Car Transmission System

TRANSMISSION

OBJECTIVESOBJECTIVESTo understand the operational

principles and basic mechanisms of transmission system

Lecture – 1 hourWorkshop – 1 hour

TRANSMISSION SYSTEM (1)TRANSMISSION SYSTEM (1)

Manual gear knob

Manual gear box

Manual gear boxManual transmission system

5-speed manual gearbox

TRANSMISSION SYSTEM (2)TRANSMISSION SYSTEM (2) Green shaft (input shaft) & gear

turn at the same rpm as the engine

Red shaft (layshaft) & gears are directly connected to the input so it spins when input shaft spins

Yellow shaft (output shaft) is splined shaft connected directly to drive shaft through differential to drive wheels (If wheels are spinning output shaft spins)

If engine is off with car coasting output shaft turns inside blue gears (blue gears & layshaft are motionless)

Collar connects one of two blue gears to output shaft via dog teeth

TRANSMISSION SYSTEM (3)TRANSMISSION SYSTEM (3) Moving knob forward & backward

moves collar to engage the gears Reverse gear is handled by a

small idler gear (purple) Importance of transmission:–Engine redline (max. rpm

above which engine explodes)–Engines have narrow rpm

ranges (horsepower & torque are at their maximum)

Synchronizers allow collar & gear to make frictional contact before dog teeth make contact (collar & gear synchronize their speeds before teeth need to engage

TRANSMISSION SYSTEM (4)TRANSMISSION SYSTEM (4)A car engine spins all

the time & car wheels don't (to stop without killing the engine wheels, engine needs to be disconnected from the engine)

Flywheel connected to engine

Clutch plate connected to the transmission

Pressure plate

Clutch plate

Spring

Spring

TRANSMISSION SYSTEM (5)TRANSMISSION SYSTEM (5)Springs force on pressure plate Clutch plate springs - isolate

transmission from shock of clutch engaging

Friction material on the clutch disc wears out (similar to the friction material on the pads of a disc brake pads/shoes of a drum brake; clutch slips & lost of power)

Driver who slips the clutch a lot will wear out clutch a lot faster

Worn throw-out bearing (rumbling noise whenever the clutch engages)

TRANSMISSION SYSTEM (6)TRANSMISSION SYSTEM (6) Other clutches:–Automatic transmission with several

clutches used to engage and disengage various sets of planetary gears–Car air conditioning compressor with

magnetic clutch

–Engine-driven cooling fan with thermostatically controlled viscous clutch

TRANSMISSION SYSTEM (7)TRANSMISSION SYSTEM (7)Ideally, transmission should be

flexible in its ratios that engine runs at its single, best rpm value (continuously variable transmission - CVT) – Honda City

Manual transmission checklist:–Check for oil leaks (RM5000 new Kancil

gearbox) Manual transmission test drive–With transmission lever in neutral,

parking brake applied & engine idling, listen to any loud noises when clutch pedal pressed or released– Try to drive the car at all speeds one by

one - every speed should shift smooth & easily without any noises or jerks


Manual transmission test drive–While driving at 2nd or 3rd gear, try to

press down sharply on the accelerator pedal for an instance (clutch should not slip, any slipping i.e., engine rpm increases but speed remains the same clutch most likely has to be replaced)–Try to drive with acceleration &

deceleration (there should be no whining or humming noise under any condition with all gears should shift easily & noiselessly)


TRANSMISSION SYSTEM (10)TRANSMISSION SYSTEM (10)Automatic transmissions:–no clutch pedal–no gear shift

Automatic transmission (gearbox plus torque converter) – like manual gearbox & its clutch

Torqueconverter

Auto gearbox

Auto transmission system

TRANSMISSION SYSTEM (11)TRANSMISSION SYSTEM (11) In automatic transmission, same set of

gears produces all of the different gear ratios (planetary gearset)

Planetary gearset – A set of bands to lock parts of gearset – Three wet-plate clutches to lock other parts

of gearset – Hydraulic system controlling clutches &

bands – Large gear pump to move transmission fluid

around Planetary gearset has 3 main parts: – Sun gear – Planet gears & planet gears' carrier– Ring gear


TRANSMISSION SYSTEM (13)TRANSMISSION SYSTEM (13)Each of these 3 parts can be input,

output or stationary (determines gear ratio)

First Gear - 2.4:1Second Gear - 0.67:13rd gear - 1:1 ratio in 3rd gearOverdrive has a faster output speed than

input speed (output of engine goes straight to transmission)

