What its purpose? To provide speed n torque multiplication but the driver dont have and can't select a desired torque/ speed ratio like manual
What's in there? 8 major parts: Input shaft; output shaft; bands n multiplates clutches; planetary gear sets; oil pump; valve body; Servo n piston; torque converter.
While planetary gear set provides different gear/torque ratio; bands n clutches provide clamping 4 gear change, also absord torsion due to sudden torque n locks up.
The oil pump supplies oil to the valve body, lubing all component while the valve body is the automated hydraulic control center for changing gears n different speed/load conditions.
Torque converter replaces the clutch n the flywheel, the central magic of automatic transmission. it has mainly an Impeller, stator n overrunnning clutch, and a turbine, the turbine is the output, fluid is stuck between there. In operation of the torque converter, the main pricipal of moving fluid is cnetrifugal force. The impeller is connected to the engine crankshaft, when engine turns, impeller turns, creating rotational motion, then converts to kinetic motion towards the turbine. The flow hits the turbine vanes got converted into rotational again and kinetically got flown back to the stator, back to the impeller. So it is the centrifugal force that turns the turbine n the stator.
One more notable part is the governor located on the output shaft jut out side the transmission housing, When the output shaft turns faster, centrifugal force open a plunger letting more fluid inside to help increase high oil pressure @ high engine speed.
Thursday, June 16, 2011
Manual Transmisson
What is a manual transmission? There is a shift level, a gear box with 3 selector folks, an Interlock mechanism, 5 different gear ratio, engine provide a constant amount of horsepower with a range of speed 0-7000,8000 etc... rpm, and a manual clutch system.
now let say the engine is running @ 4000 rpm, 1st gear selected, clock says 33 kph; 2nd says 57 kph; 3rd say 77kph, but then acceleration @ 1st from 0-33 kph is just 2 secs; while @ 2nd 0-57 kph in 5-6 secs, and 3rd gear takes like 9-10 secs just to get up to 4000 rpm.( fictional theoretically relevant in game figures)
What does that tells you when the formula relating Torque/ RPM/ HP say: "HP = Torque x RPM ÷5252" (source: http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm). So basically the engine can only provide a limited maximum HP; then Torque and RPM is directly disproportional to each other. Gears allow the driver to select the right torque and speed ratio desired for suitably adapt different speed and load condition. Why in first gear @ same rpm the top speed is low but acceleration is quick, because @ 1st a high gear reduction ratio(3.7:1) between the driven and the driver multiplies the torque transfer up to for example 3.7 times, while it takes the driver 3.7 revs just to make 1 rev output. As we change into higher gear, our speed desire must be over the load desire, therefore a 3.33:1 multiply speed while reducing torque: its only take the driver 3.33 turns to make 1 rev output.
Notable gear: 1st; 2nd; 3rd: gear reduction. In these gear, speed ratio is reduced compare to direct output speed, crowning torque multiplications. Drive is transferred from input, to driver, then driven gear to output to final drive.
4th: direct drive ratio, drive from input straigh through output.
5th: Overdrive ratio actually for speed multiplication n the reduction of torque, therefore its ratio is 0.86:1=> driver drive less than 1 turn to complete 1 output=> speed improved.
How is drive transferred? What exactly happen?
The magic of the manual is the gear synchronizer assemply, 4 example between 1st n 2nd driven; 3rd n 4th driver, or 5th gear; there are synchro hubs that consist of a cone gear, baulk ring and the sliding hub, what it does is allowing the next gear to be selected smoothly by synchronizing gear teeth to alignment in order to engage the selected gear ratio with the output shaft.
When the next geat is selected, from the driver's shift knob to the shift folk that exert a force on the sliding hub. This pushes the baulk ring to engage in friction against the cone gear(the selected gear) , these 2 start the movement until both's dog teeth are aligned and matched with the grooves inside the sliding hub, then the gear is locked with the engaged shaft.
Reverse is a lil bit special it needs an additional gear to counter the drive direction, this gear is an idler, because of this, it is cost effective n quite reliable to use spur gears cuz they are simple and cheap.
When selecting gears, it is possible that 2 gears r selected @ the same time, this is no good, an interlock mechanism with its detent ball is used for this reason. it restricts to only 1 gear to be selected at a time, becasue there are 3 shift shafts, and when a gear selected the detent ball n spring locks the shaft 1 place, also pushes the other balls into locking grooves on other shaft, locking them from moving.
now let say the engine is running @ 4000 rpm, 1st gear selected, clock says 33 kph; 2nd says 57 kph; 3rd say 77kph, but then acceleration @ 1st from 0-33 kph is just 2 secs; while @ 2nd 0-57 kph in 5-6 secs, and 3rd gear takes like 9-10 secs just to get up to 4000 rpm.( fictional theoretically relevant in game figures)
What does that tells you when the formula relating Torque/ RPM/ HP say: "HP = Torque x RPM ÷5252" (source: http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm). So basically the engine can only provide a limited maximum HP; then Torque and RPM is directly disproportional to each other. Gears allow the driver to select the right torque and speed ratio desired for suitably adapt different speed and load condition. Why in first gear @ same rpm the top speed is low but acceleration is quick, because @ 1st a high gear reduction ratio(3.7:1) between the driven and the driver multiplies the torque transfer up to for example 3.7 times, while it takes the driver 3.7 revs just to make 1 rev output. As we change into higher gear, our speed desire must be over the load desire, therefore a 3.33:1 multiply speed while reducing torque: its only take the driver 3.33 turns to make 1 rev output.
