Global automotive technology is evolving towards energy conservation, environmental protection, and safety. Since a car's energy consumption is directly proportional to its weight, reducing unnecessary energy consumption requires minimizing the car's weight while ensuring safety. For electric vehicles, the battery, motor, and body structure constitute a significant proportion of the total vehicle weight. Reducing the weight of these components significantly contributes to the overall lightweighting of electric vehicles.
This article introduces structural contact nonlinear analysis of drive motor rotors, providing data support for the next step of rotor structure shape optimization while ensuring that the structural strength meets the design requirements.
Simulation Analysis Description
The embedded permanent magnet motor employs a rotor lamination design with embedded magnets and symmetrically distributed magnetic poles. This not only optimizes the back electromotive force waveform but also effectively suppresses cogging torque and load torque disturbances. During high-speed operation, the motor rotor structure primarily bears the effects of centrifugal force, electromagnetic force, and the attractive force of the permanent magnets. Research results indicate that centrifugal force is the main factor affecting the structural strength of the motor rotor. This paper focuses on the structural strength of the motor rotor under centrifugal force during the rotor structural strength analysis. The geometric model of the motor rotor is shown in Figure 1.
Model preprocessing
In SCDM, a rotor lamination and magnet model was created. The rotor outer diameter is 100mm, and there are 12 magnets. Contact pairs (12 pairs) were established between the rotor laminations and magnets, defined as frictional contact with a friction coefficient of 0.15. The mesh was then created, resulting in 320,000 nodes and 64,000 elements.
Solution setup and boundary conditions
In the solution settings, enable the automatic time step function, set the load step to 1s, the initial substep to 50, the minimum substep to 10, and the maximum substep to 100.
A fixed constraint is applied to the inner ring of the rotor, and a frictionless constraint is applied to both sides of the rotor and the magnet. The entire model is subjected to an angular velocity of 1200 rad/s.
Calculation process and results
5.1 Calculation Process
Because of the contact nonlinearity in the calculation, the calculation process needs to be solved iteratively. The calculation process curve is shown in the figure below.
5.2 Analysis of Calculation Results
The maximum stress on the rotor is 64 MPa, which occurs in a narrower part of the lamination. The maximum displacement is 0.0028 mm, which occurs on the outermost side of the rotor contact position.
The main contact points between the rotor laminations and the magnets are the outer sides of the laminations and the bosses. This is because the magnets are subject to centrifugal force and tend to move outwards.
Centrifugal force causes the magnet to move outward until it is tightly connected to the lamination. Except for localized areas, the overall displacement follows the rule that the further away from the axis, the greater the displacement, with a maximum of 0.0028 mm. At the corner where the magnet and lamination intersect, relatively large local stresses appear, with a maximum stress of 64 MPa. This connection area is narrow and has weak rigidity. Furthermore, stress concentration is clearly present at the bosses where the rotor lamination openings are located.
in conclusion
As can be seen from the above figure, the conclusion that can be drawn from the above nonlinear analysis is:
1) At a rotational speed of 1200 rad/s, the rotor deformation and stress caused by centrifugal force will not cause structural damage;
2) The connection between adjacent magnets is a vulnerable part of the structure, and it is advisable to increase the width of this part appropriately.
Rotor strength analysis is the foundation for optimization design. Only when sufficient strength is guaranteed can there be room for further structural optimization.
The structural strength analysis method for motor rotors developed in this paper can effectively guide the design of motor rotors and be applied to subsequent motor product development processes.
By implementing simultaneous simulation and design engineering, CAE work can be involved in the conceptual design stage, allowing design defects to be discovered as early as possible and structural improvements to be made in a timely manner. This can minimize design problems, improve design reliability and quality, and shorten the design cycle.
