Transmission Hydraulic Systems Chapter 4

Introduction How the transmission develops hydraulic pressure How transmission generates, regulates and modifies pressures Control of up shifts and downshifts Lubrication and cooling of transmission How apply devices are applied

Pump Types Three TypesThree Types –Gear Pump –Rotor Pump –Vane Pump Driven by Torque ConverterDriven by Torque Converter Page 56C

Gear Type Pump Continually operating whenever engine is running Two meshing gears Inner gear powered by torque converter Fluid is carried between gear teeth Positive Displacement Requires pressure regulation Page 56C

Rotor Pump Inner Drive Rotor Driven Outer rotors Operates and delivers fluid whenever the engine is operating Page 57C

Vane Pump Vanes are operated by centrifugal force Can be positive displacement or Variable displacement pump Are self regulating Variable Displacement –Moving Slide controlled by regulated pressure See Page 58C

Pressure Regulation Regulator ValveRegulator Valve –Variable Regulated Pressure Electronic RegulationElectronic Regulation –Uses solenoid to modify system pressure by pulse width modulation Building to Max Pressure Page 61C

Pressure Regulator Valve Bleeds off pressure when maximum pressure is reached. Exhausts back to sump If left unregulated can damage components Page 61C

Transmission Hydraulic Pressures Mainline Pressure Throttle Pressure Governor Pressure Page 59C

Mainline Pressure (“line pressure”) Regulated Mainline PressureRegulated Mainline Pressure Is source for all flowIs source for all flow Controlled by pressure regulatorControlled by pressure regulator Applies bands and clutchesApplies bands and clutches Feeds Valve Body valvesFeeds Valve Body valves Applies pressure to one end of pressure regulator valveApplies pressure to one end of pressure regulator valve Page 60C

BOOST PRESSURE Boosted Mainline PressureBoosted Mainline Pressure –Boost Valve to raise pressure at low rpm and high engine load Other pressures are used to modify regulated pressureOther pressures are used to modify regulated pressure Page 61C

Throttle Pressure (“modulated pressure”) Engine Load SensingEngine Load Sensing –Mechanical –Vacuum – Electronic Works against governor pressureWorks against governor pressure Primary Shift Control signalPrimary Shift Control signal Can be Electronic ControlledCan be Electronic Controlled Always less or equal to mainline pressureAlways less or equal to mainline pressure Page 62C

Mechanical Throttle Valve Operation Page 67C

Throttle Valve Operation Low Pressure

TV Valve Pressure Higher Pressure PAGE 68c

Vacuum Operated Throttle Valve (vacuum modulated) Page 68c

Governor Pressure Road Speed signalRoad Speed signal Opposes TV pressure to control shift pointsOpposes TV pressure to control shift points Driven by output shaftDriven by output shaft Higher speeds = Higher pressureHigher speeds = Higher pressure Electronic transmission use a PWM solenoidElectronic transmission use a PWM solenoid Governor TypesGovernor Types –Gear Driven Spool Valve TypeSpool Valve Type Check-ball TypeCheck-ball Type –Shaft Mounted Valves allow fluid to not bleed off the higher speed you go.Valves allow fluid to not bleed off the higher speed you go. Governors stick sometimes and can be cleanedGovernors stick sometimes and can be cleaned

Centrifugal Governor Operation Governor Types: Gear Driven, Shaft mounted and Electronic Solenoid Spool Valve operated Page 71c

Torque Converter Pressure Fluid couplingFluid coupling Fills torque converter during start upFills torque converter during start up Regulated by fill valveRegulated by fill valve Torque Converter Clutch Apply PressureTorque Converter Clutch Apply Pressure

Shifting and Shift Operations Manual ValveManual Valve Throttle ValveThrottle Valve Downshift ValvesDownshift Valves Governor ValveGovernor Valve –Spool Valve design –Check-ball design –Shaft Mounted governors Page 73c

Manual Valve Operation Positioned manually by gear selector lever Lever moves valve to one of several detent positions Directs mainline pressure to correct shift valves and apply devices Electronic transmission have a MLPS Page 66C

Shift Valve Operation Shift Valves are: –Flow directing –Switching valves Spool Type valves –Governor Pressure on one end –Throttle Pressure on other end with spring assist –Blocks or allows fluid flow –Valves must move instantly Page 73C

Shift Valve Operation When Vehicle speed low Throttle pressure and spring Pressure are higher than Governor pressure When speed is high, governor Pressure is higher than throttle Pressure. Allows mainline pressure to pass Through and cause a upshift Page 73c

Valve Body (The Brain)

Lubrication Flow and Pressure

Hydraulic Circuit Low Gear 1 – 2 Shift valve controls upshifts and downshifts between first and second gears 2 –3 shift valve controls upshifts and downshifts between second and third gears

Hydraulic Circuit Second Gear

Hydraulic Circuit Third Gear

Electronic Shift Control

ACCUMULATORS Serves as a “shock absorber” for the system Cushions application of servos and clutches –Allows a gradual application of apply device Independent Piston –Type Accumulator –Plumbed in parallel with servo Integral Piston _ Type Accumulator –Built into the servo assembly Valve Type Accumulator –Contains a small valve to restrict fluid flow Page 111C

ORIFICES Small restriction in a fluid passage Functions like a pressure regulating valve Delay pressure build up on one side Eventually equalizes on other opposite side FIG Page 75C

The End

Oil Cooler Flow and Pressure Fluid must be cooled Transmission must be cooled

Band and Clutch Apply Pressure