Notable gear: 1st; 2nd; 3rd: gear reduction. In these gear, speed ratio is reduced compare to direct output speed, crowning torque multiplications. Drive is transferred from input, to driver, then driven gear to output to final drive.
4th: direct drive ratio, drive from input straigh through output.
5th: Overdrive ratio actually for speed multiplication n the reduction of torque, therefore its ratio is 0.86:1=> driver drive less than 1 turn to complete 1 output=> speed improved.
How is drive transferred? What exactly happen?
The magic of the manual is the gear synchronizer assemply, 4 example between 1st n 2nd driven; 3rd n 4th driver, or 5th gear; there are synchro hubs that consist of a cone gear, baulk ring and the sliding hub, what it does is allowing the next gear to be selected smoothly by synchronizing gear teeth to alignment in order to engage the selected gear ratio with the output shaft.
When the next geat is selected, from the driver's shift knob to the shift folk that exert a force on the sliding hub. This pushes the baulk ring to engage in friction against the cone gear(the selected gear) , these 2 start the movement until both's dog teeth are aligned and matched with the grooves inside the sliding hub, then the gear is locked with the engaged shaft.
Reverse is a lil bit special it needs an additional gear to counter the drive direction, this gear is an idler, because of this, it is cost effective n quite reliable to use spur gears cuz they are simple and cheap.
When selecting gears, it is possible that 2 gears r selected @ the same time, this is no good, an interlock mechanism with its detent ball is used for this reason. it restricts to only 1 gear to be selected at a time, becasue there are 3 shift shafts, and when a gear selected the detent ball n spring locks the shaft 1 place, also pushes the other balls into locking grooves on other shaft, locking them from moving.
The CLUTCH!!!
Clutch systems BASIC STUFF from classes.
Purpose : engage or disengage the power from engine to transmission as and when necessary
Most application: CLamping a friction disc in between two rotating metal dics
Name: Single dics/plate dry clutch
Friction disc is held against a heavy spring load.
Mainly 2 types:
Clutch plates: Diameter=torque capacity but increased pressure spring.
Pressure plate assembly
Sheet metal cover: smth that supports everything
Diapham spring(applies pressure)
Pressure plate
Spigot bearing supports the input shaft 4 the gearbox in the flywheel-can be a bronze bush or bearings(bull bearings or needle rollers)
There must be a freeplay between release bearing and the diaphragm spring
WHy Diaphragm spring is chosen to be in the clutch?
Low maintenace
Low weight, low engine powerloss
less effort to operate
Cost effective
Smoother operation
Can be used in a large range of vehicle.
Why I did What I did in practical?
We were given a mounted transmission + engine block and the clutch is just in between the flywheel and the input shaft of the transmission, so we unbolt them. Again, match marking is very important because on the clutch assembly there are spots that hold more load than other parts, hence their bolts slots are different not on a rounded symmetrical pattern.
I quickly notice the relation between theory notes and real clutch system, this one is nt a hydraulic adjustable control type where there is a slave chamber for fluid distribution, and when readjusting you depress the clutch you feel 1st level resistance n 2 nd resistance etc etc.... BUT NO, this is a spring/ mechanical type where your adjust the spring to set the freeplay on the clutch.
Why there must be a little freeplay? Opposite to most moving part, this thing feel relatively opposite. If on gears, freeplay is for heat expanding ability of teeth when operating preventing friction n binding then freeplay preset in clutch pedal is to set pre-load on the release bearing( note that this is a ball bearing pressed righ onto the center of the diaphragm spring to create pivot points hence disengage the clutch friction disc from the flywheel). If there is no freeplay that u can feel when u press the clutch, the friction disc might as well be set originally away or "just in contact" with the flywheel, hence there is not enough stop-friction between the clutch n the engine then the engine is not engaged with the transmission as when needed. The further result can be a burning friction disc that destroy it due to sliding friction between friction disc and flywheel.
So as we disconnect the spring, clutch controller wire first we need to set the freeplay after examining inside the clutch.
