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HET Third Year Powertrain SAIT > 190303D > Flashcards

190303D Flashcards

Powershift and Automatic Transmission Control and Shifting

1
Q

what is the simplest form of transmission shift systems?

A

powershift shift control systems

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2
Q

why do units with torque converters or torque dividers generally require fewer gear ranges than those with hyd clutches?

A

engine torque is multiplied through those units before its supplied to tranny

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3
Q

the hydraulic system to control shifting in a power shift can be divided into 3 circuits?

A
  1. clutch application
  2. torque converter charging circuit
  3. tranny lube circuit
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4
Q

out of the 3 hydraulic circuits, how is pressure compared?

A

clutch application gets more pressure, then torque converter and lastly lube circuit

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5
Q

how is oil sent to clutch application circuit?

A

from charging pump driven off the tranny

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6
Q

what does a shift selector valve do?

A

directs oil flow to proper clutch pistons, ensures other clutch pressure is released back to tank

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7
Q

what is the oil state considered in the clutch pistons when the clutch pressure regulator valve opens?

A

static oil. except for leakage oil for lubrication

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8
Q

where does the oil go after the clutch pressure regulator valve opens?

A

to the torque converter

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9
Q

what prevents damage to the torque converter by limiting pressure?

A

torque converter relief valve

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10
Q

what valve is a clutch pressure regulator valve like?

A

a sequence valve. keeps pressure in first circuit

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11
Q

where does the oil flow after the torque converter?

A

to the filter and cooler, before going back to tranny lube circuit.

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12
Q

how are all power shift and auto tranny gearing components lubricated?

A

pressure lubricated, as the components can’t be submerged in oil

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13
Q

what is max lubrication pressure controlled by?

A

lubrication relief valve

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14
Q

what must you do when towing machinery with power shift or auto trannys?

A

bc of pressure lubrication, if engine isnt turning there’s no pressure lube= extensive damage

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15
Q

how can you avoid tranny damage while towing?

A

elevate drive wheels
remove drive axles
remove driveline to prevent tranny rotation

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16
Q

how do you check tranny oil level?

A

with engine at low idle and oil at operating temp

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17
Q

what does oil level that’s too low cause?

A

aeration of the charging pump, resulting in tranny clutch slippage, torque converter cavitation, lack of tranny lube oil pressure

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18
Q

what does an oil level that’s too high cause?

A

tranny component to be submerged in oil= excessive friction and tranny overheating

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19
Q

although transmission oil has similar characteristics to hyd oil, they are specially formulated to provide?

A

max life of friction material on transmission discs

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20
Q

the oil pump on a power shift transmission is a 4 section external gear type pump. what are the 4 sections?

A
  1. transmission scavenging pump
  2. torque converter scavenging pump
  3. transmission charging pump
  4. steering clutch and brake lubrication pump
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21
Q

what is unique about the transmission charging pump and steering clutch and brake lubrication pump in terms of how the oil is supplied?

A

both of those pumps have oil going through a strainer first before the pump to prevent contamination

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22
Q

what does the priority valve do on a power shift transmission circuit?

A

pressure control, ensures oil pressure is available for steering clutch and brake function before transmission function

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23
Q

what does a speed selector spool do?

A

directs oil from tranny charging pump to speed clutches in planetary tranny

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24
Q

what does the modulation relief valve do?

A

controls max clutch application pressure

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25
Q

what does a load piston do?

A

controls rate of pressure rise in clutch pistons (clutch modulation) to prevent shift shock and excessive clutch slippage

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26
Q

what does a ratio valve do?

A

acts like a torque converter relief valve. limits max pressure inside torque converter when engine is started with cold oil

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27
Q

what does the pressure differential valve do?

A

maintain clutch application pressure to speed clutch. keep the pressure higher than direction clutch. prevents machine from moving

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28
Q

what does the direction selector spool do?

A

directs oil from charging pump to direction clutches

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29
Q

what does the torque converter outlet relief valve do?

A

limits max working pressure in torque converter

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30
Q

how does a transmission oil cooler work?

A

transfers heat energy by flowing coolant through tubes and allowing hot oil to pass around these tubes

31
Q

why is the auto transmission shift controls more efficient that power shift?

A

tranny auto shifts speed ranges at optimum time in machine operating cycle

32
Q

what do auto trannys shift in accordance to?

A

ground speed and operator demand for power

33
Q

how does the control system reference machine ground speed?

A

with a governor circuit

34
Q

what is a governor?

A

device that converts rotation speed of tranny output shaft to hyd pressure signal to control shifting

35
Q

what is spool movement balanced by on a governor?

A

centrifugal force from flyweights and force created by hydraulic pressure

36
Q

governor and modulator circuits are provided oil from?

