Example3 Cogging Torque of Axial Gap Type Motor

General

Axial gap type motor is analyzed.
Axial gap type motor consists of opposing disc type rotor and stator.
Cogging torque is analyzed which is incurred by the rotor’s rotation while no electricity is applied to the coils.
Analysis function for axial gap motor is applied.
The cogging torque and the magnetic flux density are solved.
Unless specified in the list below, the default conditions will be applied.

Analysis Conditions

Item	Setting
Solver	Magnetic Field Analysis [Luvens]
Analysis Space	3D
Analysis Type	Transient Analysis
Unit	mm
Options	Select Rotating Machinery. [Conversion] Select Partial Model. Number of Divisions of the Whole Model: 4 Select Convert the result to the whole model and output it.

The Rotating Machinery tab is set as follows.

Tab	Setting Item	Setting
Rotating Machinery	Rotational Movement	Select Constant Velocity Number of Rotations: 1800[r/min] Rotor’s Initial Rotation Position: 0[deg]
	Gap Type	Axial Gap
	Number of Slide Mesh Divisions	Circumferential Division Angle: 1.0[deg] Rotation per Step: 1[mesh] Number of Slide Mesh Layers: 3
	Location of Slide Mesh	Deselect Automatic calculation Rotor Type: Outer Rotor [Gap Radius] Inner: 110×10^-3[m] Outer: 112×10^-3[m] [Gap’s Coordinates in Axial Direction (Z Coordinate)] Top Side of Upper Gap: 52×10^-3[m] Bottom Side of Upper Gap: 50×10^-3[m] Top Side of Lower Gap: -50×10^-3[m] Bottom Side of Lower Gap: -52×10^-3[m]
	Division Size of Slide Mesh in the Axis Direction	Divide at uniform interval with specified mesh size 10.0[mm]

Set the Mesh Tab as follows.

Tab

Setting Item

Setting

Mesh

Meshing Setup

Automatically set the general mesh size: Deselect

General mesh size: 5[mm]

Ambient Air Creation

Select Create ambient air automatically

Ambient Air Scale: 1.2

The Transient Analysis tab is set up as follows.

With the settings as below, number of steps is 90, circumferential division angle is 1.0[deg], and rotation per step is 1[mesh], the rotation up to 90 degrees (=90*1.0*1) is analyzed.

Tab

Setting Item

Setting

Transient Analysis

Time step

Automatic

Table

Number	Calculation steps	Output steps
1	90	1

Graphical Objects

A rotor core and coils are placed between stator cores and permanent magnets.

By utilizing the symmetry of the analysis model, it is made to be a quarter model.

“Ambient Air Creation” is selected.

It is assumed that coil1, 2, and 3 are made of fine copper wires which will have little effect of induced current. So, “No” is selected for the Options of Induced Current.
If “Yes” is selected, the loss by induced current will impact the analysis and correct cogging torque will not be obtained.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
34/Solid	coil1	Cu
35/Solid	coil2	Cu
36/Solid	coil3	Cu
33,37,38/Solid	st_core	core
20,31/Solid	mag1	mag
19,30/Solid	mag2	mag
23,32/Solid	rt_core	core

The material properties are set up as follows:

Body Attribute Name	Tab	Settings
coil1	Current	Induced current: deselect
coil1	Stator/Rotor/Air	Stator
coil2	Current	Induced current: deselect
coil2	Stator/Rotor/Air	Stator
coil3	Current	Induced current: deselect
coil3	Stator/Rotor/Air	Stator
mag1	Direction	Vector: X=0, Y=0, Z=1
mag1	Stator/Rotor/Air	Rotor
mag2	Direction	Vector: X=0, Y=0, Z=-1
mag2	Stator/Rotor/Air	Rotor
rt_core	Stator/Rotor/Air	Rotor
st_core	Stator/Rotor/Air	Stator

The material properties are set as follows.

Material Name

Tab

Properties

Conductivity

Conductivity Type: Conductor

Conductivity: 5.977×10^7[S/m]

mag

Relative permeability

Material Type: Permanent Magnet

Magnet

Magnetization Characteristic Type: Linear

Magnetization Strength: 0.5[T]

Relative Permeability: 1.05

core

Permeability

Magnetization Characteristic Type: Select B-H curve

B-H Curve Table

Magnetic Field [A/m]	Magnetic Flux Density [T]
0	0
58	0.42
90	0.8
180	1.19
380	1.37
1100	1.48
2000	1.55
3000	1.608
11000	1.81
20000	1.91

Boundary Conditions

Symmetric period boundary is set.

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Settings
Symmetry	Symmetry/Continuity	Periodic	Rotation Period (1 period)

Results

The distribution of the magnetic flux density at the rotation angle of 0[deg] is shown below.

The wave of cogging torque is shown as follows.

See other Magnetic Analysis (Transient Analysis) examples.