Core Components Of New Energy Vehicles: Global Trend Of Drive Motors (2)

- Jul 18, 2018-

Technological evolution

Judging from the classification of motors, there are mainly four types: DC, AC induction, permanent magnet synchronous and switched reluctance. the latter three types are mainly used in new energy automobile motors.

At present, permanent magnet synchronous is the mainstream motor type due to its superior performance. Ac asynchronous motors are moderately priced but have somewhat poor performance and are used by some manufacturers in the United States and China. The main advantage of switched reluctance motor is its low price, but there are also technical problems of noise and vibration. if these problems can be solved, switched reluctance motor will have a large market.

Ac asynchronous motor: although AC asynchronous motor does not have advantages over permanent magnet synchronous motor at present, its cost is much lower than that of permanent magnet synchronous motor. In terms of volume, AC asynchronous motor is larger than permanent magnet synchronous motor, which is mainly limited by the design structure. 

Permanent magnet synchronous motor: the motor is internally provided with a rotor wrapped with permanent magnets, so the overall system power is high and the volume is small at the same time. The cost is relatively expensive, mainly due to the high price of permanent magnet materials. At present, research on reducing the use of permanent magnets is underway. at the same time, research also focuses on improving the output efficiency of magnets. Permanent magnet motor is currently the most widely used motor type in electric vehicle motor industry.

Switched reluctance motor: the price of switched reluctance motor is very competitive, mainly because there is no high cost permanent magnet in its rotor and its power is moderate. Because the pulling force of stator and rotor is used to provide power, vibration and noise caused in the process are its main problems. As the electric vehicle motor is currently in a period of rapid increase, we believe that the increase in demand will speed up technological innovation and replacement.

Direction of motor technology promotion

By studying the trend of motor technology evolution in the past 20 years, we find that there is still much room for further improvement in motor technology. First look at the thickness of the steel used for the movement. For the stator and rotor, it is mainly composed of thin electromagnetic steel layer superposition. in 1997, the first generation Toyota Prius used 0.35 mm steel layer, which was then reduced to 0.3 mm, and recently dropped to 0.25 mm in 2016. Generally speaking, the increase in the number of thin steel layers can increase the efficiency of the motor and also help to control the temperature of the motor. 

At present, manufacturing thin steel is a major technical problem in the industry. The main difficulty lies in controlling springback in die casting and keeping the consistency of steel sheet materials. Judging from the current situation, rotary forging technology will increasingly become the mainstream manufacturing method of the industry due to its advantages in cost and production efficiency.

Secondly, in terms of winding density, the amount of winding in the stator as a whole is an important factor that determines the power level of the motor. However, the amount of winding is mainly determined by the number of turns the copper wire can make around the movement in a limited space. In terms of technology, the current use of the inserter is suitable for high-power stator processing, and has gradually become the standard of production in the industry.

In terms of coil types, there are mainly two types: square and circular. at present, the mainstream manufacturers use circular. however, due to its high space utilization rate, square technology is gradually replacing circular as the general direction of the industry, while Toyota and Honda have begun to use square winding technology in batches. On the side of other manufacturers, An Chuan motors has begun to develop electronic winding technology with the aim of improving control and efficiency.

Finally, in terms of cooling system, it is divided into two parts: motor and inverter. as the magnetic force of permanent magnet motor will decrease with the increase of motor temperature, the efficiency of cooling system is very important for high power operation of motor. 

Judging from the trend of technological evolution, the mainstream cooling technology has developed from air cooling and water cooling to the current stage of oil cooling. Its main technical method is to immerse the motor into the oil cooling chamber to cool down. Although some experts believe that friction with oil will reduce the efficiency of the motor, oil cooling is still the most effective cooling mode under the current technical conditions. Regarding inverters, the cooling system is also important to the performance of inverters.

Nissan recently claimed that in the new leaf 2017 model, the output power of the motor was increased from 80 kw to 110 kw by lifting the inverter cooling system, while other parts of the motor were the same as those of the previous generation. 

This shows the importance of inverter cooling system. Although the use of silicon carbide will improve the heat resistance and pressure resistance of the motor, its relatively high cost and the time point for its large-scale application may be difficult to come in the short term.

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