A

clutch application circuit

37
Q

as ground speed of the machine is reduced, governor pressure _______

A

decreases

38
Q

an orifice in the line carrying governor pressure to the shift signal prevents downshifts from happening too rapidly if:

A

output shaft stops suddenly when brakes lock up

governor fails

39
Q

some auto trannys allow adjustment of tranny shift points. how is this done?

A

by adjusting shift signal valve spring force. reducing spring force= shifts occur earlier

40
Q

governor pressure is also used to apply and release the ______ in the torque converter?

A

lockup clutch

41
Q

what does the modulator circuit do?

A

alter shift points of tranny in relation to operator demand for power, indicated by throttle position.

42
Q

with a fully open throttle, will the modulator circuit shift?

A

no it will delay the shift

43
Q

delaying shifts with the modulator circuit can increase machine performance because it:

A

engine can develop greater hp in each speed range

greater machine momentum before upshifting

44
Q

why is it beneficial to keep the tranny in a particular speed range when going up a hill?

A

prevents vehicle from falling below the point of max torque production before downshifting

45
Q

how is modulator pressure in an auto tranny controlled?

A

with a modulator valve (regulates pressure in modulator circuit)

46
Q

how is the modulator valve operated with diesel engines?

A

by linkage or a cable attached to the throttle

47
Q

how is the modulator valve operated in a unit with a spark ignition engine?

A

operated by intake manifold pressure

48
Q

how does the modulator valve vary the pressure in the modulator circuit?

A

modulates proportional to position of engine throttle

49
Q

when throttle is wide open on the modulator valve, is the linkage exerting max or minimum force?

A

minimum force

50
Q

modulator pressure is regulated so that highest modulator pressure occurs during ____ throttle operation

A

closed

51
Q

lowest modulator pressure occurs at?

A

wide open throttle

52
Q

modulator pressure is used to assist _______ pressure to shift the shift signal valves?

A

governor

53
Q

when are transmission shift points delayed the most on a modulator circuit?

A

when throttle is in the wide open position

54
Q

why are transmission shift points delayed the most during wide open throttle?

A

because there is no modulator pressure to assist governor pressure to overcome shift signal spring force

55
Q

what are 4 types of shift dampening devices?

A
  1. orifice
  2. modulation
  3. trimmer
  4. accumulator
56
Q

if a clutch is released quicker than another clutch is engaged, the transmission will become out of gear. what will be the symptoms?

A

engine rpm flare and momentary freewheeling

57
Q

if a releasing clutch doesn’t full disengage before the applying clutch engages, what will be the symptom?

A

ending lugging and slowing of machine speed from internal binding

58
Q

an orifice controls clutch release rates by:

A

controlling return line oil from the piston cavity

59
Q

controlling the rate of clutch application is often called

A

modulation

60
Q

how does a trimmer valve work?

A

by using a valve assembly installed in parallel with the inlet line to the transmission clutch

61
Q

why would controlled clutch slippage under full throttle and heavy load conditions be undesirable?

A

it would promote rapid wear of clutch discs and eventually lead to clutch failure

62
Q

how can you eliminate clutch modulation at full throttle?

A

connect the spring cavity of the clutch modulation valve to modulator boost pressure

63
Q

why are electronic transmission shift controls more efficient and flexible than hydraulic shifting?

A

they can use a microcomputer built into the ecu to perform other functions

64
Q

what functions can the ecu perform in relation to shifting?

A
  1. interface with other vehicle control and monitoring systems
  2. provide diagnostic info
  3. monitor tranny pressure + temp
  4. prevent operator from shifting at a bad time
  5. control aux functions- neutral start, backup alarm
  6. allow customizing tranny operating parameters
65
Q

what are 3 categories electronic transmission shift control system components fall into?

A

input components
processing components
output components

66
Q

what are the input components?

A
  1. power supply
  2. shift selector
  3. speed sensor
    4.throttle position sensor
  4. pressure and temp sensors
  5. machine/engine communication link
67
Q

what does the transmission ecu do?

A
  1. control up and down shifting based on ground speed and throttle position
  2. control clutch modulation
  3. provide diagnostic info
  4. provide warning to operator when a tranny malfunction occurs
68
Q

What are the output components?

A

solenoids
transmission warning output devices
backup alarms

69
Q

what are shift solenoids responsible for?

A

transmission speed and direction changes, as well as the application and release of torque converter lockup clutches

70
Q

what is a vehicle interface module used for?

A

to connect ecu to vehicle electrical system

71
Q

the function of the clutch pressure regulator valve is to:

A

limit application pressure applied to transmission clutch pistons

72
Q

the hydraulic governor in an automatic transmission operates by balancing the centrifugal force of the governor flyweights against?

A

governor pressure

73
Q

what component of an electronic automatic shift control system performs the same function as the governor in hyd controlled systems?

A

a speed sensor

HET Third Year Powertrain SAIT (8 decks)

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