The wheel hub motor drive technology is also known as wheel-mounted motor technology. Its biggest feature is the integration of power, transmission and braking devices into the wheel hub, thus greatly simplifying the mechanical parts of electric vehicles.
The wheel hub motor drive system is mainly divided into two structural types according to the rotor type of the motor: inner rotor type and outer rotor type. The outer rotor type uses a low-speed outer rotor motor, the maximum speed of the motor is 1000-1500r/min, and there is no deceleration device, and the wheel speed is the same as the motor; while the inner rotor type uses a high-speed inner rotor motor with a fixed transmission ratio reducer. In order to obtain higher power density, the speed of the motor can be as high as 10000r/min.
1) Bearing and driving. Bearing and driving is a necessary function of the wheel hub motor. The load bearing is realized by relying on the axle bearing to realize the centering of the rotor and the stator. The wheel rim of the vehicle is connected to the suspension axle housing through the axle bearing instead of the stator and rotor to carry the road shock absorber and load. The driving method is that the outer rotor is directly connected to the rim to achieve the purpose of direct driving.
2) Electronic differential speed control. Electronic differential control is also one of the functions of the wheel hub motor. The realization method is front-wheel steering, which is completed by an ordinary steering gear; the rear wheel needs slip, which is completed by an electronic differential; the turning radius is determined by the front-wheel steering angle, and the rear wheel slip is determined by the vehicle turning radius and wheelbase. The slip of the rear wheels is calculated from the rotation angle of the front wheel steering gear. The steering machine can also be an electronic steering. Even if the rear wheel cannot strictly differentiate, the inner wheel should change from "active" to "slave", which is achieved by disconnecting the motor or connecting a compensation resistor in series in the loop.
3) Braking energy recovery. The function of the wheel hub motor is also the recovery of braking energy. During the braking process of an electric vehicle, the kinetic energy of the vehicle is transferred to the motor through the wheels, thereby driving the motor to rotate. At this time, the motor is working in the power generation state, charging the energy storage device, that is, the battery or super capacitor, and converting the braking energy into electric energy and storing it in the energy storage device to realize energy regeneration. At the same time, the resistance torque generated by the motor acts on the wheels to generate a braking torque, which plays a role in deceleration and braking.
4) Cooling of the motor. There are two cooling methods for wheel hub motors, air cooling and water cooling. Air cooling uses a structure conducive to gas circulation to cool the wheel hub motor, such as a built-in cooling fan; water-cooling, a special cooling fluid channel is set up, and the wheel hub motor is cooled by heat exchange with the liquid.
5) Braking system integration. The function of the wheel hub motor also includes brake system integration. The braking system includes electric braking and friction braking, and the integration of friction braking is generally a disc brake. The rotating element in the friction pair of the disc brake is a metal disc that works on the end face, which is called a brake disc. The friction element clamps the brake disc from both sides to generate braking.