Overview

Magnet coupling has two rotors, the driving side and the passive side. Unlike magnetic gears, the driving side and the passive side rotate synchronously. If torque exceeds the allowable torque, connection from the driving side to the passive side will slip, causing torque decoupling. The allowable torque is evaluated with the maximum value of the holding torque that keeps the relative positional relationship between the driving side and the passive side.
This document, presents an analysis for finding holding torque and an analysis for transient response during torque decoupling.

Holding Torque

In general, the holding torque has a periodicity of two poles (90 deg), and maximum torque is reached when the relative position is shifted by 1/4 pole (22.5 deg). When the passive side is fixed and the driving side is rotated, relative position is changed and the holding torque waveform for 90 deg is obtained.
Fig. 1 shows the holding torque for 90 deg when the inner part is rotated. Peak torque at 22.5 deg is about 16.2 Nm.

Starting Response and Delay Angle

Load torque given to the passive side is based on the supposition of load occurring from circumstances such as fluid in the pump. Also, load torque dependency on rotation speed is considered, and the equation shown in Fig. 2 is used to assign the equation of motion as the relaxation factor.
The rotation speed of the passive side is displayed in Fig. 3 for when the load torque assigned to the passive side is 10 Nm, 14 Nm, 16 Nm, 16.5 Nm, 17 Nm, and 18 Nm. The rotation speed of the driving side is also displayed in the figure as the “Reference” line. Notice that the passive side is able to follow the rotation of the driving side until a load torque of 16.5 Nm is reached. Values of 17 Nm and 18 Nm do not follow the rotation, and the sides become decoupled.
Fig. 4 shows the delay angle of the passive side at the time the driving side makes one rotation. The delay angle when the load torque is 16.5 Nm is about 22 deg. For load torque of 17 Nm and 18 Nm, it can be seen that slippage is about 90 deg.