I. Technical overview
Electric vehicle refers to a vehicle that is powered by on-board power supply and driven by motor and meets the requirements of road traffic and safety regulations. It is driven by the electricity stored in the battery. Sometimes 12 or 24 batteries are used for driving, and sometimes more is needed.
1, technical characteristics of electric vehicles
● No pollution and low noise.
The exhaust gas produced by electric vehicles without internal combustion engines does not produce tail gas pollution, which is very beneficial to environmental protection and air purification, and is almost "zero pollution". As we all know, CO, HC, NOX, particulate matter, odor and other pollutants in automobile exhaust of internal combustion engines form acid rain, acid fog and photochemical smog. Electric cars have no noise generated by internal combustion engines, and the noise of motors is also smaller than that of internal combustion engines. Noise is also harmful to people's hearing, nerves, cardiovascular system, digestion, endocrine and immune system.
● Energy efficiency and diversification
The research on electric vehicles shows that their energy efficiency has surpassed that of gasoline-powered vehicles. Especially in cities, cars stop and go, and the driving speed is not high, so electric cars are more suitable. The electric car stops and does not consume electricity. During the braking process, the motor can be automatically converted into a generator, and the energy can be reused during braking deceleration. Studies have shown that the same crude oil, after rough refining, is sent to a power plant to generate electricity, and then charged into a battery-driven car. Its energy utilization efficiency is higher than that of refined gasoline and then driven by a gasoline engine, so it is conducive to saving energy and reducing carbon dioxide emissions.
On the other hand, the application of electric vehicles can effectively reduce the dependence on oil resources, and the limited oil can be used in more important aspects. The electricity charged into the battery can be converted from coal, natural gas, hydropower, nuclear energy, solar energy, wind power, tides and other energy sources. In addition, if the battery is charged at night, it can avoid the peak of electricity consumption, which is beneficial to balance the power grid load and reduce the cost.
● Simple structure and convenient use and maintenance.
Compared with internal combustion engine vehicles, electric vehicles have simpler structure, fewer running and transmission parts and less maintenance workload. When using AC induction motor, the motor does not need maintenance, and more importantly, the electric vehicle is easy to operate.
● High cost of power supply and short driving range.
At present, the technology of electric vehicles is not as perfect as that of diesel locomotives, especially the short life of power supply (battery) and high use cost. The storage capacity of the battery is small, the mileage after one charge is not ideal, and the price of electric vehicles is relatively expensive. However, from the perspective of development, with the progress of science and technology, the problem of electric vehicles will be gradually solved by investing corresponding manpower and material resources. Make full use of strengths and avoid weaknesses, electric vehicles will gradually become popular, and its price and use cost will inevitably decrease.
2. Basic structure of electric vehicle
The composition of electric vehicle includes electric drive and control system, driving force transmission and other mechanical systems, as well as working devices to complete established tasks. Electric drive and control system is the core of electric vehicle, and it is also the biggest difference from internal combustion engine vehicle. The electric drive and control system consists of driving motor, power supply and motor speed regulating device. Other devices of electric vehicles are basically the same as internal combustion engines.
2. 1. power supply
The power supply provides electric energy for the driving motor of the electric vehicle, and the motor converts the electric energy of the power supply into mechanical energy, and drives the wheels and working devices through the transmission device or directly. At present, lead-acid battery is the most widely used power supply in electric vehicles, but with the development of electric vehicle technology, many new batteries are also under development. These power sources (batteries) mainly include sodium-sulfur batteries, nickel-chromium batteries, lithium batteries, fuel batteries and flywheel batteries. The application of new energy has opened up a broad prospect for the development of electric vehicles.
2.2. Drive motor
The function of the driving motor is to convert the electric energy of the power supply into mechanical energy, and directly drive the wheels and working devices through the transmission device. At present, DC series motors are widely used in electric vehicles, with "soft" mechanical characteristics, which are very consistent with the driving characteristics of automobiles. However, with the development of motor technology and motor control technology, DC motor will be gradually replaced by DC brushless motor (BCDM), switched reluctance motor (SRM) and AC asynchronous motor because of its shortcomings such as large commutation spark, low specific power, low efficiency and heavy maintenance workload.
2.3. Motor speed control device
The motor speed regulating device is set for the speed change and commutation of electric vehicles, and its function is to control the voltage or current of the motor and complete the control of the driving torque and rotating direction of the motor.
In early electric vehicles, the speed regulation of DC motor was realized by series resistance or changing the number of turns of motor magnetic field coil. Because of its step-by-step speed regulation, additional energy consumption or complicated motor structure, it is rarely used now. At present, thyristor chopper speed regulation is widely used in electric vehicles. By changing the terminal voltage of the motor evenly and controlling the motor current, the stepless speed regulation of the motor can be realized. With the continuous development of electronic power technology, it is gradually replaced by other giant transistor chopper speed regulating devices (GTO, MOSFET, BTR and IGBT, etc.). From the development of technology, with the application of new drive motors, it will be an inevitable trend for the speed control of electric vehicles to be converted into the application of DC frequency conversion technology.
