How to judge the quality of the motor

In the era of electric vehicles, how should we evaluate the quality of electric motors?

Perhaps many people think that the type of motor determines the quality of the motor.

As the two most commonly used motors at present - permanent magnet synchronous motors and AC asynchronous motors, although the outside world has different opinions on the two types of motors, in fact, both have their own advantages, and they cannot be simply evaluated based on type.

Some people also believe that the quality of a motor should be related to its performance parameters, such as acceleration, top speed and power consumption. No matter what type of motor it is, as long as these three parameters are higher, the motor is better.

But in fact, top speed, acceleration and power consumption cannot determine the quality of a motor, because behind them, there is another core factor that limits their upper limit, resulting in the motor being unable to achieve more extreme performance.

The core of truly evaluating the quality of a motor is heat dissipation. Whether it is the acceleration capability of a tram, the sustained top speed performance, or the economical power consumption level, it is inseparable from the support of heat dissipation. Heat dissipation determines both the upper limit and the lower limit of the motor.

For example, permanent magnet synchronous motors are particularly dependent on heat dissipation because their rotors use permanent magnet materials. Under high temperature conditions, the permanent magnets are at risk of complete demagnetization, which is irreversible.

However, since the AC asynchronous motor uses a traditional coil winding structure for its rotor, it will emit a large amount of heat when running at full load. The excessively high temperature will not only melt the various insulating materials inside, but in extreme cases it can even melt the windings.

Therefore, in order to ensure that it does not overheat, many car companies strictly limit the motor speed, which results in many electric vehicles being unable to achieve extreme acceleration, top speed and other performance; only when the heat dissipation is improved can the motor be freed from limitations and have the possibility of continuing to develop upward.

What should excellent motor cooling look like?

Many car companies are now working on improving the technology layout for motor heat dissipation capabilities, focusing their upgrade efforts on flat wire motors, thin-film lamination technology, and oil cooling systems.

Flat wire replaces round wire

Compared with traditional round wire motors, flat wire motors can not only improve working efficiency by about 10%, but also improve heat dissipation capacity by 10%, which can be said to be an all-round improvement.

In a round wire motor, the stator winding is composed of many round copper wires, which have limited ability to share current and low space utilization, which in turn releases more heat.

The flat wire winding uses rectangular copper bars to completely fill the slot space in a simple stacking manner. The current can be distributed by the flat wire with a thicker diameter and larger surface area, thereby reducing heat generation.

In this regard, the permanent magnet synchronous motors equipped in Tesla's Model 3 and Model Y use 10 layers of flat wire windings. Although the more flat wire windings are not necessarily better, while improving heat dissipation, it is hard to say that Tesla's advantages of low power consumption and high top speed are not due to these 10 layers of flat wire windings.

Using a thin film lamination process

The motor rotor structure using the thin-film stacking process looks like countless cucumber slices put together as a whole. Car companies choose to cut the rotor into countless thin slices to reduce the size of the rotor and the generation of current loops. The slices are connected by welding and other processes.

But the biggest beneficiary of the thin-film lamination process is the permanent magnet embedded in it, because it is most sensitive to high temperature. As long as the temperature of the rotor is controlled, the pressure on the permanent magnet can be much smaller.

In this regard, you can refer to BYD's motor. In addition to using the thin-film lamination process, BYD even added a small amount of silicon to the manufacturing material of the rotor sheets to change the conductivity of the rotor and thus control heat.

Use oil cooling instead of water cooling

Oil cooling can reach places that water cooling cannot reach, and since it is non-conductive and non-magnetic, it can directly reach into many areas inside the motor that water cooling pipes cannot reach, thus greatly improving the heat dissipation capacity.

In this regard, the average peak temperature of the oil-cooled motor of the Wenjie M5 can be reduced by 30°C, allowing the motor to obtain a stronger performance ceiling and sustained capability, such as repeated acceleration from 0 to 100 km/h 15 times without attenuation, and more stable high-speed driving for a long time.

Summarize

Many domestic and foreign automakers and motor suppliers are actively promoting the corresponding technologies and processes around heat dissipation performance. In fact, there is still a lot of room for optimization. Some have achieved good results, but they cannot be mass-produced because the cost cannot be reduced in a short period of time. As the cost of related technical materials and processes gradually decreases, the heat dissipation performance of the motor will eventually improve steadily. After completely removing the seal of "heat dissipation", the overall performance of the motor will also truly undergo a qualitative change.