Modern Automotive

1
PowerPoint for
Modern Automotive Technology
by Russell Krick
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Chapter 57
Automatic Transmission Fundamentals
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Contents

• Basic automatic transmission
• Hydraulic system
• Parking pawl
• Automatic transmission power flow
• Electronic transmission control
• Continuously variable transmission
• Complete transmission assemblies

4
Automatic Transmission

• Performs the same functions as a manual
  transmission, but it shifts gears automatically
• Senses engine speed and load to determine shift
  points
• Uses internal oil pressure to shift gears
• Computers are often used to control shift points

5
Components
Basic Automatic Transmission

• torque converter
• input shaft
• oil pump
• valve body

• pistons and servos
• planetary gearsets
• bands and clutches
• output shaft

6
Simplified Automatic Transmission
7
Transmitting Power

• The torque converter uses fluid
• The bands and clutches use friction
• The gears vary output speed and torque

8
Transmission Housings and Case

• Bell housing
• surrounds the torque converter
• made of aluminum
• Transmission case
• encloses the clutches, bands, gearsets, and
  shafts
• made of aluminum

9
Transmission Housings and Case

• Oil pan
• stores the oil supply
• made of thin, stamped steel or cast aluminum
• Extension housing
• supports the output shaft
• a seal on the rear end prevents oil leakage
• made of aluminum

10
Transmission Housings and Case
11
Torque Converter

• A fluid clutch
• Provides a means of coupling and uncoupling the
  engine from the transmission

12
Torque Converter Principles

• Two fans demonstrate the action inside a torque
  converter

13
Torque Converter Construction

• A torque converter consists of four basic parts
• outer housing
• impeller or pump
• turbine
• stator

14
Torque Converter Construction
15
Torque Converter Construction

• Blades on the impeller and stator direct oil
  circulation onto the blades of the turbine

16
Torque Converter
17
Impeller

• Driven by the engine
• Integral part of the housing
• Produces oil movement within the converter

18
Turbine

• Driven by the impeller
• Splined to the transmission input shaft
• Fits in the front of the housing
• Oil is the only connection between the impeller
  and the turbine

19
Stator

• Improves oil circulation
• Increases efficiency and torque by directing the
  oil flow toward the turbine
• Helps make use of nearly all the force produced
  by the moving oil
• Located between the impeller and the turbine,
  mounted on a one-way clutch

20
Converter Housing
21
Flywheel Action

• The torque converter is very large and heavy
• The torque converter serves as a flywheel to
  smooth power pulses
• The flywheel on the engine is thin, stamped steel

22
Torque Converter Operation (Engine Idling)

• The impeller spins slowly
• A small amount of oil is thrown into the stator
  and turbine
• Not enough force is developed to spin the turbine
• The car remains stationary with the transmission
  in gear

23
Torque Converter Operation (Acceleration)

• The impeller spins faster
• More oil is thrown out of the impeller by
  centrifugal force
• The turbine begins to turn, moving the vehicle
  with some slippage
• At cruising speeds, the impeller and turbine spin
  at almost the same speed, with very little
  slippage

24
One-Way Clutch

• Allows the stator to turn in only one direction
• Stator action is only needed when the turbine and
  impeller turn at very different speeds
• the one-way clutch locks the stator
• When the turbine speed equals or exceeds the
  impeller speed, the stator can freewheel so it
  doesnt obstruct oil flow

25
Torque Multiplication

• Ability of a torque converter to increase engine
  torque applied to the transmission input shaft
• Occurs when the impeller is turning faster than
  the turbine
• acceleration
• As the turbine speed nears the impeller speed,
  torque multiplication drops off
• cruise

26
Stall Speed

• Occurs when the impeller is at maximum speed
  without rotation of the turbine
• Oil is thrown off the stator vanes at tremendous
  speeds
• The greatest torque multiplication occurs

27
Lockup Torque Converter

• Has an internal friction clutch mechanism that
  locks the impeller to the turbine, eliminating
  slippage
• Improves fuel economy
• Usually released in lower gears, allowing
  slippage and torque multiplication

28
Lockup Torque Converter

• The pressure plate can be used to lock the
  turbine to the converter housing, eliminating
  slippage

29
Lockup Converter Operation
Oil is transferred to the piston chamber
No oil pressure on the apply piston
Components
30
Input Shaft

• Connects the torque converter to the driving
  components in the transmission

31
Output Shaft

• Connects the driving components in the
  transmission with the drive shaft
• Runs on the same centerline as the input shaft

