover, etc. of the power battery pack are installed on the T-shaped frame. Automatic and manual circuit breakers are used to cut off the power supply when the vehicle stops or the vehicle fails to ensure the safety of the high-voltage circuit.
The RAV4EV of Toyota Motor Corporation of Japan fixes the power battery pack on the frame of the pure electric vehicle with a bracket. The power battery pack consists of 24 12V nickel-hydrogen batteries with a total voltage of 288V. The power battery pack is divided into several “small groups” and arranged on the frame in a dispersed manner, and then connected in series, so that the effective space on the vehicle chassis can be fully utilized. The most common arrangement method is to set the power battery pack under the floor of the pure electric vehicle, which is convenient for installation and removal.
09 Energy recovery system
The function of the energy recovery system is to convert the inertial mechanical energy during the sliding (or braking) of the electric vehicle into electrical energy, and store it in a capacitor or charge the power battery, and release the energy quickly when it is used.
10 Cooling system
Because the battery will generate a lot of heat during the operation of the vehicle, having a good cooling system is crucial to the safety of the electric vehicle and the life of its battery.
11 Body
The body is divided into two parts: the front and the compartment. The front part usually can accommodate the driver and the co-driver. 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 method, and the number of seats varies according to the specific model.
12 Industrial devices
Industrial devices are specially arranged for industrial pure electric vehicles to complete work requirements, such as the lifting device, gantry, and cargo fork of electric forklifts. The lifting of the cargo fork and the tilting of the gantry are generally completed by a hydraulic system driven by an electric motor.
II. Types of pure electric vehicles
01 Single battery as a power source
Pure electric vehicles using a single battery as a power source only have a battery pack installed.
02 Equipped with an auxiliary power source
Pure electric vehicles using a single battery as a power source have lower specific energy and specific power of the battery, and the weight and volume of the battery pack are larger. Therefore, auxiliary power sources are added to some pure electric vehicles, such as supercapacitors, generator sets, solar energy, etc., to improve the starting performance of pure electric vehicles and increase the driving range.
Working principle of pure electric vehicles
Pure electric vehicles use the energy of the battery to drive the wheels forward. Energy flow route: battery → power conditioner → motor → power transmission system → drive wheel. Among them, the battery provides current, which is output to the motor after passing through the power conditioner, and then the motor provides torque, which drives the wheels after passing through the transmission device to realize the vehicle’s travel.
III. Classification of pure electric vehicles
01. Classification by drive system composition and layout
(1) Mechanical transmission type
Mechanical transmission pure electric vehicles are developed based on the structure of fuel vehicles with front engine and rear wheel drive. The transmission system of internal combustion engine vehicles is retained, but the difference is that the internal combustion engine is replaced by an electric motor. This structure can ensure the starting torque and backup power of pure electric vehicles at low speeds, and has low requirements for the drive motor, so a motor with smaller power can be selected.
C—clutch; D—differential; FG—fixed speed ratio reducer; GB—transmission; M—motor
(2) Transmissionless type
A structure of a transmissionless pure electric vehicle is shown in the figure. The biggest feature of this structure is that the clutch and transmission are eliminated, and a fixed speed ratio reducer is used to achieve the speed change function by controlling the motor. The advantage of this structure is that the mechanical transmission device is light and small in size, but the requirements for the motor are relatively high. It not only requires a high starting torque, but also requires a large backup power to ensure the starting, climbing, acceleration and other dynamic performance of the pure electric vehicle. Another structure of a transmission-free pure electric vehicle is shown in the figure. This structure is similar to the layout of the traditional fuel vehicle with the engine placed transversely in front and the front wheels driven. It integrates the motor, fixed speed ratio reducer and differential into a whole, and two half shafts are connected to the drive wheels. This structure is very common in small electric vehicles.
(3) Non-differential type
The non-differential pure electric vehicle uses two motors to drive the two wheels separately through a fixed speed ratio reducer, which can achieve independent adjustment of the speed of each motor. Therefore, when the car turns, the differential of the two wheels can be controlled by the electronic control system of the motor to achieve the purpose of turning. However, the motor control system of this structure is relatively complex.