Apart on all the spring n screw and pivots, the most notable part is the friction disc, the front line of the clutch, it does the very painful job of SNAP!!! from zero movement to immediate engagement with the engine, and the engine doesn't do any mercy on the clutch, once it is clamped it takes whatever speed the engine is at. So at minimum idle about 900-1000, or even 5000-6000 rpm when u boys want to do a little sudden torque to burnout, the friction disc takes them all. I wonder with that much torsion, how it is going to last. Very well, it has 4 set of torsional spring to absorb all the torsion, effectively at every degree/angle/slice of the disc.
Nothing much to say about the clutch really its a standard dry plate diaphragm clutch we just check its condition and everything, make sure we find heat marks for damage for poor engagement n stuffs.
Overall, clutches have so many function but its main principal is to engage, disengage rotation parts. They are also effectively used to construct the LSD, mainly for create friction and transfer torque from wheel to wheel. Also in 4WD clutch disc are used in the viscous coupling, also doing the same job but with viscous fluid. In automatic transmission, there is no clutch in control but in construction, clutch packs and fluid are always used for unseen engagements.
The most exciting thing about clutches is: it is a must have for any drift car. With the clutch, it is so easy to bring the car's rev back to top in no time so your drift is still maintain, the RW are still burning, help the drifter no need to rely on too much engine power or handbrake. Hand brake is not really mobile to employ and require good practice, a second or more with the "angle generator" (E-brake) would probably spin out ruining the drift, probly only very tight corner using it or losing out on angle. But alternative is increasing the power but when your drift is at end and the power gets weak because too much road/ tyre friction, a press on the clutch will bring the rpm back on top like a re-engagement.
MIRACULOUS!!!!
Purpose : engage or disengage the power from engine to transmission as and when necessary
Most application: CLamping a friction disc in between two rotating metal dics
Name: Single dics/plate dry clutch
Friction disc is held against a heavy spring load.
Mainly 2 types:
Clutch plates: Diameter=torque capacity but increased pressure spring.
Pressure plate assembly
Sheet metal cover: smth that supports everything
Diapham spring(applies pressure)
Pressure plate
Spigot bearing supports the input shaft 4 the gearbox in the flywheel-can be a bronze bush or bearings(bull bearings or needle rollers)
There must be a freeplay between release bearing and the diaphragm spring
WHy Diaphragm spring is chosen to be in the clutch?
Low maintenace
Low weight, low engine powerloss
less effort to operate
Cost effective
Smoother operation
Can be used in a large range of vehicle.
Why I did What I did in practical?
We were given a mounted transmission + engine block and the clutch is just in between the flywheel and the input shaft of the transmission, so we unbolt them. Again, match marking is very important because on the clutch assembly there are spots that hold more load than other parts, hence their bolts slots are different not on a rounded symmetrical pattern.
I quickly notice the relation between theory notes and real clutch system, this one is nt a hydraulic adjustable control type where there is a slave chamber for fluid distribution, and when readjusting you depress the clutch you feel 1st level resistance n 2 nd resistance etc etc.... BUT NO, this is a spring/ mechanical type where your adjust the spring to set the freeplay on the clutch.
Why there must be a little freeplay? Opposite to most moving part, this thing feel relatively opposite. If on gears, freeplay is for heat expanding ability of teeth when operating preventing friction n binding then freeplay preset in clutch pedal is to set pre-load on the release bearing( note that this is a ball bearing pressed righ onto the center of the diaphragm spring to create pivot points hence disengage the clutch friction disc from the flywheel). If there is no freeplay that u can feel when u press the clutch, the friction disc might as well be set originally away or "just in contact" with the flywheel, hence there is not enough stop-friction between the clutch n the engine then the engine is not engaged with the transmission as when needed. The further result can be a burning friction disc that destroy it due to sliding friction between friction disc and flywheel.
So as we disconnect the spring, clutch controller wire first we need to set the freeplay after examining inside the clutch.
Apart on all the spring n screw and pivots, the most notable part is the friction disc, the front line of the clutch, it does the very painful job of SNAP!!! from zero movement to immediate engagement with the engine, and the engine doesn't do any mercy on the clutch, once it is clamped it takes whatever speed the engine is at. So at minimum idle about 900-1000, or even 5000-6000 rpm when u boys want to do a little sudden torque to burnout, the friction disc takes them all. I wonder with that much torsion, how it is going to last. Very well, it has 4 set of torsional spring to absorb all the torsion, effectively at every degree/angle/slice of the disc.
Nothing much to say about the clutch really its a standard dry plate diaphragm clutch we just check its condition and everything, make sure we find heat marks for damage for poor engagement n stuffs.
Overall, clutches have so many function but its main principal is to engage, disengage rotation parts. They are also effectively used to construct the LSD, mainly for create friction and transfer torque from wheel to wheel. Also in 4WD clutch disc are used in the viscous coupling, also doing the same job but with viscous fluid. In automatic transmission, there is no clutch in control but in construction, clutch packs and fluid are always used for unseen engagements.