32
Stator Support

• A stationary shaft splined to the stator assembly
• A tube that extends forward from the front of the
  transmission
• Surrounds the input shaft

33
Planetary Gears

• A planetary gearset consists of the following
  components
• sun gear
• planet gears
• planet carrier
• ring gear
• The gears are always in mesh
• The gearset is strong and compact

34
Planetary Gearset
35
Planetary Gear Drive Conditions

• By holding or releasing the components, it is
  possible to
• reduce the output speed and increase the torque
• increase the output speed while lowering the
  torque
• reverse the output rotation
• provide direct drive
• freewheel (neutral)

36
Planetary Reduction

• Hold the sun gear (stop it)
• Drive the ring gear
• The planet carrier is the output member
• Gear reduction can also be produced by turning
  the sun gear and holding the ring gear

37
Planetary Reduction
38
Planetary Overdrive

• Drive the carrier
• Hold the ring gear
• The sun gear is the output member
• OR
• Drive the carrier
• Hold the sun gear
• The ring gear is the output member

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Planetary Overdrive
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Planetary Reverse

• Drive the sun gear
• Hold the carrier
• The ring gear is the output member

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Planetary Reverse
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Planetary Direct Drive

• The gearset acts as a solid unit
• Two members are driven
• The input and output members turn at the same
  speed

43
Planetary Direct Drive
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Planetary Neutral

• None of the members are held
• No power transfer occurs
• Used in neutral or park

45
Compound Gearset

• Combines two planetary units in one housing
• Provides more forward gear ratios than a simple
  planetary gearset
• A Simpson compound gearset uses a single sun gear
  to operate two sets of planet gears in one
  assembly

46
Compound Gearset
47
Clutches and Bands

• Friction devices that drive or lock planetary
  gearset members

48
Multiple Disc Clutches

• Several clutch discs are used to couple planetary
  gearset members
• Components
• drum
• hub
• apply piston
• spring(s)
• driving and driven discs
• pressure plate and snap ring

49
Clutch Construction

• The driving discs are splined to the hub
• The driven discs are locked in the drum

50
Clutch Operation
Released Applied
51
Driving Shell

• Commonly used to transfer power to one of the
  planetary sun gears

52
Driving Shell

• This drive shell connects the frontdrum to the
  sun gear

53
Bands

• Friction devices for holding members of the
  planetary gearsets
• Made of a steel strap with a lining of friction
  material on its inner surface
• Clamped around the clutch drum to stop drum
  rotation
• A band adjustment screw provides a means of
  adjusting the band-to-drum clearance

54
Band

• One end is anchored to the case

55
Servos

• Apply pistons that operate the bands
• A servo piston is a metal plunger that operates
  in the transmission case
• Rubber seals prevent oil leakage

56
Band and Servo Assembly
57
Band Operation

• When oil pressure enters the servo pressure
  chamber, the servo piston slides up in the
  cylinder, pushing on the end of the band
• Since the other end of the band is anchored, it
  tightens inward on the drum

58
Band Operation
59
Overrunning Clutches

• Used to hold a planetary gearset member
• One-way roller clutch that locks in one direction
  and freewheels in the other

60
Overrunning Clutches

• A. This action can stop movement of a planetary
  member
• B. The two races are free to turn independently

61
Hydraulic Valve Action

• The oil pump forces oil through the spool valve
  to the piston cylinder, pushing the piston
• When the spool valve switches position, pump
  pressure is vented
• The piston is forced back into its cylinder

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Hydraulic ValveAction
63
Hydraulic System

• System components work together to schedule
  shifting and operate the clutches and bands
  within the transmission
• The system also forces oil to high-friction
  points for lubrication

64
Hydraulic System
65
Transmission Oil

• Has several additives that make it compatible
  with the friction clutches and bands
• Various types are used

66
Oil Cooling

• Tremendous heat is developed inside an automatic
  transmission
• Torque converter slippage heats the oil
• Excess heat must be removed, or transmission
  failure could result

67
Oil Cooling

• The oil pump forces oil through lines to the
  cooler tank to provide cooling

68
Oil Pump

• Produces the pressure to operate the transmission
• Transmissions may have one or two pumps
• Often located behind the torque converter or in
  the valve body
• A sleeve or collar on the rear of the converter
  drives the pump

69
Oil Pumps
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Hydraulic Circuit
71
Pressure Regulator

• Limits the maximum amount of oil pressure
  developed by the oil pump
• A spring-loaded valve routes excess pump pressure
  out of the system

