Research And Thermal Analysis Of Drive System For Electric Balanced Vehicle

In recent years,with the increase in the number of cars,the environmental problems brought by automobiles have become more prominent.It is urgent to gradually replace the status of cars in daily travel with more environmentally-friendly vehicles.At this time,the electric balanced vehicle appears in people’s field of vision with its environmentally-friendly and convenient characteristics.The drive system is the main component of the balance vehicle.In order to ensure the torque performance of the balanced vehicle,the low-speed permanent magnet brushless DC motor is the widely used in the balanced vehicle.The disadvantages are low efficiency and low power density.Therefore,a medium-speed permanent magnet brushless DC motor is selected to replace the low-speed one.At the same time,in order to improve the stability and noise caused by the medium-speed motor,the cycloidal pinwheel reducer is placed inside the permanent magnet brushless DC motor.This assembly method does not increase the axial dimension of the system.Firstly,the research background and significance of the subject,the development history of the relevant research,along with the structural arrangement of the paper are expounded.The overall assembly form of the drive system and the structural of two main components are designed.Based on the dynamic performance requirements of the balanced vehicle,the size of the cycloidal pin wheel mechanism is calculated,a three-dimensional model of the cycloidal wheel is established,and perform dynamic simulation is carried out.Then,the electromagnetic designing is done according to the permanent magnet brushless DC motor in the power requirements and the size of the cycloidal pin mechanism.The static field and transient field of the motor are analyzed in the electromagnetic simulation software to ensure the reasonable design of the brushless DC motor.The loss of the motor will inevitably occur during the operation,the loss is the basis of temperature analysis.Therefore,the theoretical analysis and numerical calculation of the iron loss and copper loss in the motor are carried out respectively.The eddy current loss and mechanical loss of the motor are calculated.The variation law of four kinds of losses with motor speed are studied.Secondly,the equivalent thermal conductivity and surface heat dissipation coefficient of each part of the motor required for heat transfer are calculated according to the boundary conditions of temperature calculation,and the motor temperature field is simulated in the finite element software.Using the loss value calculated by the motor,the electromagnetic field and the temperature field are directly coupled and calculated.In the coupled field,the boundary condition is added to the motor to obtain the unidirectional coupled temperature field of the motor.Since the temperature change has a great influence on the properties of the material,the unidirectional coupling is done,the difference between two coupled ways is analyzed.At the same time,the temperature variation of the two coupled fields during the change of motor speed is studied.Finally,refering to the basics of circuit science,the concept of thermal path is introduced in heat transfer,and the equivalent thermal path model is established according to the heat path diagram and the thermal path law,and the thermal path simulation model is built in the simulation software.The parts in the motor are equivalent to hollow cylinders,the equivalent thermal resistance of each part is calculated,and then the thermal conductivity value is calculated,the loss value,thermal conductivity value and heat capacity value of each part of the motor are input into the model.Getting the temperature rise curve of the motor without the closed loop feedback link.Comparing the unidirectional field with the non-closed loop result,it’s found that the error value fluctuates within a reasonable range.Considering the influence of temperature on the stator winding of the motor,the feedback function is added to the thermal path model,that is,the closed-loop feedback link is added to study the difference between the result of adding the closed loop and the result without the closed loop.The bidirectional field is compared with the closed-loop result,the comparison errors of the two results are within a reasonable range.The temperature simulation results of the finite element method and the equivalent thermal path method show that the temperature rise of the motor designed in this paper is within the acceptable range,which proves the feasibility of the design of the brushless DC motor.