Strength Of Helical Gear

Introduction:

In order to find the strength of helical gears, a modified Lewis equation is used.

Strength of Helical Gears

In helical gears, the contact between mating teeth is gradual, starting at one end and moving along the teeth so that at any instant the line of contact runs diagonally across the teeth.Therefore in order to find the strength of helical gears, a modified Lewis equation is used. It is given by

W_T = (σ_o × C_v) b.π m.y'

where W_T = Tangential tooth load,
σ_o = Allowable static stress,
C_v = Velocity factor,
b = Face width,
m = Module, and
y' = Tooth form factor or Lewis factor corresponding to the formative or virtual or equivalent number of teeth.

Notes :

1. The value of velocity factor (Cv) may be taken as follows :

2. The dynamic tooth load on the helical gears is given by

where v, b and C have usual meanings as discussed in spur gears.

3. The static tooth load or endurance strength of the tooth is given by

W_S = σ_e.b.π m.y'

4. The maximum or limiting wear tooth load for helical gears is given by

where D_P , b, Q and K have usual meanings as discussed in spur gears.

In this case,  

where φ_N = Normal pressure angle.