6.9 Transmissions Flashcards
What is one of the most popular precision gears?
Spur
What teeth do spur gears have?
Straight cut, internal or external.
What are the larger and smaller wheels of spur gears called?
Larger is spur and smaller is pinion.
Where are external spur gears used?
Change of speed is required and the shafts are parallel.
Where are internal spur gears used?
When a speed change is required whilst maintaining an overall minimum diameter.
What is the benefit of spur gears with helical cut teeth?
Carry heavier loads at higher speeds, quieter and smoother.
Why can helical spur gears carry more load?
They have more teeth = more surface area with which to carry load.
What is the maximum angle of helical cut teeth?
20 degrees
What is a herringbone gear?
Double helical gear used for larger forces.
What are bevel gears?
Gears that meet at 90 degrees.
What is the theoretical point of intersection called on bevel gears?
Apex
What type of bevel gear is better in most aspects?
Spiral bevel.
What is a hypoid gear?
A variation of the bevel gear, however they suffer from heavy sliding contact and need extreme pressure lubricant.
How does a worm gear work?
Consists of the worm screw that drives a worm gear.
At what reduction would a worm wheel be unable to drive the worm screw?
20:1
How is the speed ratio of worm gears calculated?
Dividing the number of thread starts on the worm screw into the number of teeth on the worm wheel.
When is no mechanical advantage gained?
If the drive and driven have the same number of teeth.
What is the purpose of an idler gear?
Used between two gears to either make the input direction the same as the output of fill a gap between two gears.
Does the idler gear change the speed ratio?
No
How can the direction of rotation be worked out in a gear train?
By counting them from the input-
even- same rotation
odd- opposite
What is the aim of a reduction gearbox?
Lower the speed but maintain torque.
What is backlash?
Describes the clearance between the teeth allowing for a film of lubrication.
What would excessive backlash be a sign of?
Worn gearing.
What types of belt are there?
Friction drive or positive drive.