72
Manual Valve

• Operated by the shift mechanism
• When the gear shift lever is moved, the shift
  linkage moves the manual valve
• The valve routes oil pressure to the correct
  components

73
Vacuum Modulator Valve

• Senses engine load and determines when shifting
  to a higher gear should occur
• Manifold vacuum controls a diaphragm connected to
  the valve
• Phased out on electronic systems

74
Vacuum Modulator Valve

• Under high load, the valve delays upshifts

75
Governor Valve

• Senses vehicle speed to help control shifting
• The vacuum modulator and governor work together
  to determine shift points
• Consists of a drive gear, centrifugal weights,
  springs, a hydraulic valve, and a shaft

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Governor Valve
77
Governor Valve Operation

• When the output shaft speed is low, the weights
  are held in by governor springs
• The governor pressure is low, and the
  transmission remains in a low gear
• As shaft speed increases, the weights are thrown
  out farther
• The governor pressure increases, acting on the
  shift valve, and the transmission upshifts

78
Shift Valves

• Use control pressure (pressure from the
  regulator, governor valve, throttle valve, and
  manual valve) to operate the servos and clutches
• Schedule shifts based on engine load, road speed,
  and gear position

79
Kickdown Valve

• Causes the transmission to shift into a lower
  gear during fast acceleration
• A rod or cable links the throttle body to a lever
  on the transmission
• When the driver opens the throttle, the link
  moves the kickdown valve
• Hydraulic pressure overrides the normal shift
  control pressure, and the transmission downshifts

80
Valve Body

• Contains most of the hydraulic valves
• Bolts to the bottom or side of the case
• Housed in the transmission pan
• Passages in the valve body route oil from the
  pump to the valves and then into the case

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Valve Body
82
Parking Pawl

• Locks the transmission output shaft
• Keeps the car from rolling in park

83
Automatic Transmission Power Flow

• Powerflow varies depending on design and the
  number of forward gear ranges

84
Power Flow (3 Speed)

• Parts relating to power flow

85
Power Flow (3 Speed)
86
Power Flow (3 Speed)
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Power Flow (3 Speed)
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Power Flow (3 Speed)
89
Power Flow (3 Speed)
90
Overdrive Power Flow

• A transmission may have two input shafts
• turbine shaft
• direct input shaft

91
Power Flow (4 Speed O.D.)High Gear
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Electronic Transmission Control

• Uses sensors, actuators, and a computer to
  control shift points, torque converter lockup,
  downshifts, and other functions
• Provides more efficient operation

93
Transmission Control Module (TCM)

• Monitors and controls the functions of the
  transmission
• Shares data from the engine control module (ECM)
  such as engine load and speed
• Powertrain control module (PCM) monitors and
  controls the engine and transmission

94
TCM Operation

• Vehicle sensors feed data to the TCM
• The control module uses preprogrammed information
  to activate the shift solenoids and the torque
  converter lockup solenoid
• The solenoids open and close fluid passages to
  operate the transmission or transaxle

95
PCM Operation
96
Transmission Solenoids

• Solenoids are computer controlled

97
Solenoid Operation

• The TCM or PCM sends current through the solenoid
  windings
• The solenoid moves a control valve to alter
  hydraulic pressure and flow in the transmission
• TCMs and solenoids replace older mechanical and
  vacuum-operated devices, improving efficiency

98
Solenoid Operation

• A solenoid moves a spool valve

99
Solenoid Operation

• A solenoid controls pressure to a valve

100
Complete Computer System
101
Continuously Variable Transmission (CVT)

• Has an infinite number of drive ratios
• Uses two-piece centrifugal pulleys with variable
  diameters
• V-belts run between the pulley sets
• Provides excellent fuel efficiency by keeping the
  engine at its most efficient operating speed

102
CVT Operation

• Acceleration

Cruising Speeds
103
CVT Operation (Acceleration)

• The drive pulley has a small diameter
• The driven pulley has a larger diameter
• provides gear reduction for rapid acceleration

104
CVT Operation (Cruise)

• As speed increases, centrifugal force pushes the
  two-piece drive pulley together
• The belt rides out in the pulley, increasing the
  diameter
• a larger pulley drives a smaller pulley for more
  speed

105
Complete Transmission Assemblies
106
Four-Speed Transmission
107
Electronically Controlled Automatic Transmission
108
All-Wheel-Drive Transmission

• A transfer gear and shaft send the rear output
  shaft torque to the front differential