Electric Wheel

Brief Introduction of Electric Wheels for Mining Trucks
Mining trucks, also known as off-highway mining dump trucks, are commonly used transport vehicles for large open-pit mines. The carrying capacity is usually from 50 tons to 300 tons or even higher. At present, it is mainly divided into two forms: mechanical transmission and electric transmission. Here The discussion is about electric drive mining trucks. Its power is still provided by the diesel engine, but unlike ordinary vehicles, the diesel engine does not directly provide power to the wheels, but drives the generator, and then the generator supplies power to the wheel motor, which is driven by the wheel motor through the deceleration mechanism. Send power to the wheels. In this power transmission process, the wheel motor, the reduction mechanism and the braking mechanism are usually integrated together to form an independent unit, which is usually called an electric wheel, and some are called a wheel motor.
1 The basic structure of the electric wheel
The electric wheel has a compact structure, flexible control and high transmission efficiency, and the connection with the power source is mainly a flexible connection with cables and pipelines, so the structure design of the whole vehicle is more flexible, and it is not limited by the rigid shaft connection.
The earliest electric wheel structure appeared in the 1950s. Its structure is shown in Figure 1. It is integrated inside the wheel, located at the hub of the vehicle, and integrates an electric motor, a deceleration mechanism, and a brake. 

In the current electric wheel structure, the main part has not changed much compared with the early days, and its deceleration mechanism is usually a planetary gear mechanism. The rotor shaft of the motor transmits the torque to the sun gear in the planetary gear mechanism. Through the structure of the planetary gear, the planet carrier and the ring gear, the torque is transmitted to the rim, and at the same time, the speed is reduced and the torque is amplified to drive the vehicle.

2 Features and advantages of electric wheel mechanism
The transmission unit composed of motor and planetary gear mechanism has three notable features:
The first transmission ratio is large, so that the magnification of the torque can be large, which is beneficial to the driving of the heavy-duty vehicle. The weight of the mining truck and the self-weight of the vehicle are all in the hundreds of tons, and the output torque of the electric wheel must be large enough to realize the driving of the vehicle.
The second is smooth shifting. The speed change of the electric wheel is realized by the electric control system controlling the speed of the motor, which avoids the friction and impact of the traditional mechanical speed change mechanism, and at the same time saves the huge gear transmission structure and reduces the overall weight.
The third is compact structure. The planetary gear mechanism itself is small in size, and the motor is arranged at the corresponding position of the sun gear, so that the radial size of the entire electric wheel can be effectively controlled. Moreover, the use of electric wheels on mining trucks eliminates the need for complex transmission components such as drive shafts, clutches, differentials and other mechanical transmissions, saving a lot of space.
The above characteristics make this transmission mechanism widely used in various equipment requiring low speed and high torque. At present, many electric screwdrivers and lifting equipment, such as electric/pneumatic torque magnifying wrenches, electric/pneumatic cranes, etc., A similar mechanism is used. As shown in Figure 2 and Figure 3. 

Figure 2 Transmission structure of pneumatic crane

Figure 3 Pneumatic torque amplifying wrench

Of course, while the electric wheel mechanism has many advantages, it also has many disadvantages. For example, due to the high degree of integration, the overall weight of the wheel increases a lot, which affects the driving performance of the vehicle. And due to the limitation of the size of the hub, the radial size of the electric wheel is required to be higher, and the axial size is also required. The drive motor is required to be able to start, change speed, and stop frequently, and has high requirements for the dynamic performance of torque control.
3 Development Trend of Electric Wheels
At present, the application of electric wheels is expanding rapidly, and the trend of development from the initial application in heavy-duty vehicles to civilian electric vehicles is obvious. With the gradual improvement of energy-saving and environmental protection requirements, new hybrid models continue to appear, and power solutions such as engines, generators, and electric wheels are increasingly used in some vehicles. Many vehicle manufacturers have adopted similar electric vehicles. parts of the wheel.