190303C Flashcards
Powershift and Automatic Transmission Mechanical/Electronic Components
What are the two general categories of powershift and automatic transmission application?
cycling
hauling
how do these applications differ from each other?
by the arrangement of speeds and input/output direction that tranny offers
what are the two general categories of power shift and auto trannys based on design of internal gearing?
planetary type
countershaft type
what is the function of a transmission?
to modify engine power to propel heavy equipment through operating conditions it was designed for
what torque/speed relation would you need with heavy loads or a steep grade?
high torque, low speed
what torque/speed relation would you need with light loads or even ground?
low torque, higher speed
what is another function that transmissions provide?
power can be drawn off to drive components. (PTO)
What is the similarity between power shift and automatic transmissions?
they allow speed and direction change with no interruption to power flow from engine
How does a power shift tranny differ from an auto?
speed and direction changes are made at the discretion of the operator
all auto trannys are power shifts, but not all______ are autos
power shifts
how many reverse speeds are there on a power shift tranny?
as many as there are forward speeds
how does an auto tranny differ from a power shift?
spend changes are made independent of the operator action
how does an auto tranny make shifts?
receives info from ground speed and operator demand for power
what application uses power shift trannys?
cycling applications (repeated forward and reverse)
what units perform cycling applications?
loaders, dozers
what application uses auto trannys?
hauling applications
what does an auto tranny allow the operator to do?
focus their attention on maneuvering the machine
the gears used in planetary gear sets are in constant mesh, what does this prevent?
grinding and missed shifts when changing gears
a smaller, more compact planetary gear set is capable of transmitting the same amount of torque as a larger spur gear set because gear tooth loading is spread among all of the contact points in the gear set
T or F
True
why can smaller bearings and thrust washers be used on planetary gear sets?
axial and radial thrust loads are offset in a planetary set
planetary gear sets are extremely versatile in that they are capable of providing many _____ of speeds and directions particularly when multiple sets are used
combinations
Why are planetary gear sets used in heavy equipment power shift and auto shift trannys?
to modify torque and speed from engine
What gear style is usually seen on planetary gears?
straight cut spur or helical
what can the planetary carrier metal be made from?
cast iron, aluminum, steel
what do planetary gears commonly rotate on to reduce friction between gears and pinion shafts?
needle bearings
how is end thrust absorbed between gear ends and carrier?
on brass or steel thrust washers
what conditions can a simple planetary gear set create?
- reduction in fwd ranges
- reduction in reverse ranges
- direct drive
- neutral
- overdrive in fwd and reverse
what does gear ratio refer to?
of revolutions the input (drive) gear makes to complete one revolution of the output (driven) gear.
what are planetary pinions only used for?
transfer torque or change direction
what is gear reduction?
input speed is higher than output speed
what is overdrive?
torque reduced, speed increased
what is neutral/freewheeling?
power input but no power output
What are two speed reduction conditions?
first speed slow, second speed fast
what are two overdrive conditions?
first speed slow, second speed fast
what are two reverse speed conditions?
first speed reduction, second speed overdrive
When does first speed reduction occur?
when the sun gear drives the carrier. smallest turning biggest. ring held
when does second speed reduction occur?
when ring gear drives carrier. medium turning biggest. sun held
what is a constant fact in planetary overdrive?
carrier being input member is always an overdrive
what is a constant fact in planetary reduction?
carrier being the output member is always a speed reduction
when does a first speed overdrive occur?
when carrier drives ring gear. sun held. biggest driving medium. mild
when does second speed overdrive occur?
when carrier drives sun. biggest driving smallest. ring gear held
what is a constant fact in planetary reverse?
carrier being held is always a reverse condition
when does a first speed reverse occur?
sun drives ring gear. small driving medium. carrier held. reduction
when does second speed reverse occur?
ring gear drives sun. medium driving smallest. carrier held. overdrive
what are 2 ways to achieve neutral from a single planetary set?
- when there’s an input but no held member
- when there’s no input to gear set
what are 2 ways to achieve direct drive from a single planetary set?
- locking 2 members together
- driving 2 members at the same speed (rpm) in the same direction
all clutches are hyd applied, ______________
spring released
what do clutches hold together in a planetary tranny?
what do brakes hold together in a planetary tranny?
2 components together
a component to the housing
What is a quick way to remember what clutches/brakes are held for reverse?
first clutch, last brake
what is the definition of a differential planetary gear set?
has a simple planetary with three rotating members, for dual input single output
What happens to carrier speed when the sun and ring gear are turning the same direction?
carrier speed always in between both speeds.
when the sun and the ring gear rotate in same direction, are there more or less teeth?
less teeth per rotation
what does a rotating clutch do?
hold 2 components together, rotates with components
what does a stationary clutch do?
hold component to tranny housing. “brakes” internal gear
the output speed and torque of the differential planetary set with sun and internal gear inputs is determined by?
tooth speed of the sun and ring gear
what does tooth speed refer to?
number of teeth passing by a given point in a given period of time. measured in teeth per second.
if ring gear is rotated in opposite direction of sun gear, what does the carrier speed do?
decreases
if ring gear is rotated at an equal negative tooth count speed to the sun gear, what does the carrier do?
carrier speed goes to 0
rotating the ring gear in reverse to the sun at a higher speed causes the carrier to?
start to travel in reverse as well
a direct drive within a planetary set exists when?
2 rotational speeds are equal, not tooth speed.
if tooth speeds are equal in opposite directions, what is the carrier doing?
carrier is not moving
All transmission clutches are _____ released?
spring
where do tranny clutches get their oil from?
tranny charging pump
what are 2 types of clutch discs used?
clutch discs (friction discs)
clutch plates
what are clutch discs?
made from sintered bronze or composite, steel discs that have friction material bonded to them.
what do the grooves on friction discs serve as a purpose for?
when disc is disengaged, allows oil to lubricate the groove lines
when disc engaged, allows oil to escape from grooves
what is the purpose of clutch disc teeth?
spline to the compound to be held reactionary
what are clutch plates?
located between every pair of clutch discs. provide a reaction surface where the clutch discs can act
what are the tangs on the outside of the clutch plates for?
holding a component stationary ( to tranny housing)
what are teeth on the outside of the clutch plates for?
spline to a clutch drum to hold 2 components together
what is used to apply the clutch?
hyd actuated pistons
what type of seal is common on a clutch piston?
lip seal
what is the difference between manual and power shift trannys regarding the gears being held?
gears in power shift/auto are held to their countershafts with multiple disc oil applied clutches rather than mechanical clutches
do countershaft transmissions use stationary clutches?
no, only rotating
what are high-low countershaft units for?
providing various speed ratios, from deep reduction, direct drive, or overdrive.
where do the clutch plates and discs spline to in a high-low countershaft unit?
clutch plates spline to the drum
clutch discs spline to the hub on the output shaft
the planetary gear set component that meshes with the sun and internal gear is called the planet carrier
T or F
False
it is the pinions not the carrier
what condition is it when both internal and sun gear rotating forward at the same tooth speed?
reduction
what condition is it when internal gear rotates forward and sun gear rotates in reverse at same tooth speed as internal?
neutral
wha condition is it when internal gear is rotating in reverse at a much higher tooth speed than the sun gear is rotation forward?
reverse
what condition is it when the internal gear and sun gear are rotating forward at equal rpm?
direct drive