The most exciting thing about clutches is: it is a must have for any drift car. With the clutch, it is so easy to bring the car's rev back to top in no time so your drift is still maintain, the RW are still burning, help the drifter no need to rely on too much engine power or handbrake. Hand brake is not really mobile to employ and require good practice, a second or more with the "angle generator" (E-brake) would probably spin out ruining the drift, probly only very tight corner using it or losing out on angle. But alternative is increasing the power but when your drift is at end and the power gets weak because too much road/ tyre friction, a press on the clutch will bring the rpm back on top like a re-engagement.
MIRACULOUS!!!!
Wednesday, June 15, 2011
Practical lesson with Differential
Yep! I did take the whole diff out, and these are the points that's worth noticing NOT what I did to pull things out but WHY I did those significant stuffs.
Based on what I've comprehended, I looked at it and its the Hypoid final drive helical gears both crown n pinion. I know because position of the pinion its just below the center line of the crown wheel. Then, I HAVE to identify ALL the match marking available, this is crucial for reassembly as well as performing task like checking the the meshing pattern using grease paint to determine the correct load, position, cleareance/ backlash between the pinion and the crown wheel. I MUST notice that a correct meshing and backlash n clearance result in smooth, quiet operation without overtime wear of the components teeth due to loads press on literally wrong location.
There are gears that need to be taken care about all those stuffs: Pinion, crown wheel, side gears, spider gears...and anything that moves like thrusts, bearings, casing
Cleaning and inspecting is a MUST-DO, the condition of the gears, bearings, thrust, collapsible spacer tell us how long these going to last or need replacig right away, these moving parts are sources or noise when operating.
The bearing type used to set the preload on the pinion is the taper-roller needle bearing, associates with a collapsible spacer.
Lubrication is a BIG reason of corrosion and noise, during inspection of the casing of the side gears n spider gears this is what I literally reported:
- The spider gears beds, both were heavily worn out. It shows lots of rust marks n heat marks, result of lack if lubrication and excessive preload n heat. This can be sanded and preload need to be reset.
SO this means that there is lack of lube=> lube every internal moving part, do it correctly enough. About the preload, i guess it was probly the side gears' cage-like screw there are 2 ovem 4 each side gear that when i reassemble them i just screw them into their own threads, and the crown wheel is moved from side to side due to this preload setter. So i figured this is backlash/ clearance of the crown as well as the side gears.
-I check the thrusts of the spider gears and one of them heavily worn out into an oval shape hole nt a round hole which fit the cross bar shaft, also there is an excessive line of damage due to over load n heat=> it must be replaced. So I found the fault, rectify the reason, find the source of the problem n fix it. Afterall, resetting the preload is required.
When re-assembling, we were required to set the pinion preload using the load tester its like a bar with torque ranges and a weight on it. I then came to understand the purpose of the collapsible spacer is to press into the bearing setting pre-load when the adjusting bolt is tightened.
In the end, not only reading but actually working with the diff opens my mind literally/ visually about what can go wrong inside a diff and how to make it right.
Based on what I've comprehended, I looked at it and its the Hypoid final drive helical gears both crown n pinion. I know because position of the pinion its just below the center line of the crown wheel. Then, I HAVE to identify ALL the match marking available, this is crucial for reassembly as well as performing task like checking the the meshing pattern using grease paint to determine the correct load, position, cleareance/ backlash between the pinion and the crown wheel. I MUST notice that a correct meshing and backlash n clearance result in smooth, quiet operation without overtime wear of the components teeth due to loads press on literally wrong location.
There are gears that need to be taken care about all those stuffs: Pinion, crown wheel, side gears, spider gears...and anything that moves like thrusts, bearings, casing
Cleaning and inspecting is a MUST-DO, the condition of the gears, bearings, thrust, collapsible spacer tell us how long these going to last or need replacig right away, these moving parts are sources or noise when operating.
The bearing type used to set the preload on the pinion is the taper-roller needle bearing, associates with a collapsible spacer.
Lubrication is a BIG reason of corrosion and noise, during inspection of the casing of the side gears n spider gears this is what I literally reported:
- The spider gears beds, both were heavily worn out. It shows lots of rust marks n heat marks, result of lack if lubrication and excessive preload n heat. This can be sanded and preload need to be reset.
SO this means that there is lack of lube=> lube every internal moving part, do it correctly enough. About the preload, i guess it was probly the side gears' cage-like screw there are 2 ovem 4 each side gear that when i reassemble them i just screw them into their own threads, and the crown wheel is moved from side to side due to this preload setter. So i figured this is backlash/ clearance of the crown as well as the side gears.
-I check the thrusts of the spider gears and one of them heavily worn out into an oval shape hole nt a round hole which fit the cross bar shaft, also there is an excessive line of damage due to over load n heat=> it must be replaced. So I found the fault, rectify the reason, find the source of the problem n fix it. Afterall, resetting the preload is required.
When re-assembling, we were required to set the pinion preload using the load tester its like a bar with torque ranges and a weight on it. I then came to understand the purpose of the collapsible spacer is to press into the bearing setting pre-load when the adjusting bolt is tightened.