(4) Electric wheel type
One structure of electric wheel type pure electric vehicle is shown in the figure. This structure is to install the motor directly in the drive wheel (also called wheel hub motor), which can further shorten the power transmission path between the motor and the drive wheel and reduce the energy loss in the transmission path. However, in order to achieve the normal operation of the pure electric vehicle, it is necessary to add a planetary gear reducer with a large reduction ratio to reduce the motor speed to the ideal wheel speed.
Another structure of electric wheel type pure electric vehicle is shown in the figure. This structure installs the outer rotor of the low-speed outer rotor motor directly on the wheel rim and removes the reduction gear. Therefore, there is no mechanical transmission device between the motor and the vehicle’s drive wheel, no mechanical transmission loss, high energy transmission efficiency, and large space utilization. However, this structure has high performance requirements for the motor, requiring it to have a high starting torque and a large backup power to ensure the reliable operation of the vehicle.
02 Classification by the number of on-board power sources
(1) Single power source
In a single-power pure electric vehicle, its main power source is usually a battery, such as a lead-acid battery, a nickel-hydrogen battery, a lithium-ion battery, etc. The structure of a single-power pure electric vehicle is relatively simple and easy to control. Its main disadvantage is that the instantaneous output power of the main power source is easily affected by the performance of the battery, and the feedback efficiency of the vehicle’s braking energy is also subject to the maximum acceptable current of the battery and the battery’s state of charge.
(2) Multi-power sources
Multi-power pure electric vehicles are usually composed of batteries and energy storage devices. The use of a power supply combination of batteries plus supercapacitors or batteries plus flywheel batteries can reduce the requirements for the capacity, specific energy, specific power, etc. of the battery. When the car starts, accelerates, or climbs a slope, the auxiliary energy storage device (supercapacitor, flywheel battery) can output high power in a short period of time to assist the battery in power supply, thereby improving the power of the electric vehicle; when the car brakes, the auxiliary energy storage device is used to receive high current charging to increase the efficiency of braking energy feedback.
IV. Key technologies of pure electric vehicles
01 Battery and management technology
Batteries are the power source of electric vehicles and have always been a key factor restricting the development of electric vehicles. If you want electric vehicles to compete with fuel vehicles, the key is to develop high-efficiency batteries with high specific energy, high specific power, long service life, and low cost. However, no battery 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 brake energy recovery of the whole vehicle. The cost and cycle life of the battery directly affect the cost and reliability of the vehicle, and all parameters affecting the battery performance must be optimized. The battery of an electric vehicle generates a lot of heat during use, and the battery temperature affects the operation of the battery’s electrochemical system, cycle life, charging acceptability, power and energy, safety and reliability. Therefore, in order to achieve the best performance and life, the temperature of the battery pack must be controlled within a certain range to reduce the uneven temperature distribution in the battery pack to avoid imbalance between modules, thereby preventing battery performance from deteriorating and eliminating related potential dangers.
02 Vehicle control technology
The new pure electric vehicle vehicle control system 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 nodes according to the physical location. The basic principle is regional autonomy based on spatial location. The significance of realizing vehicle network control is not only to solve the problems of complex lines and increased wiring harnesses in automobile electronics, but also the communication and resource sharing capabilities realized by networking have become a basis for the application of new electronic and computer technologies in automobiles, and also provide strong support for X-by-Wire technology.
03 Vehicle lightweight technology
Vehicle lightweight technology has always been an important research content of automobile technology. Pure electric vehicles have a large increase in vehicle weight due to the battery pack, and the lightweight problem is more significant. The following measures can be taken to reduce the weight of the vehicle. ① Through the analysis of the actual use conditions and use requirements of the vehicle, the overall optimization of vehicle parameters such as battery voltage, capacity, drive motor power, speed and torque, and vehicle performance, and the reasonable selection of battery and motor parameters. ② Reduce the weight of the powertrain and on-board energy system through structural optimization and integrated and modularized optimization design. This includes the integration and modular design of motors and drives, transmission systems, cooling systems, air conditioning and brake vacuum systems to optimize the system; through the reasonable integration and dispersion of the on-board energy system composed of batteries, battery boxes, battery management systems, and on-board chargers, the system is optimized. ③ Actively select lightweight materials, such as lightweight alloy materials for the battery box’s structural frame, box cover, wheel hub, etc. ④ Use CAD technology to conduct finite element analysis and research on the body’s 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 experiment.
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