In the steering control of driving motor, DC motor relies on contactor to change the current direction of armature or magnetic field to realize motor steering, which has complicated circuit and reduced reliability. When driven by AC asynchronous motor, changing the motor direction only needs to change the phase sequence of the three-phase current of the magnetic field, which can simplify the control circuit. In addition, the adoption of AC motor and its frequency conversion speed regulation technology makes the braking energy recovery control of electric vehicles more convenient and the control circuit simpler.
2.4. Transmission equipment
The function of electric vehicle transmission device is to transfer the driving torque of the motor to the driving shaft of the vehicle. When driven by electric wheels, most parts of the transmission device can often be ignored. Because the motor can be started with load, there is no need for the clutch of the traditional diesel locomotive on the electric vehicle. Because the rotation direction of the driving motor can be changed by circuit control, the electric vehicle does not need the reverse gear in the internal combustion engine automobile transmission. When motor stepless speed regulation is adopted, electric vehicles can ignore the transmission of traditional vehicles. When electric wheels are used for driving, electric vehicles can also omit the differential of the traditional internal combustion engine transmission system.
2.5. Walking mechanism
The function of the walking device is to convert the driving torque of the motor into the force on the ground through the wheels and drive the wheels to walk. Like other cars, it consists of wheels, tires and suspension.
2.6. Steering gear
The special device is set up to realize the steering of automobile, and consists of steering machine, steering wheel, steering mechanism and steering wheel. The control force acting on the steering wheel deflects the steering wheel by a certain angle through the steering machine and steering mechanism to realize the steering of the automobile. Most electric vehicles have front wheel steering, and electric forklifts used in industry often use rear wheel steering. The steering devices of electric vehicles include mechanical steering, hydraulic steering and hydraulic power steering.
2.7. Braking device
The braking device of electric vehicles, like other vehicles, is set for slowing down or stopping, and usually consists of brakes and their operating devices. In electric vehicles, there are generally electromagnetic braking devices, which can be used to drive the motor to realize the power generation operation of the motor, so that the energy during deceleration braking can be converted into the current for charging the battery, so as to be recycled.
2.8 working device
The working device is specially set for industrial electric vehicles to complete the operation requirements, such as the lifting device, gantry and fork of electric forklift. The lifting of the fork and the tilting of the gantry are usually completed by a hydraulic system driven by a motor.
3. The technical contents of electric vehicles include:
● Power battery technology: nickel-hydrogen battery, nickel-cadmium battery, lead-acid battery, sodium-sulfur battery, lithium-ion battery, fuel battery, etc. , should have high specific power and specific energy, can meet the requirements of power and driving range: short charging time, more charging cycles, so as to facilitate use and ensure service life.
● Motor technology: There are four main types of motors: DC motor, permanent magnet motor, switched reluctance motor and AC induction motor. Light weight, high efficiency and good reliability are required.
● Control and integration technology of drive system: The control system often adopts single chip microcomputer and power device, and the power device mainly adopts IGBT.
● Battery monitoring and management system technology
● Charging system technology
● Vehicle Layout and Matching Technology of Electric Vehicles
Second, the current situation and development trend at home and abroad
Since 1990s, foreign countries have been paying attention to the research on key technologies of batteries. The three major American automobile companies have invested $2.6 billion in cooperative research, and the USABC project jointly carried out by American battery manufacturers has also targeted the batteries for electric vehicles. At present, the status quo of battery technology is far from the practical requirements of electric vehicles, which makes electric vehicles unable to compare with conventional vehicles in terms of power performance, driving range, manufacturing cost and reliability. The prospect of electric vehicles basically depends on the breakthrough of battery technology. In recent years, Ni-MH, Li, fuel and other batteries have been paid more attention, and a lot of money has been invested in research. The improvement of traditional batteries such as lead acid and Ni-Cd is also under way.
The State Science and Technology Commission and the Planning Commission organized key research projects on electric vehicles during the Eighth Five-Year Plan and the Ninth Five-Year Plan, and recently included the electric vehicle project in the Tenth Five-Year Plan. Domestic large-scale automobile enterprises, universities and scientific research institutes also take a positive attitude towards the research of electric vehicles, and have carried out several rounds of trial production by modifying electric vehicles, striving to realize the industrialization of electric vehicles at the end of the Tenth Five-Year Plan.
Three. Objectives and main research contents of the Tenth Five-Year Plan
Objective: To solve key technologies, complete the development of practical electric vehicles and realize industrialization.
② Main research contents: Overall design of electric vehicle; Advanced battery technology; Motor and control drive system; Vehicle monitoring and management system, use environment and supporting technology.
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