In the end, not only reading but actually working with the diff opens my mind literally/ visually about what can go wrong inside a diff and how to make it right.
Final drive and Differential part 2
Differential
Differential is what i find most miraculous(jokes!) on the drive line side of the vehicle. I've just watched this hilarious video by Chevy it was sooo old presenting like the 1st generation of the diff. I then came to realize that was how they have come to invent the differential. Many years ago, wheel axle is just a bar connecting 2 wheels, but when it comes to a drive axle where 2 wheels are drivers and ability to comprehend steering, different load/terrain/ road conditions is needed, there comes the differential.
I've realized there are mainly 2 elements revolving this area: speed( rotational/ rpm) and torque.
1. Speed different:
When a car is steering left, the left wheel always travels less than the right wheel. And in order to keep equal, it has to turn faster. At the same time, both wheels are driven by the pinion/ crown wheel (final drive) set. This is the part that is miraculous about the DIFF. Examining the basic logical construction of the diff leads us right to the explanation or speed matter. Let assume that each wheel side is independent. In the diff hub there is a side gear for each wheel drive and both not locked with each other.This looks like they are gonna be able to be speed different freely, but how are they driven? So there is the final drive gear locked to one wheel. What about the other wheel how is it gonna get driven? If yes how are both of them gonna be free from each other? The answer is: there is a set of spider gears just idling freely in side the DIFF housing. They are put in mesh with the side gears but 90 deg cross-layout with them and have a shaft that keeps them idling in place. By this way, when there is a speed difference, they just be like: side gears are travelling at opposite direction so one spider spin a way one spin another way according to the difference between the side gears speeds.
Before all those miracles happen, the crown wheel which drives everything, are bolted to a cage that contains all the magical gears. Side gears are nt driven by locked in with the walls of the cage but spider gears are locked by a shaft to the cage, and the cage is the crown wheel so when the crown wheel spins, the locked spiders gear move with the housing pushing the side gears with them making them spin. This is when the car goes straight, both wheels are a@ equal speed.
This ability is so useful as it allows no tyre skidding during steering of any WD type, because every wheel is able to stick to the road on their own will.
For 4WD vehicle, there needs to be a DIFF @ front and one @ rear. But there's only 1 transmission out put then there needs to be a 3rd DIFF synchronising 2 UJs together. As far as i know this 3rd one needs to be able to switch on n off on different road condition. The reason 4 this is: when driven on plain road, steering n wheel sizes makes them turn @ different speed eventually, a 4WD without the 3rd DIFF is NO good for tar-sealed road or any concrete road because its a highly gripping road, allows no type skidding so if there is difference between front bridge n rear bridge eventually one of them is gonna get twisted. "Part-time four-wheel-drive systems don't have a differential between the front and rear wheels; instead, they are locked together so that the front and rear wheels have to turn at the same average speed. This is why these vehicles are hard to turn on concrete when the four-wheel-drive system is engaged"( how stuffs work source: http://auto.howstuffworks.com/differential1.htm)=> this makes a lot of sense.
However, on muddy, or rough terrain, cars need 2 be able to over run this so, all DIFF operation is locked so every wheel gets a chance of driving the car out of trouble. Plus there are rooms for skidding, some free " on air" time.
For any who concerns, here how the speed different works: OF course what's coming out of the final drive is constant, say...500 rpm. The car is turning left, so left wheel is turning at 375 rpm, guess how fast the right one turns....500+(500-375)=500+125=625. Now take R+L and average them: 625+375=1000; 1000/2=500= original final drive speed. Simple math huh?
2. Torque and traction
Take the maths exercise above as an example. When there is rpm obviously there is torque. Torque difference or speed difference i meant the same thing, but they might be differently illustrated. You see how torque is delivered equally 2 both wheel when going a straight line R-F-L is 500-500-500 and when turning left 625-500-375. So clearly torque delivered to left wheel decreases that torque delivered to right wheel gains the exact same amount: 125 rpm.
That was just the case with plain mechanical DIFF where both wheels get the same amount of road grip. In the case of Diff lock-up, when turning, inner wheel will spin while outer wheel will drag possessing the result of balanced amount of torque forced to both wheel=> this is the preferable case of drifting where it is encouraged to lose rear wheel traction to over-steer, skid, or power sliding etc...
What happen if there is one wheel on air while the other is turning? This is also a case of open differential operating. The wheel on air have no grip whatsoever all the torque will logically be transferred to the ground wheel, and the ar still move as usual? NO!!! The theory behind the open differential is "the open differential always applies the same torque to both wheels, and the maximum amount of torque is limited to the greatest amount that will not make the wheels slip"
(http://auto.howstuffworks.com/differential3.htm) This explains everything isn't it?
