General Gear Meshing

Gear Parameters

Gear Rotational Axis Vector

Specify the direction of the axis of rotation of the drive gear in the laboratory reference frame, in coordinates.

Figure 6.889 - Rotational axis vector- General Gear

Add a Gear

This is used to assign the type of the gear. Choose between Internal Gear and External Gear.

The control parameters associated with Internal Gear/ External Gear are below.

Gear Name

Provide the gear name under Gear Name in Gear 1 list.

Gear Center

Provide the center of gear rotation in coordinates, also the center of the gear container cylinder. Refer Figure 6.889.

Gear Surfaces

This is used to assign the gear as follows:

Select the gear1 surface under CAD Surfaces in the Geometric Entities Panel.
Click Add Surfaces icon to the right of Gear Surfaces in the Properties Panel.

Outer Surface Type

Template requires input for outer surface of each gear. User can specify the outer surface by following options.

By Radius: Provide radius of the outer surface including tip gap.
By Tip Gap: Provide tip gap size.
By CAD Input: In this option, user need to import the outer surface of each gear with tip clearance, as shown in Figure 6.885.

Figure 6.890 - Outer Surface Type

Number of Teeth

Specify the number of repeating geometry unit (gear teeth) on the gear.

Helical Gear

Select Yes to model helical gear and specify corresponding parameters.

The template supports two different Helical Definition types:

Figure 6.891 - Helical Gear

Guide Points Type

Guide Points are points that stay relatively stationary to the gear (i.e. rotate with the gear) during the gear movement. Guide Points prevent points moving from one gear tooth to the next gear tooth, therefore ensuring the positivity of volume in helical gear mesh. This feature has three options. Use Feature Angle, Use Extrema and Custom.

Figure 6.892 - Guide Points Type

Use Feature Angle: Set any corner points, where the angle is greater than the set value as a guide point. Most common option for angular gear shape.
Use Extrema: Use the points at the local maximum radius as guide points, can be used for smooth shaped gear/rotor.
Custom: Find the nearest points on the gear from each point entered by the users and use them as guide points. Meanwhile, repeat the points N times around the gear and define them as guide points (N being the number of gears set by the user). The user must input the guide point with respect to the lower outline shape of gear in case of a helical gear.

Viscous Layer Thickness

It is the total thickness of viscous layer. Figure 6.893 shows the viscous layer thickness with 25 micron and Figure 6.894 shows the viscous layer thickness with 100 microns.

Figure 6.893 - Viscous Layer Thickness – 25 Micron

Figure 6.894 - Viscous Layer Thickness – 100 Micron

Number of Layers

Specify number of cells (not nodes) in the viscous layer. Figure 6.895 shows 2 layers in the viscous thickness and Figure 6.896 shows 4 layers in the viscous thickness.

Figure 6.895 - Number of layers - 2

Figure 6.896 - Number of layers - 4

Mesh Reference Gear

By default, this is selected as Yes for first gear.

Gear Mesh Size

This allows to control the resolution of the mesh created in the gear chamber as:

Template requires input for outer surface of each gear. User can specify the outer surface by following options.

Coarse
Medium
Fine
User Defined

Figure 6.897 - Gear mesh size

Figure 6.898 - Gear mesh sizes

Specify Total Rotational Angle

Specify the total rotation angle between bottom and top surface (axial direction). The value is signed, it is positive when the rotation direction is the same as what is defined by the right-hand rule and the rotational axis vector.

Calculation of Total Rotational Angle

Pick one feature in the gear teeth, as shown Figure 6.899.
Mark two points at top and bottom surface for the same feature. Refer Figure 6.900.
Then, from top view, connect two points to the center using two lines and measure the angle between the lines, i.e. “Total Rotation Angle”. Refer Figure 6.901.
From bottom to top, if rotated in counter-clockwise, the angle is positive. Otherwise, the angle is negative.

For each pair of helical gears, the total rotational angle must have opposite sign. One is Positive and other one is Negative.

Value of Total Rotational angle multiply by the number of teeth is constant.

Example: In a pair of two meshing Helical gears, if one gear contains 10 teeth with +10° total rotational angle and other gear contains 20 teeth, then total rotational angle for other gear must be

Figure 6.899 - 3D view

Figure 6.900 - Top view

Figure 6.901 - Total Rotational angle

Specify Helix Angle

This allows to specify the angle between the gear teeth axial inclination and the gear axis. During mesh generation, the Helix Angle (see, Figure 6.902) is used to specify the correct slant of the rotor whereas, the CAD Surfaces are used as bounds for the mesh to obtain a water-tight volume.

Figure 6.902 - Helix Angle

The control parameters associated with User Defined (see, Figure 6.903) are:

Circumferential Points Per Gear: Corresponds to the number of cell nodes in the rotational direction along the circumference of the gear chamber. The number of control cells in this direction is shown in Figure 6.903. Default is 40.
Radial Points: Corresponds to the number of cell nodes in the radial direction from the center to the edge of the gear chamber. The number of control cells in this direction is shown in Figure 6.903. Default is 7.
Axial Points: Corresponds to the number of cell nodes in the axial direction from the bottom to the top of the gear chamber. The number of control cells in this direction is shown in Figure 6.903. Default is 30.

Figure 6.903 - User defined mesh size - Gear

Once the parameters for meshing are defined, click Build General Gear Mesh in the Geometry Tab of the Properties Panel. The general gear mesh is created and added under Built Meshes, and the corresponding Volumes are generated in the Geometric Entities Panel. Also, General Gear module is added to the Model Panel.