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Overview of technical characteristics and energy saving principles of electric vehicle range extenders

Overview of technical characteristics and energy saving principles of electric vehicle range extenders

[Abstract]:
The mainstream extended-range electric vehicles use the first type. Because of the very high manufacturing cost of hydrogen fuel cell stack extenders, the cost of vehicle use is also very high, and the potential safety risks of the vehicles are too large, so such extended range systems are basically being eliminated. edge. So let's focus on the internal combustion engine range extension system, which is an "ancient technology".
The role of the range extender is as the name implies: it increases the vehicle's range and is suitable for electric vehicles. There are two types of range extenders, as follows.
 
1. Extender for internal combustion engine and generator combination
 
2. Hydrogen fuel cell stack chemical power range extender
 
The mainstream extended-range electric vehicles use the first type. Because of the very high manufacturing cost of hydrogen fuel cell stack extenders, the cost of vehicle use is also very high, and the potential safety risks of the vehicles are too large, so such extended range systems are basically being eliminated. edge. So let's focus on the internal combustion engine range extension system, which is an "ancient technology".
 
First, reasons for the popularity of extended range technology-high stability.
 
Vehicles using range extenders can refer to diesel locomotives or ships. These vehicles are characterized by large volume and high quality. Direct combustion with internal combustion engine and gearbox will have very high fuel consumption and poor stability; for example, early The train tried to drive the vehicle with a diesel engine and a gearbox. During the test, the transmission shaft of the gearbox was interrupted due to the high torque of the engine. Therefore, this type of vehicle cannot be driven by a fuel oil vehicle. The only alternative method is to use a direct-drive motor and a diesel engine to generate electricity.
 
 
The structure of the internal combustion engine used by ordinary cars is very complicated, and the combination of cylinder, piston, connecting rod, crankshaft and other structures can realize the conversion of thermal energy into torque. The structure of the motor is very simple. Only one "crankshaft" can be converted into torque by the electromagnetic field. The simple structure can not only reduce the failure rate and increase reliability, but also can achieve high speed due to almost no vibration and controllable wear. Running; that is, the motor can skip the gearbox and drive the vehicle directly, which solves the problem that heavy vehicles cannot be driven by internal combustion engines.
 
 
The use of electric motors requires power consumption. After all, the battery pack capacity of vehicle equipment is limited. To achieve long-distance battery life, it is necessary to generate electricity while driving. Therefore, the eliminated internal combustion engine is used in combination with a generator motor to use fuel oil to generate electricity. Charge the battery pack, and then use the motor drive to make the vehicle have unlimited battery life as long as it can save fuel. This is the early range-extended diesel locomotive. Some special ships and even nuclear submarines are also this system; including today's high-speed rail cars, this structure is the same. The difference is that the internal combustion engine is not used to generate electricity, but the power is immediately obtained through the grid.
 
 
Second, the reasons for the application of extended range technology for small and mini buses-high conversion efficiency.
 
If it is said that heavy-duty vehicles need to skip the gearbox and use direct-drive electric motors to drive the internal combustion engine to increase the range; theoretically, a small family scooter (small micro passenger) is not necessary, because even using a gearbox can Guaranteed stable, reliable and durable. However, if you consider energy saving, it is more reasonable to increase the program because of the conversion efficiency.
 
1. The thermal efficiency of internal combustion engines is generally 30% ~ 40%
 
2. The energy conversion efficiency of electric motors generally exceeds 90%
 
In short, if you consume 44,000 kilojoules of thermal energy from a kilogram of gasoline, only 30% or 40% of this thermal energy is converted into kinetic energy, and most of the other is lost by the cooling system and sports wear, which is waste. There is a large loss in driving a car with this engine, and 90% of the electricity consumed by an electric car can be converted into effective work. Using a motor to drive can reduce waste.
 
 
Then the use of motor drive can achieve constant torque and large torque with efficient power conversion, and is completed in the low speed range. As long as the engine torque is large enough, high horsepower can be achieved at low speeds. The horsepower calculation formula is [(N · m × rpm ÷ 9549) × 1.36]. The torque N · m and the speed RPM are the basis for increasing horsepower. However, the higher the speed, the higher the fuel consumption and power consumption of the engine, so the most ideal state is to achieve the high horsepower required by low speed and high torque.
 
However, this state of the motor can do that of the internal combustion engine, because the motor conversion rate is high and the current output speed is extremely fast and controllable. The internal combustion engine must increase the intake air volume by increasing the speed and increase the torque in a multi-fuel injection state. At the same speed (horsepower demand), the electricity consumed by the motor drive of the vehicle is converted into fuel oil. The energy consumption will always be much more than that of the engine.
 
Therefore, the vehicle also needs to be driven by an electric motor, and the internal combustion engine only needs to run at low power to be responsible for generating electricity. The electric power consumption of electric vehicles is getting lower and lower, and its power consumption per 100 kilometers is assumed to be 20kwh. However, for an internal combustion engine to drive a direct-drive automobile, the required horsepower will inevitably be too high. The difference in horsepower is equal to the difference in speed (fuel consumption). This is why the internal combustion engine uses fuel to generate electricity.
Summary: Extended range electric vehicles can achieve much lower fuel consumption than similar-grade fuel vehicles, so most first-line PHEV vehicles have a REEV extended range driving mode. Most of the mass-produced electric vehicles are not equipped with a range extender before leaving the factory, and most require the owner to install the range extender after purchase; most of the vehicles providing optional range extenders are heavy-duty vans, some of which are luxury buses. Provide a range extender for use as an A-type RV. Ordinary family scooters can only drive long distances by planning the time and ensuring that the range extender fuel tank is full.