Brake integration technology
The hub motor is installed in the hub of the drive wheel, occupying the space where the mechanical brake caliper and the brake disc are originally arranged, and the original mechanical brake cannot be used. If the electric motor is only braked by the electric motor of the hub motor, there is a problem that the braking force is insufficient, the electric regenerative braking cannot be realized when the remaining battery power is insufficient, and the braking reliability is low. At present, the hub motor has an integrated solution of mechanical braking, but the scheme is not mature. The annular brake disc has a large braking force, the friction plate has a small braking area, and is easy to deform, shake, and generate a large amount of heat. Such problems, its braking ability and reliability have yet to be verified.
Hub motor cooling technology
Because the wheels often need to be under heavy load and low speed climbing and long slope conditions, and the motor is placed in a small wheel, it is easy to cause the problem that the motor is overheated and burned due to insufficient cooling. However, the hub motor is directly affected by the vibration of the ground, and the muddy sand of the road surface is reduced. The environment is very bad. From the perspective of the protection and maintenance of the hub motor, the tighter the motor, the better, which makes the hub motor The heat generated during operation is more difficult to dissipate outside the motor, making it difficult to cool the motor. Therefore, the heat dissipation and forced cooling of the motor need to be solved.
There are two main solutions for hub motor cooling:
1 In the structural design of the electric wheel, it is considered to use a gas (wind) to cool the motor, and an electric wheel structure that facilitates the circulation of the gas is applied to cool the hub motor. For example, Ryunosuke Kawashima and others have designed a cooling fan that specifically cools the brake disc and the hub motor. The solution installs a blade-shaped spoke in the hub, and uses the rotation of the blade-like spoke to generate airflow to cool and dissipate the brake disc and the hub motor. The designed cooling fan was installed on a real vehicle for testing. The results show that a car equipped with a cooling fan needs to consume 2% to 4% more energy, but it can enhance the flow of air and increase the swirl of gas at the wheel population. Flow, so that the motor achieves better heat dissipation.
2 In the structural design of the electric wheel, liquid (water) is considered to cool the motor, and a special coolant (water) channel is provided to cool the hub motor by heat exchange with the liquid. For example, RoyjiMimtani is equivalent to applying for a US invention patent entitled "High Efficiency Cooling Hub Motor" in 2010. In the invention patent, an oil pump is arranged at the end of the rotating shaft of the hub motor, and the oil in the oil tank is put into a specially arranged cooling passage until reaching the stator of the motor through the action of the oil pump, and the stator is cooled by heat exchange between the oil and the stator.
In summary, the hub motor still has many problems such as high speed instability, unequal spring quality, high heat dissipation in a high sealing environment, brake integration problem, energy management to be optimized, etc., but many technical problems, if lack of scale For business applications, the breakthrough speed will be slow. This paper believes that the miniaturized low-speed electric vehicles are less sensitive to the above problems, and the application breakthrough of batch production should start from this field, and at the same time, it can accumulate technology and use resources for the application of hub motors in high-speed vehicles.
