Design of Helical Gears.pptx

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: I t 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 P c . 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 P n . 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, P n =P c C os α Facewidth of helical gears:

8. Facewidth of H elical gears: Overlap = Pc = b tan α The normal tooth load (W N ) has two components ; one is tangential component (W T ) and the other axial component (W A ), as shown in Fi g . The axial or end thrust is given by W A = W N sin α = W T 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 = 15 to 25 Helix angle , α = 20 to 45 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

11. Problems