190303A Flashcards
Gearing Principles
On a gear tooth, what is the line dividing the tooth lengthwise?
pitch line
what is the upper portion of a gear tooth that’s been divided lengthwise?
face
what is the lower portion of a gear tooth that’s been divided lengthwise?
flank
when a gear tooth has a larger and narrower end, what is the smaller end called?
toe
when a gear tooth has a larger and narrower end, what is the larger end called?
heel
when describing wider gear sections, what is common regarding the heel and toe sections?
to separate them using a centre section
what is tooth profile?
the shape of the tooth
what is the root fillet on a gear tooth?
the lowest point between two teeth
why is the root fillet area slightly rounded?
gives gear tooth strength and reduce chances of cracking at that area
what is a drive side of a tooth?
convex side, the side that gears contact when being driven
what is the coast side of a tooth?
the concave side, the side that gears contact when the loaded vehicle is pushing the powertrain
what is path of power?
the power flow from engine flywheel to drive axles.
what can the path of power be used to determine?
which gears are actually in use and delivering power
what pitch circle diameter is the shortest?
the root diameter (root circle)
what pitch circle diameter is the greatest?
the outside diameter (outside circle)
where is the pitch diameter in relation to the face and flank?
on the centreline that divides the face and flank. (pitch circle)
where do teeth mesh at?
the pitch line
How do you find circular gear pitch?
find pitch circle, then find the exact centre of each gear tooth
what is gear pitch?
the distance between the gear tooth centrelines
why must the circular gear tooth pitch be the same on each gear?
provide great gear strength and max force can be delivered through the gears
What is clearance?
when gear teeth mesh, a small clearance exists between tip of one tooth and root between 2 teeth on the opposite gear
why is clearance needed?
help maintain a lubrication film
What is backlash?
clearance on the side of the gear tooth
why is backlash needed?
for expansion of gear teeth and lubrication
what should you be aware of when measuring or adjusting backlash?
changes in gear tooth profile as the gears wear during operation
how can you measure gear tooth backlash?
with a dial indicator
Why would you time a gear set?
to ensure they always operate in a specific relationship with one another. creates a specific wear pattern. gears have been lapped in their pattern and need to operate in that specific pattern
what is an example of a timed gear set from the book?
engine crank and cam
are gear teeth timed in an angle drive gear set?
yes
on an angle drive gear set, what is the smaller gear and larger gear called?
smaller: pinion
larger: crown
What are non-hunting gears?
gear set that develops a specific tooth contact wear pattern. will always contact the same tooth every revolution
do non-hunting gear sets need to be timed?
yes
How will the number of pinion teeth divide into the number of crown gear teeth on a non-hunting gear set?
equally, ex. 3:1, 5:1. ratio expressed as a whole number
What are partial non-hunting gears?
gear set that develops a unique wear pattern. will contact the same few teeth, but in 2-3 revolutions of the crown gear before the first pinion tooth returns to original point
do partial non-hunting gears need to be timed?
yes
how will the number of pinion teeth divide into the number of crown teeth on a partial non-hunting gear set?
of pinion teeth divides into crown teeth unequally, completes in one or 2 decimal places. ex: 4.45:1, 2.50:1
What are hunting gears?
no special wear pattern, every pinion tooth comes into mesh with every crown tooth at some point in operation
does a hunting gear set need to be timed?
no
how will the pinion teeth divide into the crown teeth on a hunting gear set?
pinion teeth divides into the crown teeth unequally, in a weird continuous number. ex: 3.333:1
what is direct drive?
when 2 gears in identical size are in mesh with one another. no speed/torque change. input= output
what ratio is direct drive?