-When on dry cond there is plenty of grip, torque will only be limited by engine power, but in low grip cond, the torque provided by engine power can excess the threshold of road friction in this case is low therefore "burnouts"( when 2 wheels are locked 2gether).
-When one wheel is on good grip n the other is on thin ice, an open DIFF suffers because the wheel on ice won't get a torque that can excess the threshold of the very low friction allowed for maximum gripped acceleration, and so does the well-gripped wheel. In the end, the car won't move as much
-4WD; SUV with open diffs front n rear will also suffer on off-road, because when a wheel comes off the surface (which happens quite often) or lifts up at an amount enough to lose effectively all grip with the ground, the car might get stuck. Why? because when on air, very easy little torque will spin the wheel helplessly on the air while it is not enough to move the well on the load, so your car gets stuck.
3. Limited slip diff or positraction:
Soo with the recognized weaknesses of the open diff we can all guess out obviously what features the more advanced stuffs need to have. The problem was due to the limited grip on 1 wheel the other wheel doesn't get enough torque right? So we need more torque to the non-slipping wheel( on-load wheel) when those stinky situations happen. But how do they do that?
I'd say to gas more and make both wheels spin stronger, i might b able to move my car but then I waste gas inefficiently and my car ends up slipping. However, the solution is still making the load wheel spin with more torque when the slipping wheel is turning faster, it is exactly what these LSD are designed to achieve.
Most common LSD probably the clutch-type LSD, where there's a spring pack that pressed against the side gear to the clutch pack( actually friction disc). When the car moves straight, the clutches has no effect. But when steering, the outer wheel tries to spin faster hence resisted by the clutch pak get pressed with the outer side gear, wanting both wheels to travel at same speed, meanwhile adding more torque to the slower wheel. I think this also makes turning more effective because less slipping means more traction in turning. This special ability helps cars getting out of very stinky situations when one wheel is slipping it will try to over power the stiffness of the spring n the clutches friction to spin faster, hence the torque that is lost due to the resistance will be transferred to the slower( some case idle/ on load) wheel. In the end your car still be able to move out of the trouble but nt as much as engine power, but hey thats basically what we need.
An also popular LSD is the viscous coupling usually used between front n rear of a 4WD. It has 2 clutch paks one of the front one of the rear and stuck between all there is the thick fluid, all trapped in a box. when front drive tries to spin faster than rear drive due to steering, the front coupling will spin faster, driving the fluid with centrifugal force that also drives the rear clutch pak faster to catch up, resulting in more torque to the slower wheel. This principle is effectively giving more torque to the wheel on load as well as eliminate unnecessary spinning giving more traction steering and terrain over coming. I also see this can be popularly applied to 2 wheels drive as well.
""(Torsen( Torque- Sensing) is a torque sensitive LSD, works as an open differential when the amount of torque going to each wheel is equal. As soon as one wheel starts to lose traction, the difference in torque causes the gears in the Torsen differential to bind together. The design of the gears in the differential determines the torque bias ratio. For instance, if a particular Torsen differential is designed with a 5:1 bias ratio, it is capable of applying up to five times more torque to the wheel that has good traction. These devices are often used in high-performance all-wheel-drive vehicles. Like the viscous coupling, they are often used to transfer power between the front and rear wheels. In this application, the Torsen is superior to the viscous coupling because it transfers torque to the stable wheels before the actual slipping occurs.
The locking differential is useful for serious off-road vehicles. This type of differential has the same parts as an open differential, but adds an electric, pneumatic or hydraulic mechanism to lock the two output pinions together.
This mechanism is usually activated manually by switch, and when activated, both wheels will spin at the same speed. If one wheel ends up off the ground, the other wheel won't know or care. Both wheels will continue to spin at the same speed as if nothing had changed.)""http://auto.howstuffworks.com/differential6.htm) THIS MAKE HELLA LOT OF SENSE!!!
Final drive and Differential part 1
Final Drive
Final drive is the last section of the gear train and forms part of the drive line of the motor vehicle (Moodle). It often consist of a pinion gear driving a big ring gear( or crown wheel) and the final drive ratio is calculated by ring gear teeth divide by pinion gear teeth. Its main purpose is to slit up drive into 2 paths to each wheel drive. This mechanism is done by a pinion gear set longitudinally to the engine layout but perpendicularly to the crown wheel creating a 90 deg drive transmit.Final drive literally mean final gear drive ratio works just like gears drive in the gear box, for example: normally pinion/crown 3.8:1; 4.11:1 will give you higher engine revs, faster acceleration, more pulling power, less gas mileage and slower top speed. 3.73:1 will give you slightly lower engine revs, slower acceleration, less stump pulling power, slightly better gas mileage and a higher theoretical top speed.
Final drive "gears down" the engine speed, allowing the direct gear drive (4th) to be available in the gear box( very important).
