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Premium member Presentation Transcript AUTOMATIC TRANSMISSIONS: AUTOMATIC TRANSMISSIONS Algonquin College Automotive Programs GD Howarth, Prof. Sep 2001AUTOMATIC TRANSMISSION : AUTOMATIC TRANSMISSION Torque Converter Hydraulic Control Unit Planetary Gear UnitTORQUE 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 converterTORQUE CONVERTOR – CONSTRUCTION: TORQUE CONVERTOR – CONSTRUCTIONTORQUE CONVERTOR – OPERATION: TORQUE CONVERTOR – OPERATIONSTATOR 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 phaseONE WAY CLUTCH: ONE WAY CLUTCHSPEED RATIO: SPEED RATIO Speed ratio is the comparison of pump and impeller speeds expressed as a percent. Speed ratio = pump speed turbine speed X 100TORQUE MULTIPLICATION: TORQUE MULTIPLICATION Torque multiplication occurs at speed ratios lower than 90% Torque multiplication is highest when the torque converter is at STALLSTALL SPEED: STALL SPEED The torque converter is at stall when: The turbine is stationary The pump is turning at maximum RPMCOUPLING POINT: COUPLING POINT The coupling point occurs at a speed ratio of approximately 90% Torque multiplication is no longer providedVORTEX 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 vanesLOCK – 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 slippingPLANETARY 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 UnitGEAR 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 teethGEAR 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 gearDIRECT 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 gearsOVERDRIVE: 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 gearPLANETARY GEAR SETS: PLANETARY GEAR SETS Planetary gear sets are used to provide: Park & Neutral Gear reduction Direct drive Overdrive ReversePLANETARY GEARS: PLANETARY GEARSPLANETARY 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 ReactionJOB 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 movingPARK / NEUTRAL: PARK / NEUTRAL Park and neutral can be achieved by: Disconnecting the input member Disconnecting the reaction memberGEAR 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 reductionGEAR 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 reductionDIRECT 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 occursREVERSE: REVERSE Reverse will only occur if the carrier is held The sun gear drives The ring gear is drivenREVERSE OVERDRIVE : REVERSE OVERDRIVE If the ring gear was to drive the sun gear while holding the carrier, reverse would occur in an overdrive ratioSIMPSON 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 sizeRAVIGNEAU GEAR SETS: RAVIGNEAU GEAR SETS Ravigneau gear sets use: Two sun gears (different sizes) Two sets of pinion gears One ring gearRAVIGNEAU GEAR SETS: RAVIGNEAU GEAR SETSACTUATORS: ACTUATORS Actuators are used to connect members of the planetary gear set to the: Input shaft Output shaft Transmission caseACTUATOR TYPES: ACTUATOR TYPES The actuators used in automatic transmissions can be: Driving devices Brake devicesDRIVE DEVICES: DRIVE DEVICES Driving devices are multiple disc wet clutch packs Attach input shafts to planetary gear set membersCLUTCH PACKS: CLUTCH PACKSHOLDING 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 SpragCLUTCHES 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 caseBRAKE BANDS: BRAKE BANDS Band brakes use a servo piston to apply the band around the outside of a drumBRAKE BAND: BRAKE BANDBRAKE 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 CantileverDIRECT ACTING: DIRECT ACTINGLEVER LINKAGE: LEVER LINKAGECANTILEVER LINKAGE: CANTILEVER LINKAGEONE 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 casePowerPoint Presentation: http://www.youtube.com/v/xUzNE-PfaZw&feature=relatedHYDRAULIC 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 UnitPUMP TYPES: PUMP TYPES Transmission pumps may be: Gear and crescent Vane Variable displacement vaneGEAR: GEARVANE: VANEVARIABLE DISPLACEMENT: VARIABLE DISPLACEMENTVALVES: VALVES There are two main types of valves used in automatic transmissions: Pressure regulating or modulating valves Relay valvesPRESSURE 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 overpressureMAIN 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 pressureMAIN LINE REGULATION : MAIN LINE REGULATIONBOOST 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 LOADENGINE LOAD: ENGINE LOAD Engine load can be determined by either: Throttle Pressure Modulator PressureTHROTTLE 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 VALVEMODULATOR 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 pressureMODULATOR: MODULATORMODULATOR: MODULATORGOVERNOR PRESSURE: GOVERNOR PRESSURE Governor pressure is: Used as an indication or road speed Developed from main line pressure Controlled by the governor valveGOVERNOR VALVE TYPES: GOVERNOR VALVE TYPES The three main types of governor valves are: Spool valve Ball bearing Shaft mountedSPOOL GOVERNORS: SPOOL GOVERNORSBALL GOVERNORS: BALL GOVERNORSSHAFT MOUNT GOVERNORS: SHAFT MOUNT GOVERNORSSHIFT VALVES: SHIFT VALVES Shift valves route line pressure to the appropriate drive device when the hydraulic “decision” pressures cause them to moveSHIFT VALVES 1: SHIFT VALVES 1 THROTTLE PRESSURE GOVERNOR PRESSURESHIFT VALVES 2: SHIFT VALVES 2SHIFT VALVES 3: SHIFT VALVES 3ACCUMULATORS: ACCUMULATORS The purpose of accumulators is to cushion the shift feel to increase customer satisfactionACCUMULATOR TYPES: ACCUMULATOR TYPES Accumulators can be: Independent Integral Valve – type Restrictions (fixed orifices) can also be used to increase shift feelINDEPENDENT ACCUMULATORS: INDEPENDENT ACCUMULATORS Independent accumulators require a separate bore with hydraulic passageways Full pressure does not reach apply device until the accumulator is bottomedINTEGRAL 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 bandsVALVE TYPE ACCUMULATORS: VALVE TYPE ACCUMULATORSAlgonquin College Automotive Programs: Algonquin College Automotive Programs Dennis Howarth, Prof. Jan 2002 You do not have the permission to view this presentation. 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