In the era of electric vehicles, how should we evaluate the quality of motors?
Many people might think that the type of motor determines its quality.
As the two most commonly used types of motors—permanent magnet synchronous motors and AC asynchronous motors—although there are different opinions about the two types of motors, they each have their own advantages, and one cannot simply judge their quality based on their type.
Some people believe that the quality of a motor should be related to its performance parameters, such as acceleration, top speed, and power consumption. Regardless of the type of motor, the higher these three parameters are, the better the motor is.
However, in reality, top speed, acceleration, and power consumption cannot determine the quality of a motor, because there is another core factor that limits their upper limit, preventing the motor from achieving more extreme performance.
The core factor in truly evaluating the quality of an electric motor is heat dissipation. Whether it's an electric vehicle's acceleration, sustained top speed, or economical energy consumption, all rely on proper heat dissipation. Heat dissipation determines both the upper and lower limits of a motor's performance.
For example, permanent magnet synchronous motors are particularly reliant on heat dissipation because their rotors use permanent magnet materials. Under high temperatures, permanent magnets are at risk of complete demagnetization, and this process is irreversible.
AC asynchronous motors, due to the use of traditional coil winding structures in their rotors, will generate a lot of heat when running at full load. Excessive temperature can not only melt various internal insulation materials, but in extreme cases, it can even melt the windings themselves.
Therefore, in order to prevent overheating, many car manufacturers strictly limit the motor speed, which prevents many electric vehicles from achieving their full acceleration and top speed performance; only by improving heat dissipation can the motor be freed from these limitations and continue to develop.
What constitutes excellent motor cooling?
Many automakers are now focusing their technological efforts on improving motor cooling capabilities, concentrating their upgrades on flat wire motors, thin-film stacking processes, and oil cooling systems.
Flat wire replaces round wire
Compared to traditional round wire motors, flat wire motors can improve work efficiency by about 10% and heat dissipation by 10%, which can be described as an all-round improvement.
In a round wire motor, the stator winding is composed of many round copper wires, which has limited ability to distribute current and low space utilization, thus generating more heat.
Flat wire windings completely fill the slot space by using rectangular copper bars in a simple stacking manner. The current can be distributed by the flat wires, which have a thicker diameter and larger surface area, thereby reducing heat generation.
In this regard, the permanent magnet synchronous motors in Tesla's Model 3 and Model Y use 10 layers of flat wire windings. Although more flat wire windings are not necessarily better, it is hard to say that the advantages of Tesla's low power consumption and high speed are not due to these 10 layers of flat wire windings.
Using thin-film stacking process
The motor rotor structure, which uses a thin-layer lamination process, looks like countless cucumber slices pieced together into a single unit. Automakers choose to cut the rotor into numerous thin slices, reducing both the rotor's size and the number of current loops. The slices are then connected using processes such as welding.
However, the biggest beneficiary of the thin-film stacking process is the permanent magnet embedded within it, as it is most sensitive to high temperatures. As long as the rotor temperature is controlled, the pressure on the permanent magnet can be reduced significantly.
In this regard, we can refer to BYD's motors. In addition to using a thin-film stacking process, BYD has even added a small amount of silicon to the material used to make the rotor thin films, thereby changing the conductivity of the rotor and controlling the heat.
Replace water cooling with oil cooling
Oil cooling can reach places that water cooling cannot, and because it is neither conductive nor magnetic, it can directly penetrate into many areas inside the motor that water cooling pipes cannot reach, thus significantly improving heat dissipation.
In this regard, the oil-cooled motor of the Wenjie M5 can reduce the average peak temperature by 30°C, which allows the motor to achieve a stronger performance limit and continuous capability, such as no degradation after 15 repeated accelerations from 0 to 100 km/h, and more stable long-term high-speed driving.
Summarize
Many domestic and international automakers and motor suppliers are actively advancing technologies and processes related to heat dissipation performance. There is still significant room for improvement, and some have already achieved considerable success, but mass production is hindered by the inability to reduce costs in the short term. However, as the costs of related technologies, materials, and processes gradually decrease, the heat dissipation performance of motors will eventually improve steadily. Once the bottleneck of heat dissipation is completely removed, the overall performance of the motor will truly undergo a qualitative leap.