From here, I've learned that there are different types of final drive set up:
a. Worm drive: basically is a screw with transverse thread along its body mesh with the crown wheel teeth. By this cause the pinion can only be placed somewhere above or below the crown wheel. I can see its only advantage is to prevent reward movement caused when car is @ slope. Otherwise this is not very ideal because it doesn't have deep mechanical contact, n slow as well therefore no good for heavy duty vehicle nor performance cars. Fortunately this is only the design of the past to modern vehicles.
b. Spiral Bevel gear: Helical teeth, pinion placed at middle height of the crown wheel, solving the worm's problem of drive shaft's height. Also, helical teeth allows it to operate smoother and more quiet, also better contact and drive efficiency.
From the spiral bevel, HYpoid gear set is the next generation, with helical teeth both crown n pinion but a lower set up from the centre line of the crown wheel. The number of contacting teeth is actually higher, allowing better contact, meshing leading to a higher strengths load and a higher gear reduction ratio. => Overall better drive efficiency. This is why hypoid gear final drive is most common application for modern vehicle.
"For practical purposes, it is often impossible to replace low efficiency hypoid gears with more efficient spiral bevel gears in automotive use because the spiral bevel gear would need a much larger diameter to transmit the same torque. Increasing the size of the drive axle gear would require an increase of the size of the gear housing and a reduction in the ground clearance"( Source: wikipedia: http://en.wikipedia.org/wiki/Spiral_bevel_gear#Comparison_of_spiral_bevel_gears_to_hypoid_gears). This is the reason why hypoid gear possesses more strength than the spiral because it can deliver more torque with the number of contacting teeth it has.
And that's all I seem to be able to put on about final drive right now.
Tuesday, June 14, 2011
19/05/2011 the cv joint
I just realized the modern general JOINTS layout for all type of wheel drives: all cars need Tripods CVJ. For FWD, tripod is used on the inner side of the haft shaft, to provide axle movement for suspension distorsion. As for RWD, both sides of half shaft are similar because the outer CVJ does not need steering ability, in which 6 balls (Zeppa or Birdfield) CVJ is used. RWD and 4WD need additional UJs set to lengthen the drive transfer to the distant wheel drives from the transmission.
CV shorts for Constant velocity, it means as the drive angle changes, the drive speed delivered is still preserved. As for universal joint, the drive delivered from driving shaft through the trunnion to the driven shaft is not constant( universal joint post ;link;) so this needs another universal joint to cancel out this difference, so in the end drive is responsively 100% transferred to the pinion gear/ final drive. The universal joint design is ideal for RWD vehicle because of this, not for FWD, totally unnecessary and not logical.
Why CV joint? FWD or RWD, they need a short, homo-kinetically transferable at variously wide amount of drive angle; simply because from output transmission-final drive- half shafts to drive wheels is short, therefore high angle drive occurs. The design of CVJ just overwhelms the UJs. First of all is the Tripod CVJ. This CVJ is needed for any half shaft because they are the last link of drive transfer from transmission to THE wheel drive. Due to various load conditions put on the suspension, the joint has to be able to operate successfully compensating changes in angle, distance from wheel drive axle to the differential/ final drive. This is why tripods joint is very important. The design consists of 3-balls or 3-spherical rollers (set 120 degree apart) around the interconnecting shaft and a sliding hub( outer race) providing end travel(plunger type): the key for the tripod to CONSUME angles and length variations.
In FWD, it is crucial that the outboard of the half shaft is fixed type. This to me simply mean it is the 6-balls Zeppa or Birdfield( watever) type. 6 balls rollers trapped between the cage and the inner race, smoothly sliding in their outer race grooves, plus the inner race has splines connected to the interconnecting shaft, providing very high and direct angle drive transfer, allowing for steering ability of a FWD. The balls movement is sequential and coordinated, like when a ball move outwards, the opposite ball is dug deep inside the outer race, this makes the whole balls set fixed inside the outer race.
Dismantling these is easy as we got instruction. But the real thing that makes your money is looking at parts that have the tendency to be damaged.
1- Tripods: Its really easy to unclip the boot cover to get into the rollers housing ad then just slide them out. Before that, remember to remove the seal. So what do I look for? Moving parts always get damaged by the way they operate, they have never been perfect. What gets damaged more when doing burnouts, tyres or the tripods rollers? I'd rather check the rollers for right-on cracks, damages...and the needle bearing inside them. Then I check the whole inter shaft for torsion as assumed that excessive load applied. Outer race and splines grooves are also important to check out for cracks, frays, corrsion etc...This is because, if any of these gets worn out, firstly noticeable is the noise it makes when driving, then drive is not efficiently transmitted, eventually cause high fuel consumption, poor performance. And most dangerously, the sliding plunge joint gets bind up, or the shaft gets 2 much torsion would probly break on point.
The rubber boot cover is important as well as it keeps all the lubes inside the rollers joint housing, keeping it smooth. Always keep an eyes for any cracks, leaks on the rubber boot especially the retainer and collar strap make sure they are tight. Because when a leak of lube happens, clearly your joint lose out on lube that it heats stronger/ faster while operating, hence corrosion happens faster. Also, leaks allow all sort of dirt deposit into the joint, corroding, binding it from smooth operation.