1:1
How do you calculate gear ratio?
driven over drive
what is reduction?
when a smaller gear drives a bigger gear. output speed=1/2 input speed. low speed, high torque.
in gear ratios, how is a reduction usually seen?
reduction is always greater than 1. ex: 2:1, 3:1, 4:1
What is overdrive?
input gear is bigger than output gear. low torque, high speed. output speed= 2x input speed
where are overdrive gear sets often found?
in on highway vehicles to reduce input gear speed while keeping output gear speed
in gear ratios, how is overdrive usually seen?
less than 1. ex: 0.5:1, 0.25:1, 0.99:1
how can you change direction of rotation?
with an idler gear
is an idler gear involved in ratio calculations?
no, only input and output
what is one objective when adjusting gear mesh?
achieve a wear pattern that will provide maximum gear set service life
what conditions could two gears on two different parallel shafts but in mesh with each other operate?
direct drive, reduction, overdrive.
how could you create a reverse gear with 2 gears on 2 parallel shafts?
install a third shaft with an idler between the two gears
characteristics of straight cut spur gears?
most basic, tooth identical on all sides, cheap
where do straight cut gears contact?
across the entire pitch line
where are the main power transmission loads exerted on straight cut gears?
on the two meshing teeth at any one time
what is a benefit of using straight cut gears?
no axial thrust loadsw
what are disadvantages of straight cut gears?
not high strength, noisyw
where can straight cut gears be found?
in transmissions as main gears, or PTO’s
can internal gears mesh with other internal gears?
fuck no
what is needed to transmit power when using an internal gear?
an external gear in mesh
benefits of internal gears?
high load handling
what are single helical gears?
gears that are cut at an angle to the shaft
benefits of helical gears?
good strength and less noise.
what lengthens the time it takes for single helical gears to fully mesh?
the leading and trailing edges. ensures multiple teeth are involved in transmitting power
what is a disadvantage of single helical gears?
axial thrust loads. use thrust washers
what direction are axial thrust loads against a single helical gear?
both directions
where are single helical gears common?
transmissions or anywhere that you can control axial thrust loads
what are double helical gears?
single helical gears but two of them. separated by a line, line helps out with lubricating the gears
what is another name for double helical gears according to the book?
herringbone
benefits of double helical gears?
handles heavy torque loads, handle thrust loads like a breeze
why doesn’t the double helical gears have thrust loads?
the double design helps offset the axial thrust loads at opposite ends of the gears.
disadvantage of double helical gears?
expensive
What are rack and pinion gears?
change rotary motion to linear motion. mostly straight cut spur gears, the rack is like someone cut open a spur gear and laid it flat
what are angle drives?
used when needing to make a directional change, up to 90 degrees
what are straight cut bevel gears?
may use straight cut gear teeth. can be noisy and only for small load applications. changes direction of power
how can you gain strength in the design of angle drive sets?
use spiral gears
where does the pinion gear and shaft sit in relation with the crown gear on a spiral bevel gear set?
at the centreline of the crown gear
what does the short stub shaft on the pinion gear help with?
keeps pinion and crown in close contact during sudden high-torque shock loads
where does pinion sit in relation to centreline of crown gear on a hypoid angle gear set?
centreline of drive pinion and shaft is below centre of crown gear
benefit of hypoid angle gears?
good for high torque loads. has more tooth contact during meshing
why must you use special extreme pressure EP lubricant with hypoid gear sets?
these gear sets have a lot of sliding contact and pressure when meshing
Where doe the pinion sit in relation to the centre of the crown gear in an ambit gear set?
sits above the centreline. allows for higher driveline position (good for off-road clearance)
benefit of worm and wheel gear sets?
very strong, good for high torque loads. load will not overrun
where are planetary gear sets used?
where input and output shaft must operate on same plane
3 components of planetarium?
sun, ring, planets (on a carrier)
what is needed for a planetary to operate?
drive, driven, reactionary
if no member is held stationary on a planetary, what condition is it in?
neutral
if 2 members are held on a planetary, what condition is it in?
direct drive
if the carrier is held in a planetary, what condition is it in?
reverse
if the carrier is the driven component, what condition is it in?
reduction
if the carrier is driving, what condition is it in?
overdrive
