2022.05.20 Hyundai Motor Group 분량9min
Hyundai Motor Group’s dedicated EV models, such as the IONIQ 5 and EV6, are boasting the ‘K-EV’ performance around the world as they have been crowned European Car of the Year and World Car of the Year. These are still getting positive reviews through auto magazines and test drive videos taken by influencers.
Its competitiveness comes from the automaker’s unique technology, such as the V2L and 800V ultra-fast charging systems housed on the E-GMP basis of Hyundai Motor Group’s EV-dedicated platform, not to mention the high-speed motor technology that demonstrates strong performance. Here are the details of the ultra-fast motor technology of the automaker’s dedicated EV.
Just as the core of internal combustion engines is the engine itself, the motor is essential to EVs. Both the engine and motor are responsible for the vehicle’s powertrain; an electric motor is a machine that converts electrical energy from the battery into mechanical energy. This is why many automakers put a lot of effort into developing a perfect electric motor.
Hyundai Motor Group increased the rotational speed of its E-GMP electric motors for enhanced performance compared to the current electric motors. Hyundai Motor Group’s IONIQ 5 and EV6 - its latest dedicated EVs - can rev up to 15k rpm; this is approximately a 33% increase compared to current motors. Genesis’ Electrified GV60 and GV70 offer more powerful performance with boost mode that instantly increases output and higher vehicle speed. These models use a high-speed electric motor (19,000 rpm) with a significantly higher top speed than their competitors. (Most EVs in the market nowadays can feature up to 15,000 to 17,000rpm)
Acceleration is amazingly improved thanks to the high-speed motor. With the boost mode activated, the GV60 performance model can feature up to 490 horsepower, doing 0-60 Mph in 4.0 seconds. Also, the Electrified GV70 can go 0-60 in 4.2 seconds despite being a derivative EV rather than an E-GMP-based dedicated EV.
The key to Hyundai Motor Group’s high-speed electric motor technology lies in the EV6 GT, which boasts the highest RPM among current EVs. The electric motors in the front and rear axles of the EV6 GT, scheduled to be released in the second half of 2022, rev up to 21,000 rpm. It provides mind-blowing performance with a speed of 260 km/h.
The electric motors built into Hyundai Motor Group’s dedicated EVs have high rotational speed. This is because the performance of an EV is closely related to the number of rotations of the motor. In order to understand this correlation, it is necessary to first understand the fact that the powertrain system of an EV is different from that of an internal combustion engine housing a multi-stage transmission with different engine and gear ratios.
The PE system (Power Electric System) responsible for driving an EV consists of a motor, a speed reducer, an inverter that changes direct current (DC) to alternating current (AC), and a battery that stores electric energy. The motor - the most essential component in driving the vehicle - generates maximum torque as soon as it starts to rotate. Based on high starting torque and stable max power, now EVs can feature higher performance than internal combustion engines.
EVs use a speed reducer rather than a transmission according to the characteristics of these motors. There are two occasions when shifting the gear in the transmission - shifting to a lower gear for higher power, and shifting to a higher gear for higher speed. EVs don’t require low gears because torque gets generated from the moment the motor rotates, nor do they need high gears since the motor can rev up to 15,000rpm. In conclusion, EVs can respond to all speeds from low to high depending on each driving situation by changing the ‘motor rotation speed’ rather than ‘gear shift.’ The motor of an EV6 GT rotates at a maximum of 21,000 rpm, so it can do 0 - 260 km/h only using the reducer, without a transmission.
Therefore, to maximize the performance of the EV, it is necessary to improve the torque, output, and maximum rotational speed of the electric motor; and it is essential to optimize the gear ratio of the reducer that affects the wheel torque and speed.
The wheel torque and wheel speed that determine the performance of these EVs can be obtained through the following formula:
- wheel torque ∝ motor torque × gear ratio
- wheel speed ∝ motor speed ÷ gear ratio
In this formula, the wheel torque - the driving force transmitted to the wheels - is the value obtained by multiplying the motor’s torque by the gear ratio of the reducer. If this value is high, the EV has excellent acceleration. The wheel speed - the rotational speed of the wheels - is obtained by dividing the speed (number of revolutions) of the electric motor by the gear ratio. The larger this value, the faster the maximum speed. Simply put, all things being equal in drivetrain systems, increasing the number of revolutions in the motor can increase the vehicle’s speed. In addition, when the torque of the motor is the same, increasing the gear ratio of the reducer improves acceleration. In fact, the electric motor of E-GMP increased the maximum rotation speed by about 70% compared to the second-generation electric motor, and improved wheel torque and speed by 20% while reducing the motor size.
