# Simplified Design of Magnetic Gear by Considering the Maximum Transmission Torque Line
## 3 Maximum Transmission Torque Line and Design Parameters of Magnetic Gear  
### Maximum Transmission Torque Line  
From the various designs of magnetic gears which followed the fixed conditions stated in Section 2.1, the analysis of the magnetic gears is conducted by using Finite Element Analysis Method (FEM) to study effect of volume of PM on the transmission torque. The total volume of PMs is varied by changing the parameters of MG, including the thickness of PMs. As shown in Figure 3, the circle symbols represent the MGs, with the thickness of PMs at high-speed rotor different and low-speed rotor and the size of MGs being fixed with a 164 mm outer diameter. At first, the data are varied by the increased thickness of PMs at low-speed rotor, while the thickness of PMs at high speed is fixed. The data are then varied with the thickness of PMs at high speed increasing, while, at low speed, the thickness is fixed. The changed thickness of PMs influences the volume of PMs where the transmission torque increases as the total volume of PMs increases. For the square symbols data, the diameter of MGs also fixed with 164 mm outer diameter, while the thickness of pole pieces is fixed to 10 mm.  
The thickness of PMs at both high-speed and low-speed rotors is increased equivalently to observe the effect on transmission torque. From the observation, the transmission torque also increased and started to saturate at 100 Nm of transmission torque. For the diamond symbols data, the size of MGs is fixed at 200 mm outer diameter, and the thickness of PMs at both high-speed and low-speed rotors are also the same. The thickness of pole pieces is also the same as with previous data, i.e., 10 mm. By increasing the thickness of PMs, the transmission torque also increased and was higher than the MGs with the previous data, and it started to saturate at 140 Nm of transmission torque. Meanwhile the triangle symbols data are randomly designed MGs without a trend and a uniform increment in parameters. From the data analysis, it is observed that some of the MGs achieved a high transmission torque. This is due to a better flux distribution between PM that is resulting in higher torque transfer. The flux distribution is influenced by the size of the ferromagnetic iron in the  
Figure 2: Parameters of surface type of PM concentric magnetic gear.  
magnetic gear which is needed to be optimized to avoid saturation of magnetic flux. The saturation of magnetic flux occurs because of the limitation of magnetic flux density in the iron, which is around 1.6 to 1.8 Tesla. The saturation of magnetic flux affects the performance of MG, thereby reducing the transmission torque, especially when the thickness of PM is increased, but the thickness of iron at outer yoke, inner yoke, and pole pieces remain the same.  
From the obtained maximum points, a line which is named the Maximum Transmission Torque Line (MTTL) is created by connecting all the maximum points, as shown in Figure 3. The MTTL is the line of highest transmission torque value achieved at every total volume of PMs. The purpose is to have a reference in designing magnetic gears, using the total volume of PM corresponding to a specific torque that is suitable for its application. From the obtained MTTL, the relationship between the maximum transmission torque (\(T_{\rm 1s}\)) and total volume of PMs (\(V_{\rm pm}\)) is established, as in Equation (3).  
\[T_{\rm 1s}\ =\ 0.56V_{\rm pm} \tag{3}\]