Design

Prof. Samy J. Ebeid ١

Helical Gears

١Helical Gears

Helical Gears

٢Helical Gears

Design

Prof. Samy J. Ebeid ٢

٣Helical Gears

Peripheral Speed & Speed Ratio

100060100060

2211

x

ND

x

NDv

ππ==

2

1

1

2

1

2

N

N

Z

Z

D

Du ===

٤Helical Gears

Design

Prof. Samy J. Ebeid ٣

Helical Gear Geometry

٥Helical Gears

Helical gears are more efficient than spur gears:-Two pairs of gears are in engagement.

-The line of contact is inclined to the root of the teeth.

-The loading diagram is non-uniform and the teeth behave

as plates rather than cantilever beams.

-The teeth are thicker at the dangerous section.

٦Helical Gears

Design

Prof. Samy J. Ebeid ٤

Advantages of Helical Gears

٧Helical Gears

Helical Gear Planes

٨Helical Gears

Design

Prof. Samy J. Ebeid ٥

٩Helical Gears

PCD

Normal Plane AA

Section AA

١٠Helical Gears

Design

Prof. Samy J. Ebeid ٦

Parameter Pinion Gear

Number of teeth Z1 Z2

Diameter D1 D2

Module (=d/z) m m

Normal Module mn mn

mn = m. cos γγγγ

Helix angle β β

Addendum m m

Dedendum 1.2m 1.2m

RPM N1 N2

D = m . Z

Normal pitch = Pn = Pt . cos β١١Helical Gears

pc = circular pitch

pn = normal pitch

td = tooth displacement or

advance (= 0 for spur)

b = face width of gear rim

b1 = face width of tooth

γ = helix angle

١٢Helical Gears

Design

Prof. Samy J. Ebeid ٧

Virtual or Formative Number of Teeth

The Virtual Number of Teeth is defined as the number

of teeth that could be generated on the surface of a

cylinder having a radius equal to the radius ofcurvature ρρρρ at a point at the tip of the minor axis (of

size D) of an ellipse obtained by taking a section of the

gear in the normal plane.

zf = z/cos3γγγγ

Z=Actual

number of teeth

The zf is used in specifying

the cutter.

mn = m * cos γγγγ

D= m * zmn is

standardized١٣Helical Gears

Helical Gear Geometry

Plane normal to teeth

١٤Helical Gears

Design

Prof. Samy J. Ebeid ٨

z teeth

zf = z/cos3γγγγ

١٥Helical Gears

γ=0 : spur gear

γγγγ

١٦Helical Gears

Design

Prof. Samy J. Ebeid ٩

Right and Left Hand Gears

١٧Helical Gears

١٨Helical Gears