As we all know, new energy vehicles have three core components: batteries, motors , and electronic controls. While we often see information about batteries, much less so about motors. Current new energy vehicles all use electric motor drive systems to convert electrical energy into mechanical energy to power the vehicle; therefore, the drive motor is one of the core technologies of new energy vehicles. Electric Vehicle Resources Network has selected in-wheel motors, which have gained traction in the new energy vehicle field in recent years, for this article, to help you understand what in-wheel motors are.
Introduction to Hub Motors
What is a hub motor? As the name suggests, a hub motor is a motor that integrates the wheel hub and drive unit into one unit. The motor is placed inside the wheel hub, allowing it to directly drive the wheel and propel the vehicle. Hub motor technology is also known as in-wheel motor technology. Its biggest feature is that it integrates the power unit, transmission unit, and braking unit into the wheel hub, thereby simplifying the mechanical parts of electric vehicles.
In-wheel motor technology is not new; as early as 1900, Porsche manufactured an electric car equipped with in-wheel motors on the front wheels. In the 1970s, in-wheel motor technology was applied in fields such as mining vehicles. In the passenger car in-wheel motor sector, Japanese manufacturers started research and development relatively early and currently hold a leading position. International automotive giants, including GM and Toyota, have also ventured into this technology. In recent years, domestic Chinese automakers have also gradually begun developing in-wheel motor technology.
In-wheel motor classification
A hub motor power system typically consists of an electric motor, a reduction gear, a brake, and a cooling system. Based on the type of motor rotor, the power system is divided into two types: internal rotor and external rotor.
Internal rotor type: Generally, the internal rotor type uses a high-speed internal rotor motor, equipped with a reducer with a fixed transmission ratio. To obtain a high power density, the motor speed is usually as high as 10,000 r/min. The reduction structure usually uses a planetary gear reducer with a transmission ratio of about 10:1, and the wheel speed is about 1,000 r/min.
High-speed internal rotor hub motors have the following advantages: high power-to-weight ratio, light weight, small size, high efficiency, low noise, and low cost. However, their disadvantages include the need for a speed reduction device, which reduces efficiency, increases unsprung mass, and limits the maximum speed of the motor to factors such as coil losses, friction losses, and the capacity of the speed-changing mechanism.
Because in-wheel hub motors require integrated reducers, the front wheels of passenger vehicles must accommodate the motor, reducer, brakes, steering system, and other components within their limited space. Therefore, in-wheel hub motors are rarely used in passenger vehicles. Theoretically, in-wheel hub motors with internal rotor reducers offer higher power density and a more compact structure, but due to their complex manufacturing process, current products are not yet in mass production.
External rotor type: The external rotor type usually uses a low-speed external rotor motor. The maximum speed of the motor is about 1000-1500 r/min. There is no reduction gear. The external rotor of the motor is fixed to or integrated with the rim of the wheel. The speed of the wheel is the same as that of the motor.
The advantages of low-speed external rotor motors are simple structure, small axial dimension, high power specificity, torque control over a wide speed range, fast response speed, and high efficiency because the external rotor is directly connected to the wheel and there is no reduction gear. The disadvantages are that to obtain a larger torque, the size and weight of the engine must be increased, resulting in high cost, low efficiency during acceleration, and high noise.
External rotor hub motors eliminate the need for half-shafts and reducers, but they are significantly larger. Without a reducer, achieving the required torque necessitates lowering the rotational speed. As is well known, with constant torque, power is directly proportional to speed; insufficient speed limits power density, resulting in a large size and high weight. Despite their size and weight, external rotor hub motors are relatively simpler in structure, have fewer drive chains, and are more efficient than internal rotor hub motors, and some companies have already entered mass production.
Advantages and disadvantages of hub motors
advantage:
1. High efficiency, increasing driving range.
Hub motors are highly efficient because they simplify the mechanical transmission structure, including the reducer, gearbox, and forklift, significantly reducing chassis weight and overall vehicle weight. Simultaneously, they eliminate transmission losses, improving system efficiency and potentially increasing driving range by approximately 10%.
2. The chassis is simplified, eliminating the need for mechanical connections.
By using in-wheel motor technology, the chassis structure is optimized, eliminating the need for mechanical components such as axles and driveshafts. Furthermore, long-standing chassis issues such as NVH (noise, vibration, and harshness) and dynamics are significantly simplified. Reduced system complexity allows for a corresponding reduction in chassis development time, from three years to one year, or even less.
3. The four wheels can drive independently, enabling a variety of complex driving modes.
With all four wheels capable of independent drive, the power distribution to each wheel can be dynamically adjusted, significantly improving vehicle stability and dynamism on various road surfaces. Furthermore, four-wheel drive enables on-the-spot steering and lateral movement, helping to address the parking challenges that novice drivers often face.
4. Facilitates the adoption of various new energy vehicle technologies.
Since pure electric vehicles, plug-in hybrid electric vehicles, and fuel cell vehicles all require electric drive, in-wheel motors can be used in any type of new energy vehicle. Furthermore, regenerative braking technology for new energy vehicles can also be applied to in-wheel motor-driven models.
shortcoming:
1. Increased unsprung mass affects vehicle handling.
Increased unsprung mass significantly increases the dynamic load on the tires and the root mean square value of the vehicle's vibration acceleration. This leads to increased vertical vibration amplitude, affecting tire contact characteristics and negatively impacting vehicle dynamics and ride comfort.
2. The motor is prone to overheating.
Because cars often operate under heavy loads, such as climbing hills, and the in-wheel motor is located within the very limited space of the wheel, it is prone to overheating. Overheating of the motor will affect the torque density and may also cause demagnetization of the magnets.
3. Relatively high cost
Because the industrialization of hub motors is still incomplete and the technology is monopolized by a few companies, their cost is relatively higher than that of centralized motors, which are already highly industrialized.
