Chap 10: Gear Drive Flashcards by Learning Spree

gear drives vs belt and chain drives comparision

gear drives: more efficient and more compact
but costly and not easily maintainable

belt and chain drives: cheaper and easier to repair

How well did you know this?

Not at all

Perfectly

Straight spur gears description

noisy in ops.
used mainly for slow speeds to avoid excessive vibration (hand/powered winches)
speed ratio not to exceed 10:1

How well did you know this?

Not at all

Perfectly

helical spur gears description

teeth cut obliquely across gear width
angular contact creates side thrust (Fa) and is absorbed by bearings

quieter at high speeds and more durable
speed ratio not to exceed 10:1

How well did you know this?

Not at all

Perfectly

double helical gears description

teeth angles are opposite
thrust produced by each gear is counterbalanced
best for quiet, high speed, low thrust applications where heavy loads are applied
(large turbine, generators)

How well did you know this?

Not at all

Perfectly

rack and pinion description

converts straight-line motion to rotary motion and vice versa
for slow-speed reciprocating ops. (drilling machines)

How well did you know this?

Not at all

Perfectly

plain bevel gears description

turning of gears to an angle (turn corner)
for slow-speed applications without high impact force
speed ratio not to exceed 4:1

How well did you know this?

Not at all

Perfectly

spiral bevel gears description

teeth cut obliquely on the angular faces
for high speed & strength applications (drive axles / industrial machines)
durable

How well did you know this?

Not at all

Perfectly

worn and wheel description

worm is a screw
wheel has curved teeth for greater contact area
for high speed reduction in small space (steering mechanism, small power hand tools)
power supplied to the worm which drives the wheel
speed ratio not to exceed 70:1

How well did you know this?

Not at all

Perfectly

Hypoid gear description

like spiral bevel gear but pinion is offset from centre of the ring gear

How well did you know this?

Not at all

Perfectly

skew gears description

low load carrying capacity (due to small tooth contact area)
can be back driven
wide variety of speed ratios without change in centre distance of gear sizes

How well did you know this?

Not at all

Perfectly

pressure angles and their description

5deg: quiet but weak in bending
20deg: strong and quiet (in the middle of both)
25deg: very strong in bending but noisy

How well did you know this?

Not at all

Perfectly

diametral pitch meaning

tooth size for imperial gear (inches)
number of teeth in the gear for each inch of pitch diameter
DP = no. of teeth / pitch dia

How well did you know this?

Not at all

Perfectly

module of gear meaning

tooth size fore metric gear (mm)
module = PCD/no. of teeth (mm)

module = 25.4/DP

How well did you know this?

Not at all

Perfectly

addendum (ha) meaning and formula

height of tooth above pitch circle

ha = module

How well did you know this?

Not at all

Perfectly

dedendum (hf) meaning and formula

height of tooth below pitch circle

hf = 1.25 * module

How well did you know this?

Not at all

Perfectly

clearance meaning and formula

difference between addendum and dedendum
prevent tooth from bottoming out during ops.
clearance = hf - ha

working depth meaning and formula

max depth that the tooth extends into the space of mating gear

working depth = ha + hf - clearance = 2ha

PCD formula

m*T

m - module of gear
T - number of teeth

circular pitch formula

pi * (PCD/T)

T - number of teeth

whole depth formula

hf + ha

tooth thickness formula

CP / 2

CP - circular pitch

outside diameter (OD) formula

PCD + 2ha

root diameter formula

PCD - 2hf

gear speed formula (using angular velocity)

v = w1 * r1 = w2 * r2

w1 / w2 = r2 / r1

v = speed of gears

w = angular velocity of gears

r = PCR of gears

speed ratio of gears formula & speed and tooth relation

SR = input speed / output speed Na / Nd = Td / Ta

what is compound gear train and its advantages & applications

at least 1 intermediate shaft has 2 gears on the same axis large speed ratio can be obtained machine gear boxes, clock and watch mechanism

angular speed of gears and teeth relation in compound gear train

For pair A & B: Na / Nb = Tb / Ta For pair B & C: Nb / Nc = 1 For pair C & D: Nc / Nd = Td / Tc Final formula: Na / Nd = (Tb * Td) / (Ta * Tc) Na / Nd = (product of teeth on follower) / (product of teeth on driver)

worm gear special property

one way direction worm can turn wheel easily but not the other way round

difference in right and left hand worm gear

right-hand wheel when turning worm CW: rotate CCW when turning CCW: rotate CW left-hand wheel when turning worm CW: rotate CW when turning CCW: rotate CCW

planetary gear train purpose

reduce speed of aircraft engine's output shaft to a more acceptable speed for the propeller

advantages of planetary gear train

output and input shafts are inline drive occupies a smaller space (reducing aerodynamic drag) can produce different speed ratios

difference between involute and cycloid gears

involute: driving force by line contact (easier & cheaper to manufacture) compound marking should be a line along the tooth cycloid: total area contact (more power) compound marking is full area contact

what does the pattern of contact check of gears show

accuracy of gear teeth alignment of shafts end float

how is gear backlash affected by

gear wear thermal growth of gear change in centre distance

why is backlash necessary

prevent gear binding space for lubricant abnormal wear thermal expansion & contraction

what can cause excessive backlash

worn gear teeth excessive play in gear shaft, bearings or bushes worn keys and keyways incorrect fitting

end float/axial movement of gears causes

uneven wear on gear teeth | chafing of component casing

what does concentric check do

check if flank of tooth at PCD is parallel to shaft axis if not uneven wear will occur

gear inspections issues to check

contact check backlash & wear end float concentricity check corrective & corrosion pitting (initial bedding causes pits & cause by corrosion) discolouration (blueing in contact area due to overheating) end loading (not align causing increased wear) fretting (relative movement between gears, removes surface particles leading to corrosion) frosting (breakdown of lubricant) ridging & rippling (excessive loading/poor lubrication, plastic deformation formed) scratching & scoring spalling (fatigue failure results in surface of teeth breaking away) cracks