Ratio = 1 / (1 + S/R) = 1 / ( 1 + 36/72) = 0.67:1 (an engine turning at 2000 rev/min output speed is 3000 RPM allowing cars to drive at freeway speed while the engine speed stays nice and slow

TRANSMISSION SYSTEM (14)TRANSMISSION SYSTEM (14) Differentials (where engine power, in most

cars, makes its last stop before spinning the wheels) –Aim engine power at the wheels –Act as final gear reduction in the car

(reduce rotational speed of transmission one final time before it hits the wheels) – Transmit power to the wheels while

allowing them to rotate at different speeds during turning

Device that splits engine torque two ways, allowing each output to spin at a different speed

Differential is found on all modern cars & trucks, and also in many all-wheel-drive (full-time 4WD vehicles)


Differential

TRANSMISSION SYSTEM (16)TRANSMISSION SYSTEM (16)Final drive ratio (gear ratio in the

differential)Open differential always applies the

same amount of torque to each wheelTwo factors determining how much

torque can be applied to the wheels:–equipment– traction

Dry conditions - torque applied to wheels limited by engine & gearing

TRANSMISSION SYSTEM (17)TRANSMISSION SYSTEM (17) In low traction - amount of torque limited

to greatest amount that will not cause a wheel to slip under those conditions (if you give the car more gas after the wheels start to slip, the wheels will just spin faster – problem with open differentials

Limited slip differential (LSD) – positraction - allows more torque to be transferred to the non-slipping wheel

TRANSMISSION SYSTEM (18)TRANSMISSION SYSTEM (18)Automatic transmission checklist–Place your car at a level surface, start

engine, set transmission lever to "P“ & let engine idle –Pull transmission dipstick–Wipe it off with a lint free clean

rag/tissue– Insert it back carefully all the way

down into its place–Pull again & check fluid level

TRANSMISSION SYSTEM (19)TRANSMISSION SYSTEM (19)Automatic transmission

checklist –Pull again & check fluid

levelEngine cold fluid within

"COLD" marksEngine hot fluid level at

upper end of "HOT" mark (top it up if it is lower)

Check fluid condition also: too black & a burnt smell -transmission may not last

TRANSMISSION SYSTEM (20)TRANSMISSION SYSTEM (20)Automatic transmission

checklist –Pull again & check fluid

levelThere should not be any

metal filings or black flakes

Topping up transmission fluid–Use only specified

transmission fluid (check your manual)

TRANSMISSION SYSTEM (21)TRANSMISSION SYSTEM (21)Topping up transmission

fluid–Add a small amount of

fluid through dipstick pipe as shown in the image & do not overfill it–Wait for a few minutes

to let fluid to flow down –Start engine & check

level again

TRANSMISSION SYSTEM (22)TRANSMISSION SYSTEM (22)Transmission maintenance–Most of transmission troubles start

after overheating Under heavy loadContinuous stop & go traffic in hot

weatherRacingAccelerating too hard to free the car At higher temperatures transmission fluid

burns loosing its lubricating qualities & becomes oxidized leaving deposits all over inside

Exposed to heat rubber seals & gaskets inside transmission become hardened causing leaks

TRANSMISSION SYSTEM (23)TRANSMISSION SYSTEM (23)Transmission maintenance–Most of transmission troubles start

after overheating Metal parts warp & loose their strength

–Poor design–After being rebuilt by inexperienced

technician–Harsh driving–Too low or too high transmission

fluid level–Wrong transmission fluid type

TRANSMISSION SYSTEM (24)TRANSMISSION SYSTEM (24)How to prevent the transmission from

damage–Always check your parking space for

leaks (get it fixed before it caused something serious) –Once in a while check transmission

fluid level & condition –Use only same type of the

transmission fluid as specified in owner's manual–Never shift to “R” or “P” until car

comes to a complete stop

TRANSMISSION SYSTEM (24)TRANSMISSION SYSTEM (24)How to prevent the transmission from

damage–Never shift from “P” mode when

engine rpm is higher than normal idle –Always hold a brake down when

shifting from “P”–Do not tow with drive wheels on the

road–Go to transmission shop when you

experience any problems with your transmission such as leaks, noises, problems with shifting, etc.

TRANSMISSION SYSTEM (25)TRANSMISSION SYSTEM (25)ATF (owner’s manual)Fluid change (40,000 km or so)Good conditions – clean & odorless Transmission screen/filter

THE ENDTHE ENDIQ + EQ + SQ = TQ*

Engineering

Car Transmission System