2- 6 balls: The difference between the Tripod and the Birdfield is that the 6-balls has a retain circlip plus its design that allow no end movement. This circlip is often noted as to take the balls housing out of the outer race. Without the circlip, the inner race and ball cage can move freely as to the point where the balls can be removed out of the cage one by one. Special puller/ press tool is required if the outer housing refuse to move. But in my experience, i just need to be as precise as choosing the right corner then use a soft face hammer n a press to press 1 side of the housing down. There is usually a more opened cage hole than the other 5s that is the right one to level. Once the 1 ball is taken out the rest should be easy.
Again, I check for cracks on the balls, damage on the outer race, cage, inner race splines etc, make sure the rubber boot is tight, nt leaking, n everything regreased. The reason i did those is the same as why i have to check the tripods...
When all done, I check for all smooth operation of them joints.
CV shorts for Constant velocity, it means as the drive angle changes, the drive speed delivered is still preserved. As for universal joint, the drive delivered from driving shaft through the trunnion to the driven shaft is not constant( universal joint post ;link;) so this needs another universal joint to cancel out this difference, so in the end drive is responsively 100% transferred to the pinion gear/ final drive. The universal joint design is ideal for RWD vehicle because of this, not for FWD, totally unnecessary and not logical.
Why CV joint? FWD or RWD, they need a short, homo-kinetically transferable at variously wide amount of drive angle; simply because from output transmission-final drive- half shafts to drive wheels is short, therefore high angle drive occurs. The design of CVJ just overwhelms the UJs. First of all is the Tripod CVJ. This CVJ is needed for any half shaft because they are the last link of drive transfer from transmission to THE wheel drive. Due to various load conditions put on the suspension, the joint has to be able to operate successfully compensating changes in angle, distance from wheel drive axle to the differential/ final drive. This is why tripods joint is very important. The design consists of 3-balls or 3-spherical rollers (set 120 degree apart) around the interconnecting shaft and a sliding hub( outer race) providing end travel(plunger type): the key for the tripod to CONSUME angles and length variations.
In FWD, it is crucial that the outboard of the half shaft is fixed type. This to me simply mean it is the 6-balls Zeppa or Birdfield( watever) type. 6 balls rollers trapped between the cage and the inner race, smoothly sliding in their outer race grooves, plus the inner race has splines connected to the interconnecting shaft, providing very high and direct angle drive transfer, allowing for steering ability of a FWD. The balls movement is sequential and coordinated, like when a ball move outwards, the opposite ball is dug deep inside the outer race, this makes the whole balls set fixed inside the outer race.
Dismantling these is easy as we got instruction. But the real thing that makes your money is looking at parts that have the tendency to be damaged.
1- Tripods: Its really easy to unclip the boot cover to get into the rollers housing ad then just slide them out. Before that, remember to remove the seal. So what do I look for? Moving parts always get damaged by the way they operate, they have never been perfect. What gets damaged more when doing burnouts, tyres or the tripods rollers? I'd rather check the rollers for right-on cracks, damages...and the needle bearing inside them. Then I check the whole inter shaft for torsion as assumed that excessive load applied. Outer race and splines grooves are also important to check out for cracks, frays, corrsion etc...This is because, if any of these gets worn out, firstly noticeable is the noise it makes when driving, then drive is not efficiently transmitted, eventually cause high fuel consumption, poor performance. And most dangerously, the sliding plunge joint gets bind up, or the shaft gets 2 much torsion would probly break on point.
The rubber boot cover is important as well as it keeps all the lubes inside the rollers joint housing, keeping it smooth. Always keep an eyes for any cracks, leaks on the rubber boot especially the retainer and collar strap make sure they are tight. Because when a leak of lube happens, clearly your joint lose out on lube that it heats stronger/ faster while operating, hence corrosion happens faster. Also, leaks allow all sort of dirt deposit into the joint, corroding, binding it from smooth operation.
2- 6 balls: The difference between the Tripod and the Birdfield is that the 6-balls has a retain circlip plus its design that allow no end movement. This circlip is often noted as to take the balls housing out of the outer race. Without the circlip, the inner race and ball cage can move freely as to the point where the balls can be removed out of the cage one by one. Special puller/ press tool is required if the outer housing refuse to move. But in my experience, i just need to be as precise as choosing the right corner then use a soft face hammer n a press to press 1 side of the housing down. There is usually a more opened cage hole than the other 5s that is the right one to level. Once the 1 ball is taken out the rest should be easy.
Again, I check for cracks on the balls, damage on the outer race, cage, inner race splines etc, make sure the rubber boot is tight, nt leaking, n everything regreased. The reason i did those is the same as why i have to check the tripods...
When all done, I check for all smooth operation of them joints.
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