Design of helical gears

1. Design of Helical Gear
Presented by
AJAY KUMAR REDDY K
ASSISTANT PROFESSOR
Department of Mechanical Engineering

2. Learning Objectives
• Understand the terms used in helical gears
• Proportions of helical gears
• Strength of helical gears
• Dynamic load on gear tooth
• Beam and wear strength of helical gears

3. Learning outcomes
By the end of this topic , you will be able to :
• Understand various terms used for helical gears
• Analyze the design of helical gear
• Proportions used in the design of helical gear
• Beam strength of the helical gear
• Wear strength of the helical gear

4. Introduction
• Helical gears are used for transmitting power between two
parallel shafts.
• Gears which have the teeth with inclined to the axis. Hence for
the same width, their teeth are longer than spur gears and have
higher load carrying capacity.
• The teeth on helical gears are cut an angle to the face of the
gear.
• When two teeth on a helical gear system engage , the contact
starts at one end of the tooth sand gradually spreads as the
gears rotate, until the two teeth are in full engagement. This
gradual engagement makes helical gears operate much more
smoothly and quietly than spur gears.
• For this reason, helical gears are used in almost all car
transmission system.

5. Advantages of helical gear
• Silent operation: In a helical gear train, the gear teeth engage a little
at a time rather than the entire face at once. So that it causes less
noisy power transfer in case of helical gears.
• Non- parallel shafts: Helical gears can be used for transferring power
between two non parallel shafts. But the efficiency will not be more
effective.
• Strength: While comparing spur gear along with the helical gear may
considering the same tooth size(module) and equivalent width,
helical gears can handle more load than spur gears because the
helical gear tooth is effectively larger since it is diagonally positioned.
On the other hand helical gear should be considered for smooth high
power applications.

6. Disadvantages of helical gear
• Efficiency of helical gear is less because helical gear trains have
sliding contacts between the teeth which in turns produce axial
thrust of gear shafts and generate more heat. So, more power loss
and less efficiency.

7. Terms used in Helical Gears
• Helix angle: A constant angle which is made by the helices with the axis of
rotation.
• Axial pitch: It is the distance between the parallel to the axis, with similar
faces of adjacent teeth. And also it is the same as circular pitch and is
therefore denoted by Pc. The axial pitch may also be defined as the circular
pitch in the plane of rotation or the diametral plane.
• Normal Pitch: It is the distance between the similar faces of adjacent along
a helix on the pitch cylinders normal to the teeth. It is denoted by Pn. The
normal pitch may also be defined as the circular pitch in the normal plane
which is a plane perpendicular to the teeth. Mathematically. Normal pitch,
Pn=Pc Cosα
• Facewidth of helical gears:

8. Facewidth of Helical gears:
• Overlap = Pc = b tan α
• The normal tooth load (WN) has two components ; one is tangential
component (WT) and the other axial component (WA), as shown in
Fig. The axial or end thrust is given by WA = WN sin α = WT tan α

9. Proportions of helical gear
Basic proportions for the helical gears are not standardized, yet the following
are recommended by American Gear Manufacturer’s Association(AGMA)
• Pressure angle in the plane of rotation, φ= 150 to 250
• Helix angle , α = 200 to 450
• Addendum = 0.8m(Maximum)
• Dedendum = 1m(Minimum)
• Minimum total depth = 1.8 m
• Minimum clearance = 0.2 m
• Thickness of tooth = 1.5708 m
Equivalent number of teeth:

10. Strength of Helical Gears

12. Problems