EV6 GT boasts more powerful performance than other motor systems implemented in E-GMP thanks to its ultra-high-speed, high-performance electric motor. For example, the motor system of the EV6 GT has been perfected by combining a high-speed motor design, a high-output system through a dual inverter structure, and an internal cooling structure with enhanced performance to prepare for high speed. As a result, based on the high-speed motor, the performance of the motor system was significantly improved with only a single-stage reducer system.
However, improving the speed of an electric motor is not as easy as it sounds - because increasing the speed of an electric motor requires a high-level design in terms of durability, cooling, and NVH. For example, a few solutions are needed to solve the increase in centrifugal force, increase in heat loss, and increase in noise and vibration that inevitably occur as the motor becomes high-speed. Several global automakers are making EVs, but that’s why they can’t easily use high-speed electric motors as Hyundai Motor Group does.
Hyundai Motor Group solved this problem while developing the EV6 GT, creating a world-class high-speed electric motor. First, the researchers aimed to ensure the durability of ultra-fast electric motors. They improved the *stress distribution by optimizing the bearing cage, permanent magnet arrangement, and rotor core formation. In addition, the efficiency was increased by cooling the bearings inside the motor through oil lubrication. Thanks to this, the bearing was able to respond to a high speed of 21,000 rpm.
*Stress: When an external force such as compression, tension, bending, or torsion is applied to a material, it will break if the force exceeds the yield strength that is different for each size of the material.
For the inevitable heat generation of the motor due to high speed, the cooling performance of the motor was strengthened by implementing a design that minimizes power loss. The current electric motor’s water-cooling method could only cool the outside without being able to reach the coil and inside, which is the hottest part, since the coolant flows only through the housing. On the other hand, the cooling performance is greatly improved because the oil is directly sprayed from the cooling pipe in the E-GMP motor system. In particular, in addition to this basic cooling system, the EV6 GT boasts enhanced cooling performance as E-GMP can cool the core by directly spraying the cooling oil. Thanks to this structure, adequate cooling became possible even in extreme conditions when the motor rotates up to 21,000rpm.
To solve the noise and vibration problems caused by high speed, Hyundai Motor Group optimized the shape and design of the rotor shaft. The most standout feature is that forming a dual piece rotor shaft device to respond to the high-speed rotation has improved quality, compared to the current model. In addition to this, the overall design of the motor features safety, minimized amount of unbalance, and vibration and noise reduction in the high-frequency range.
Hyundai Motor Group’s dedicated EV models, including the EV6 GT, utilize new *hairpin winding technology as well as improved motor speed to increase efficiency, cooling performance, space innovation (package), and productivity. In general, hairpin windings can generate alternating current (AC) losses when rotating at high speeds; Therefore, the motor was designed to minimize the loss by analyzing the loss mechanism, which led to improved motor performance and high-speed response.
*Hairpin winding technology: The cross-section of the coil inside the motor has a rectangular structure similar to the shape of a hairpin. The coil can be wound more tightly compared to the current round wire, which reduces winding resistance and increases efficiency.
Both the high performance of the EV6 GT and the high rotational speed of the electric motor were possible thanks to the unique technology of the automaker. What is most impressive is that the EV6 GT’s high performance was also proven in actual driving - for example, the EV6 GT Influencer test drive event held in Germany in early April. The main purpose of this event was to confirm the high-speed driving performance of the EV6 GT in particular. Accordingly, many media directly confirmed the maximum speed of the EV6 GT on the German Autobahn that has unlimited speed limits.
Especially, a YouTube channel named ‘Bjørn Nyland’ showed the rotation speed, battery output, temperature, and remaining battery capacity of the electric motor getting changed in real-time according to the speed of the EV6 GT, using the dedicated tachometer (revolution-counter). In that video (Kia EV6 GT driving at 263 km/h in Germany), at a speed of 263 km/h measured by GPS, the EV6 GT’s electric motor rotated up to 20,354 rpm. Even under these extreme conditions, the battery maintained stability - the average temperature of 28 ˚C.
In addition, the EV6 GT’s electric motor and battery were impressive as they continued to maintain stability even when driving at high speed of 200 km/h or more. The moment the driver lowered the accelerator pedal, the EV6 GT’s electric motor easily exceeded 20,000rpm and boasted the highest output, and even at that moment, the battery maintained a stable temperature and power state.
As described so far, Hyundai Motor Group’s dedicated EVs are not just eco-friendly; Rather, it offers unrivaled high performance and driving experience that cannot be found in any current car. And the key to this is the ultra-fast electric motor that other automakers could not easily make. Through the high-tech electric motor with a rotation speed of 21,000 rpm, the automaker achieved two contradictory characteristics: eco-friendliness and high performance.
Hyundai Motor Group’s electric vehicle technology is continuously evolving even at this moment. The automaker is continuing research to develop a greener and more powerful electric motor, and the results will be shown by Hyundai Motor Group’s next-generation dedicated electric motor to be launched in the future.