Transmissions Flashcards
What is the main functionof belt drives, chain drives and gears?
To change or move torque and/or speed
Friction based transmissions
- Flat belt drive
- V-belt drive
Form based transmissions
- Timing belt drive
- Gear drive
- Sprockets
6 types of gears
- Spur
- Helical
- Bevel
- Worm
- Hypoid
- Planetary
Benefits and drawbacks of belt drives
+ Simple
+ Inexpensive
+ Doesn’t require acually aligned shafts
+ Helps protect the machinery from overload
+ Damps and isolates noise and vibration
+ No need for lubrication and minimal maintenance
+ High efficiency
+ Allows shafts far apart
- Angular-velocity ratio may not be constant due to slip
- Might need adjustments due to wear
- Requires pre-tensioning (v-belts and flat belts)
What is crowning?
The removal of a slight amount of the tooth from the center on out to the reach edge. It is done so that the belt can self-center.
What is end relief?
The chamfering of both ends of tooth surface.
Four types of v-belts
- Standard
- Multiple
- Cogged
- Poly
Name four belt tensioning methods
- Constant distance between shafts
- Constant radial load
- Tensioner pulley
- Self tensioning
Benefits and drawbacks with the method constant distance between shafts
+ Simple
+ Equally good for both directions
+ Belt tension doesn’t increase with speed
- Transmittable torque decreases if speed increases
- Belt tension decreases over time, might need after-adjustments
Benefits and drawbacks with the method constant radial load
\+ No need for after-adjustments \+ Works for both directions \+ Transmittable torque independent of speed - Complicated - Expensive - Belt can be damaged by high speeds
Benefits and drawbacks with the method tensioner pulley
+ No need for after-adjustments
+ Transmittable torque independent of speed
+ Increases the wrap angle
- Belt tension increases with speed
- Reversed torque direction will give sliding
- Tensioner pulley gives extra load on the belt
Benefits and drawbacks with the method self-tensioning
\+ No need for after-adjustments \+ No risk for sliding \+ Never more belt forces than needed - Complicated - Reversed torque direction impossible - No protection against overload of torque and velocity
Chains and timing belts can transmit…
1) Power between distant shafts
2) More power than v-belts but less than gears
Comparing timing belts and chains
- Chains can transmit much higher forces -> smaller sprockets can be used
- Timing belts can run faster
- Chains are noisier
- Chains need lubrication
- Chains can be disassembled
