Nowadays, the drive motor layout space in the new energy vehicle design is limited, under the condition of meeting the space layout of the vehicle, but also comprehensive motor control system on the motor rotation response time requirements, which requires a reasonable choice of electric length diameter ratio, coupled with the current lightweight, integration trend, the rational and efficient miniaturization of the motor has become very important. The size of the motor is a certain size requirements, similar to people’s “height”, the axial length of the motor L is similar to people’s “height”, the motor diameter D is similar to people’s “circumference”, the ratio of the two is the length-diameter ratio, to determine the motor’s length-diameter ratio, we must first determine a series of key parameters of the motor. As we all know, the power of the motor = speed * torque. The volume and power of the motor is not too direct relationship, the motor wants to miniaturize, you need to consider increasing the output power in the case of constant volume (output power = magnetic load × electrical load× speed), which means that the volume can be smaller in the case of constant output power.
How to improve the overall output power and reduce the loss under the premise of the same volume is the main difficulty of the motor becoming smaller. The main two factors affecting the output power of the motor, one is the speed, one is the torque, the product of the two is high, the output power is large, in addition to the need to consider the electrical load of the motor A (the effective magnetic flux of the motor magnetic circuit) and magnetic load B (the number of ampere-turns when the coil is energized).
Only the motor has a large current or high magnetic density can use a smaller motor to produce a larger torque, and the motor to pass a large current, it will produce resistance loss and heat, which will lead to a disproportionate cost and benefit, so it can only improve the magnetic density, that is, the magnetic induction intensity. The energy of permanent magnet motor is transmitted through the air gap between fixed and rotor in the form of electromagnetic energy, so the motor design must deal with various magnetic densities, such as air gap magnetic density, tooth magnetic density, yoke magnetic density, average magnetic density, and maximum magnetic density.
To increase magnetic load B, it is necessary to have good magnetic conductive materials. Due to the saturation effect, the maximum magnetic density in the electrical steel sheet can only reach about 2T, due to the existence of tooth slots, so the air gap magnetic density is less than 2T, generally around 1T, in order to achieve a higher magnetic density, the need for high current electromagnetic coil to excite or excitation with high remanence permanent magnet.
High current electromagnetic coil itself will heat, there is a current limit, high remanence permanent magnets are rare metals, very expensive, so the magnetic load also has a limit.
In addition, there is a way to reduce the volume of the motor, that is, in the case of constant power, if you want to reduce the volume of the motor, you can reduce the motor torque, which will increase the motor speed, and finally use the reducer to achieve the purpose of volume reduction.
Post time: May-22-2024
