Gearing Flashcards
What does hearing refer to?
A system of moving parts
What is a gear train?
Made up of a number of gears
3 types of gears
Driver
Driven
Idler
What are the 4 primary functions of gears?
Transfer drive
Change direction of rotation (same plane)
Change direction of rotation (different angles)
Change speed of rotation
2 types of cut on gears
Straight
Helical
Where are straight cut gears usually used?
Pumps
What are straight cut gears prone to?
Wear
Single point loading
Helical cut gears can produce?
Heavy axial loading
Two helical cut gears inherently want to what?
Drive apart
How do we stop helical gears driving apart?
Introducing an opposing cut to ensure gears remain in mesh
Two types of gears used in helicopters?
Spur
Bevel
When are internally toothed spur gears used?
Change of speed but not axis of drive
When are externally toothed spur gears used?
Change of speed when shafts are parallel
What teeth in Spur gear?
Straight & helical
When are bevel gears used?
Drive transmitted at an angle
Teeth used in a bevel gear?
Straight & helical
What is a hypoid gear?
When axes of shaft do not intersect
Purpose of reduction gear train?
Keep rotor speed in efficient operation
Without reducing peak performance of engine
Epicyclic gear
What makes up epicyclic reduction gear train
Spur sun wheel driven by main
Driving three even spaced planets
Plants mounted on planet carrier
Planets rotate independently
Plants mesh with annulus (internally toothed)
Epicyclic gears achieve what?
Smaller size for gear box
Two types of gear profile
Involute
Convolute/Conformal
Involute gear form
Driver & driven same
Pros of involute
Easier to manufacture
Disadvantage of involute
Low surface area contact, high point loads
Pros of conformal gears
Has area contact enabling higher loads
What is backlash?
Space to allow for lube & expansion
How is gear ratio calculated?
Driven/driver
What is a hunting tooth ratio?
Stops same teeth meshing together on each revolution. To evenly spread wear
Maintenance on gears?
Correct level & type of oil
Ensure oil is clean (filter change @ intervals)
Monitor backlash at intervals
Monitor oil at intervals (detect wear particles)
