AUTOMATIC TRANSMISSIONS

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AUTOMATIC TRANSMISSIONS: 

AUTOMATIC TRANSMISSIONS Algonquin College Automotive Programs GD Howarth, Prof. Sep 2001

AUTOMATIC TRANSMISSION : 

AUTOMATIC TRANSMISSION Torque Converter Hydraulic Control Unit Planetary Gear Unit

TORQUE CONVERTER - PURPOSE: 

TORQUE CONVERTER - PURPOSE The purposes of the torque converter are to: Transmit engine torque into the transmission Multiply engine torque Dampen engine pulsations Provide “flywheel” mass Torque converter

TORQUE CONVERTOR – CONSTRUCTION: 

TORQUE CONVERTOR – CONSTRUCTION

TORQUE CONVERTOR – OPERATION: 

TORQUE CONVERTOR – OPERATION

STATOR OPERATION: 

STATOR OPERATION The purpose of the stator is to re-direct fluid flow to assist engine rotation during the multiplication phase The stator must not interfere with the fluid flow during the coupling phase

ONE WAY CLUTCH: 

ONE WAY CLUTCH

SPEED RATIO: 

SPEED RATIO Speed ratio is the comparison of pump and impeller speeds expressed as a percent. Speed ratio = pump speed  turbine speed X 100

TORQUE MULTIPLICATION: 

TORQUE MULTIPLICATION Torque multiplication occurs at speed ratios lower than 90% Torque multiplication is highest when the torque converter is at STALL

STALL SPEED: 

STALL SPEED The torque converter is at stall when: The turbine is stationary The pump is turning at maximum RPM

COUPLING POINT: 

COUPLING POINT The coupling point occurs at a speed ratio of approximately 90% Torque multiplication is no longer provided

VORTEX FLOW: 

VORTEX FLOW Vortex flow is a “spiraling” or rolling flow of fluid in a torque converter when the speed ratio is very low (during torque multiplication)

ROTARY FLOW: 

ROTARY FLOW Rotary flow occurs in a torque converter at high speed ratios – the fluid is simply carried along with the pump and turbine vanes

LOCK – UP TORQUE CONVERTERS: 

LOCK – UP TORQUE CONVERTERS In order to increase efficiency a hydraulically applied clutch locks the turbine to the pump case under certain conditions to remove slipping

PLANETARY GEARS - PURPOSE: 

PLANETARY GEARS - PURPOSE The planetary gear unit provides: A path for engine power to get to the drive shaft / final drive A way of changing torque, speed, and direction of the engine power Planetary Gear Unit

GEAR REQUIREMENTS: 

GEAR REQUIREMENTS Gear requirements for a motor vehicle include:

GEAR RATIO: 

GEAR RATIO Gear ratio is the comparison of input gear revolutions to achieve one output revolution Driven gear teeth / Drive gear teeth

GEAR REDUCTION: 

GEAR REDUCTION Gear reduction provides greater output torque at reduced output speed Gear reduction is achieved by having a small gear drive a large gear

DIRECT DRIVE: 

DIRECT DRIVE Direct drive is a gear ratio which results in transmission of input torque and speed to the output shaft without affecting the torque and speed Direct drive is achieved with two equally sized gears

OVERDRIVE: 

OVERDRIVE Overdrive is a gear ratio which provides reduced output torque at a greater output speed Overdrive is achieved by having a larger gear driving a smaller gear

PLANETARY GEAR SETS: 

PLANETARY GEAR SETS Planetary gear sets are used to provide: Park & Neutral Gear reduction Direct drive Overdrive Reverse

PLANETARY GEARS: 

PLANETARY GEARS

PLANETARY OPERATION: 

PLANETARY OPERATION In order for the planetary gear set to transmit power, each of the three members of the planetary gear set must be perform one of three jobs: Input Output Reaction

JOB DESCRIPTION: 

JOB DESCRIPTION INPUT: The input gear receives the engine power OUTPUT The output gear provides drive force to the drive shaft or final drive REACTION The reaction member must be HELD and prevented from moving

PARK / NEUTRAL: 

PARK / NEUTRAL Park and neutral can be achieved by: Disconnecting the input member Disconnecting the reaction member

GEAR REDUCTION - #1: 

GEAR REDUCTION - #1 In this case: The smallest gear drives The middle sized gear is held The largest gear (the carrier) is driven Result: Maximum gear reduction

GEAR REDUCTION - #2: 

GEAR REDUCTION - #2 In this case: The middle sized gear drives The smallest gear is held The largest gear is driven RESULT: Gear reduction

DIRECT DRIVE: 

DIRECT DRIVE If any two members are locked together (both providing input) direct drive occurs.

OVERDRIVE: 

OVERDRIVE When the carrier drives either other gear OVERDRIVE occurs

REVERSE: 

REVERSE Reverse will only occur if the carrier is held The sun gear drives The ring gear is driven

REVERSE OVERDRIVE : 

REVERSE OVERDRIVE If the ring gear was to drive the sun gear while holding the carrier, reverse would occur in an overdrive ratio

SIMPSON GEAR SETS: 

SIMPSON GEAR SETS Simpson gear sets use a common sun, two carriers, and two ring gears The sun, ring, and pinions are the same size

RAVIGNEAU GEAR SETS: 

RAVIGNEAU GEAR SETS Ravigneau gear sets use: Two sun gears (different sizes) Two sets of pinion gears One ring gear

RAVIGNEAU GEAR SETS: 

RAVIGNEAU GEAR SETS

ACTUATORS: 

ACTUATORS Actuators are used to connect members of the planetary gear set to the: Input shaft Output shaft Transmission case

ACTUATOR TYPES: 

ACTUATOR TYPES The actuators used in automatic transmissions can be: Driving devices Brake devices

