6.9 Flashcards
Why are spur gears used ?
- Increase or decrease speed of a device
- Multiply torque by transmitting power and motion from one shaft to another.
( spur gears are noisy )
Spur gears connect parallel shafts only.. true or false ?
True
When two spur gears of different sizes mesh together, what’s the larger and smaller gear called ?
Larger gear - wheel ( spur )
Smaller gear - pinion
Whats the two spur gears ?
External spur gears - used when shafts are parallel to each other
Internal spur gears - Maintains diameter
What gear is a modification of a spur gear ?
Helical gears - carry heavier loads, quiet
Whats the Two types of helical gears ?
Single helical - transmit more power than straight cut gears
Double helical - transmit more force
Where are bevel gears used ?
between intersecting shafts
What does curved teeth on bevel gear allow it to do ?
Run quieter
Carry greater loads
What does hypoid gears require for them to not slide ?
Extreme pressure lubricant
( quieter and smoother than bevel gears )
What does worm gears connect ?
Non-intersecting shafts
( worm gears offers high reductions in single steps )
What makes worm gear highly inefficient to other gears ?
Large sliding movement in teeth
Where is worm gear used ?
Flap control systems.
( places which have to be driven in both directions ( up and down )
Why is a rack and pinion gear system used ?
To transmit motion between rotating spur gears and toothed rack.
What motions does a rack and pinion gear convert ?
Rotational to linear
Where is rack and pinion gears used ?
Leading edge flaps
What must be different on either driven gear or drive gear to gain a mechanical advantage ?
Number of teeth must be different.
Whats the calculation to find gear ratio
Number of teeth on driven gear divided by number of teeth on drive gear
Note : drive gear rpm is 2x driven gear rpm
Where are idler gears used and why ?
Between two other gears to :
1. To link two distant gears
2. To make output gear rotate same direction as input gear
( presence of idler gear makes no difference to ration speed )
Whats the purpose of a reduction gear ?
To allow both engine and prop to operate within their most efficient speed.
What gear is used as a reduction gear ?
Epicyclic ( planet ) gear
What gears is a planet gear made from ?
- Sun gear
- Planet gear
- Ring gear ( fixed )
What happens if the gears teeth are meshed to highly and to low ?
High - load is transmitted to small portion of teeth causing them to brake.
Low - teeth cannot be lubricated.
Whats the two most important factors when it comes to mating two gears ?
Meshing and patterns.
What does gear backlash ?
Clearance between teeth and meshing point.
( prevents over heating and allows for lubrication )
What is a belt ?
Flexible material used to link or drive two or more rotating shafts
( assembled parallel )
How can a belt drive change the speed of rotation ?
Using different sized pulleys
Whats the two belt types ?
- Friction drive belts
- Positive drive belts
Whats 1 advantages of using flat belts ?
- Due to being driven off friction it eliminates the need for high tension, reducing shaft and bearing loads.
( flat belts are not advisable for high outputs at high speeds as the belt could slip.
Whats the V-shape on a V-belt allow ?
Allows fast moving belts to stay in grooves better than it is to keep a flat belt on a pulley
What good features does a V- ribbed belt and V- belt have ?
V-ribbed belt - ribs ensure belt tracks properly
V-belt - runs efficiently and can be ran at high speeds
When would you use a timing belt ?
Where exact synchronisation between driver and driven shaft is required.
What can cause a drive to be noisy ?
- If belt teeth don’t match with pulley grooves.
- If belt wears from ratcheting.
What differs a V-belt pulley to other types of pulleys ?
V-belt pulleys have deep grooves which guide and gain traction
What advantages does a synchronous pulley have ?
- Non-lubricated
- Non-slip
- Long lives
- Quiet
Why would you use a stepped or cone pulley drive ?
Where different operational speeds can be produced by changing belt to a different pulley size.
What does a chain engage with to transmit power ?
Sprocket
What’s the use of a chain ?
To transmit motion between two sprockets
What is the sprocket called on the driven shaft ?
Driver sprocket.
Whats the two types of chains ?
- Leaf chain
- Roller chain
Why are leaf chains not used as much as roller chains ?
As leaf chains need frequent lubrication and can only be used for low speed applications.
What does leaf chains run over rather than sprockets ?
Sheaves
Whats an advantage for chain drives ?
Don’t slip because of teeth.
Whats a disadvantage for chain drives ?
There heavy and noisy and expensive
