➢Spur Gear（直齿圆柱齿轮）
Tangential load 切向力ຫໍສະໝຸດ Ft12T1 d1
Ft 2
Radial load Fr1 Ft1 tg Fr2
径向力
Normal load 法向力
Fn1
Ft
cos
Fn2
Nominal Torsion
T1
9.55 106
P1 n1
Nmm
kW r/min
Question: How to Judge the Axial Load Direction Acting on the Helical Wheel?
Principles of left or right hand (Driving（主动） Gear)
Determine the helical direction of driver gear teeth
Loads in mesh （啮合）
Force in mesh Friction force Accessional（附加的） force
Hypothesis（假设）:
•Concentration force acting on the midpoint of tooth width
•Ignoring（忽略） friction force between meshing teeth
Lubricating condition
Soft skin of teeth 软齿面（350HBW） ——收敛性点蚀
pitting
Only can be found in the enclosed gear boxes
Hard skin of tooth 硬齿面（>350HBW） ——扩展性点蚀
scoring and scuffing（胶合）
High speed, Heavy load, or Low speed ,Heavy load
plastic deformation
abrasion（磨损），pitting（点蚀），scoring and scuffing （胶合），plastic deformation（塑性变形）
3）Major influence factors of gear failures
➢ fluctuated（变化的） stresses； ➢relative sliding velocity（速度） of mesh teeth； ➢Materials and their heating treatment; ➢lubricating condition
Direction of loads Fig6-10 p191
ω
Driver Gear (主动轮-1）
➢Helical Gear（斜齿轮）
Ft1 2T1 / d1 Ft2 Fr1 Ft1 tgn / cos Fr2
Fa1 Ft1tg Fa2
Fn Ft /(cosn cos )
b
3. Use the GB as the basis for completing the design of the gears.
Chapter 6 Gears
1.Loads exerted on gear teeth
2.Failures of gears and design rules
3.Bending stress in gear teeth
2.Failures of gears and design rules
Fatigue failure occurs only on or in gear teeth
1) Bulk（体积） or body of gear tooth----tooth breakage 2) skin-deep（表面） of gear tooth
Put out your “right” hand and hold the axes, then make sure four fingers except the thumb（大拇指） to the direction of the rotation.
At last, your thumb points the direction of the axial（轴向）force.
Chapter 6 Gears
Objects of this chapter
1. Compute the forces exerted on gear teeth as they rotate and transmit power.
2. Describe suitable metallic（金属的） materials from which to make the gears, in order to provide adequate（适当的、足够的） performance for both strength and pitting（点 蚀） resistance（抵抗力）.
1）Bulk（体积） or body of gear tooth----tooth breakage
tooth breakage
2)skin-deep（表面） of gear tooth
abrasion
Opening Gear Transmission----No lubrication is used Enclosed（被装入箱子的） Gear Transmission---using lubrication
TRY BY YOURSELF!!
➢Straight Bevel Gear（直齿锥齿轮）
Ft
2T1 dm1
Fr1 Fttg cos1 Fa2
Fa1 Fttg sin1 Fr2
Fn
Ft
cos
Direction of Axial Load: point to large transverse plane
4.Contact stress on gear teeth 5.Choice of spur gear parameters（参数） 6.Structure（结构） design of wheels and gears
lubrication
7.CAD in design of gear pair
1. Loads exerted on gear teeth