DRIVE DEVICES: 

DRIVE DEVICES Driving devices are multiple disc wet clutch packs Attach input shafts to planetary gear set members

CLUTCH PACKS: 

CLUTCH PACKS

HOLDING DEVICES: 

HOLDING DEVICES Holding devices are used to control the reaction member of a planetary gear set Holding devices can be: Multiple disc wet clutches Brake bands One way clutches Roller Sprag

CLUTCHES AS BRAKES: 

CLUTCHES AS BRAKES Clutches used as brakes are identical in construction to clutches used as driving devices except the steels are splined to the transmission housing or case

BRAKE BANDS: 

BRAKE BANDS Band brakes use a servo piston to apply the band around the outside of a drum

BRAKE BAND: 

BRAKE BAND

BRAKE BAND TYPES: 

BRAKE BAND TYPES Brake bands may be: Single wrap Double wrap Double Wrap Single Wrap (light) Single Wrap (heavy)

LINKAGE: 

LINKAGE Servo linkages used include: Direct acting Lever Cantilever

DIRECT ACTING: 

DIRECT ACTING

LEVER LINKAGE: 

LEVER LINKAGE

CANTILEVER LINKAGE: 

CANTILEVER LINKAGE

ONE WAY CLUTCHES: 

ONE WAY CLUTCHES One way clutches have the inner race splined to the planetary member and the outer race splined or fastened to the transmission case

PowerPoint Presentation: 

http://www.youtube.com/v/xUzNE-PfaZw&feature=related

HYDRAULIC CONTROL UNIT: 

HYDRAULIC CONTROL UNIT The hydraulic control section of the transmission uses hydraulic pressures to control and perform shifting of the transmission gears Hydraulic Control Unit

PUMP TYPES: 

PUMP TYPES Transmission pumps may be: Gear and crescent Vane Variable displacement vane

GEAR: 

GEAR

VANE: 

VANE

VARIABLE DISPLACEMENT: 

VARIABLE DISPLACEMENT

VALVES: 

VALVES There are two main types of valves used in automatic transmissions: Pressure regulating or modulating valves Relay valves

PRESSURE REGULATION: 

PRESSURE REGULATION Pressure regulation is used to: Limit the oil pressure in the transmission Control shifting In addition to primary regulation, some transmissions use a “blow off” valve to prevent overpressure

MAIN LINE PRESSURE: 

MAIN LINE PRESSURE The first pressure developed in the transmission is called MAIN LINE PRESSURE It is controlled by the opening point of the pressure regulator valve All other transmission pressures are derived from main line pressure All hydraulic devices are operated on main line pressure

MAIN LINE REGULATION : 

MAIN LINE REGULATION

BOOST PRESSURE: 

BOOST PRESSURE Under certain circumstances, mainline pressure must be increased to increase the holding pressure of the hydraulic devices High torque Reverse Low gear High load Heavy throttle demand

“DECISION PRESSURE”: 

“DECISION PRESSURE” In order to “decide” what gear to be in the transmission must look at road speed and engine load – just like the driver of a manual transmission ROAD SPEED ENGINE LOAD

ENGINE LOAD: 

ENGINE LOAD Engine load can be determined by either: Throttle Pressure Modulator Pressure

THROTTLE PRESSURE: 

THROTTLE PRESSURE Throttle pressure is: A common means of indicating engine load and driver demands Derived from main line pressure Controlled by the throttle valve, which is directly linked to the throttle plate (engine intake)

THROTTLE VALVE: 

THROTTLE VALVE

MODULATOR PRESSURE: 

MODULATOR PRESSURE Modulator pressure is: A means of converting manifold pressure (indicating engine load) to hydraulic control pressure Modulator pressure is derived from main line pressure

MODULATOR: 

MODULATOR

MODULATOR: 

MODULATOR

GOVERNOR PRESSURE: 

GOVERNOR PRESSURE Governor pressure is: Used as an indication or road speed Developed from main line pressure Controlled by the governor valve

GOVERNOR VALVE TYPES: 

GOVERNOR VALVE TYPES The three main types of governor valves are: Spool valve Ball bearing Shaft mounted

SPOOL GOVERNORS: 

SPOOL GOVERNORS

BALL GOVERNORS: 

BALL GOVERNORS

SHAFT MOUNT GOVERNORS: 

SHAFT MOUNT GOVERNORS

SHIFT VALVES: 

SHIFT VALVES Shift valves route line pressure to the appropriate drive device when the hydraulic “decision” pressures cause them to move

SHIFT VALVES 1: 

SHIFT VALVES 1 THROTTLE PRESSURE GOVERNOR PRESSURE

SHIFT VALVES 2: 

SHIFT VALVES 2

SHIFT VALVES 3: 

SHIFT VALVES 3

ACCUMULATORS: 

ACCUMULATORS The purpose of accumulators is to cushion the shift feel to increase customer satisfaction

ACCUMULATOR TYPES: 

ACCUMULATOR TYPES Accumulators can be: Independent Integral Valve – type Restrictions (fixed orifices) can also be used to increase shift feel

INDEPENDENT ACCUMULATORS: 

INDEPENDENT ACCUMULATORS Independent accumulators require a separate bore with hydraulic passageways Full pressure does not reach apply device until the accumulator is bottomed

INTEGRAL ACCUMULATORS: 

INTEGRAL ACCUMULATORS Integral accumulators use the “non-working” side of a servo piston as an accumulator Uses existing bore and piston assembly Aids in “pull off” and “hold off” of bands

VALVE TYPE ACCUMULATORS: 

VALVE TYPE ACCUMULATORS

Algonquin College Automotive Programs: 

Algonquin College Automotive Programs Dennis Howarth, Prof. Jan 2002