6.9 Transmissions✅(2) Flashcards
What are the benefits of gears used in conjunction with bearings and shafts
- transmit power and increase or decrease rotational speed
Which gear is the most popular type for precision cylindrical gears
Spur gears
What is the advantage of a spur gear
- easy to manufacture
What is the disadvantage of a spur gear
- noisy in operation
When 2 spur gears of different sizes mesh together, what is the larger gear called
- wheel (spur)
When 2 spur gears of different sizes mesh together, what is the smaller gear called
- Pinion
What is a spur gear
- straight teeth parallel to the shaft’s axis and connect parallel shafts only
In a spur gear, what is the external teeth used for
- change of speed is required, and the shafts are parallel to each other
In a spur gear, what is the internal teeth used for
- when a change of speed is required whilst maintaining a overall minimum diameter
Advantage of helical cut (spur gear)
- carry heavier loads at higher speeds
- run more smoothly and quietly
Where are bevel gears used between
- intersecting shafts and can be designed for any angle of intersection
example of a bevel gear
main drive shaft of an aircraft engine to drive the accessory gearbox
Advantages of bevel gears
- quieter and smoother in operation
- carry greater loads
Is hypoid gears or spiral bevel gears more quieter and smoother in operation
- hypoid gears
- Which gear suffer from heavy sliding contact and require extreme pressure lubricant
hypoid gears
Advantages of worm gears
- quiet
- carry heavy loads
worm gears are inefficient compared to other gears due to the large sliding movement of their teeth (T or F)
- T
What does a worm wheel offer in a worm gear
- offer high reductions in single steps
Where would a worm gear be used
- aircraft flap control systems
What is a rack and pinion system used to transmit
motion between a rotating spur gear and linear toothed rack
What does rack and pinion system convert
rotational motion into linear motion
Where would a rack and pinion be often used on
- leading edge flaps for extension and retraction
A gear is a toothed wheel that, when operated, transmits motion from one shaft to another (T or F)
T
Which gear is the small gear in a mechanical advantage system
drive gear
Which gear is the large gear in a mechanical advantage system
driven gear
What is the gear ratio formula
number of teeth on driven gear/number of teeth on drive gear
How do you calculate speed ratio
input speed/speed ratio
What are Idler gears also named as
- Intermediate gears
Where would you use a idler gear
- Used between 2 gears
Does the presence of an idler gear make a difference to the ratio of speed between input and output
no
A reduction gear is an arrangement by which an input speed can be lowered to obtain a slower output speed with the same or equivalent output torque (T or F)
T
What is primarily used to reduce gearing in aircraft engines
Epicyclic, or planetary gears
What is backlash
clearance between gear teeth at the meshing point
What does excessive backlash indicate
worn gearing
What is a belt drive used for
- change the speed of rotation
What is a belt
- loop of flexible material used to mechanically link or drive 2 or more rotating shafts
What is a friction drive belt
- relies on friction between belt and pulley to transmit power
- requires correct tension
What is a positive drive (synchronous) belts
- relies on teeth engagement on belt with grooves on pulley
What are modern day belts made out of
- nylon
- aluminium with reinforced, rubberised fabric
Flat belts are not advisable for high outputs at high speeds (T or F)
T
Advantages of V-belts
- low cost
- easy installation
- wide range of sizes
What is the operational advantage of a V-belt
- wedging action into the pulley groove
When were synchronous belts first introduced
1940
What are synchronous belts also known as
timing belt
What are V belt pulleys solely used for
- transmitting power between 2 parallel axis
What are leaf chains
- simple form of steel chains, consisting of link plates and pins
- very strong
Advantage of chain drives
chain cannot slip on the sprocket because of the teeth
Disadvantage of chain drive
- heavy, noisy, more expensive than belt pulley system drive system
- Used where slipping must not occur
How is a sprocket locked to the shaft
- by the use of a keyway or grub screw
Chains are only used where slipping must not occur (T or F)
T
What is a sprocket
Toothed wheel that fits onto a shaft
Leaf chains must be used for low or high speed applications?
Low speed
Leaf chains or chain drive cannot slip?
Chain drive as they have teeth
Flat belts are not advisable for high outputs at high speeds (T or F)
T
