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
The rule of thumb for chordal action / polygone effect
Use at least 17 teeth. The higher amount of teeth, the less speed variation.
What kind of lubrication fluid is used for chain drives?
Petroleum based (similar to engine oil)
Methods of lubrication
- Manual or drip
- Bath or disc
- Oil steam
