14.4.5.6. Gears - Modification (External, Internal, Planetary)

The amount of tooth modification can be determined in the modification tab. The tooth modification may be a good method to increase the contact area and distribute a contact force. The modification is managed by the left flank and right flank separately .

Figure 14.144: Modification tab in designer

Figure 14.145: Parameters in the Modification tab

Parameter	Description	Dimension (Range)
1. Profile Crown	Use to set the amount of profile crown. This value must be entered in units of 1/1000 of the system unit (for example, when the unit system is MMKS, if the input value is 100, this is calculated as 0.1mm).	Length
2. Profile Slope	Use to set the amount of profile slope. This value must be entered in units of 1/1000 of the system unit.	Length
3. Tip Relief	Use to set the amount of tip relief. This value must be entered in units of 1/1000 of the system unit.	Length
4. Lead Crown	Use to set the amount of lead crown. This value must be entered in units of 1/1000 of the system unit.	Length
5. Lead Slope	Use to set the amount of lead slope. This value must be entered in units of 1/1000 of the system unit.	Length
6. A point	Use to set the modification reference point (A) Refer to Equation 14–4 ~ Equation 14–11.	N/A
7. B point	Use to set the modification reference point(B) Refer to Equation 14–4 ~ Equation 14–11.	N/A
8. Z point	Use to set the modification reference point (Z). Refer to Equation 14–4 ~ Equation 14–11.	N/A
9. Select Gear	Select the gear to check.	N/A
10. Type of modification	Select the modification type.	N/A
11. Side of gear flank	Select the flank to check.	N/A
12. Position of modification	Select the position to check.	N/A
13. Chart of modification	Display the modification. X - axis is an amount of modification. Y- axis is a location number of involute.	N/A

Figure 14.146: Definition of profile modification

Figure 14.147: Modification definition

The reference points of A, B, and Z can be calculated using the following equations.

When using an external gear
(14–3)
(14–4)
(14–5)
(14–6)
(14–7)
(14–8)
(14–9)
(14–10)
(14–11)
When using an internal gear
(14–12)
(14–13)
(14–14)
When using a ring gear, a_w and z₂ have a negative value.
(14–15)
(14–16)
(14–17)
(14–18)
Where .
(14–19)
(14–20)
(14–21)
(14–22)
(14–23)
(14–24)

Where,

m_t: Gear module (transverse)

m_n: Gear module (normal)

d_a1: Outside diameter of gear 1

d_a2: Outside diameter of gear 2

d_b1: Base circle diameter of gear 1

d_b2: Base circle diameter of gear 2

d_wp1: Pitch circle diameter of gear 1 (engaged)

d_wp2: Pitch circle diameter of gear 2 (engaged)

α_n: Pressure angle (normal)

α_t: Pressure angle (transverse)

α_wt: Pressure angle (engaged)

a_w: Center distance

Figure 14.148: Schematic of reference point

Alternatively, for external, internal and single pinion planetary gears, micro geometry can be modified according to ISO 21771. This method can be modified by activating Setting > Labs > Advanced Gear Geometry (see below).

Figure 14.149: Enable Advanced Gear Geometry for an external gear

Figure 14.150: Modification tab in designer when Advanced Gear Geometry is enabled

Note: In the Profile Crown, Profile Slope, Tip Relief, Lead Crown, Lead Slope and Lead Relief fields, the entered value must be divided by 1000 in reference to the current unit system.

Figure 14.151: Parameters in designer Modification tab for advanced gear geometry

Parameter	Description	Dimension (Range)
1. End Diameter at Tip (D_Ca)	Use to set the end diameter (tip)	Length
2. End Diameter at Root (D_Cf)	Use to set the end diameter (root)	Length
3. End Relief Length1 (L_C1)	Use to set the amount of end relief Length1	Length
4. End Relief Length2 (L_C2)	Use to set the amount of end relief Length2	Length