Wear Behavior of Wet Clutches
- Thread starter PandaBear
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MolaKule
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It's interesting he discusses drag torque right off.
Most people had never heard of this wrt to AT's until we discussed here:
Quote:
Hirev is on top of it. Good answer.
Anytime you have a spinning disk in fluid, the spinning disk imparts angular momentum to the fluid.
This angular momentum can be thought of as torque. This torque in turn imparts angular momentum to another clutch that may be spinning or turning at a different rpm.
There will be a drag torque induced in the fluid because of the differences in RPM between the rotating surfaces. This drag torque will raise the temperature of the ATF fluid and this Delta T has been measured.
This is similar to a torque converter in which there are differences in rpm between the driving and driven members of the TC.
http://www.bobistheoilguy.com/forums/ubb...Drag#Post530994
Most people had never heard of this wrt to AT's until we discussed here:
Quote:
Hirev is on top of it. Good answer.
Anytime you have a spinning disk in fluid, the spinning disk imparts angular momentum to the fluid.
This angular momentum can be thought of as torque. This torque in turn imparts angular momentum to another clutch that may be spinning or turning at a different rpm.
There will be a drag torque induced in the fluid because of the differences in RPM between the rotating surfaces. This drag torque will raise the temperature of the ATF fluid and this Delta T has been measured.
This is similar to a torque converter in which there are differences in rpm between the driving and driven members of the TC.
http://www.bobistheoilguy.com/forums/ubb...Drag#Post530994
What amaze me in that research paper is how clutch material wears are non linear and Torque specific. If the torque is low enough you can design a transmission that literally last 10 times longer, or long enough so that the clutch pack friction materials are not the limiting factor.
MolaKule
Staff member
Or one can design a transmission with more clutch plates/pressure plates, or larger clutch plates/pressure plates to handle the increased torque.
With manual transmissions you could push a trailer backwards all day at 2-3 miles per hour (so without fully engaged clutch) and never wear out a clutch. Just don't add throttle either, and let the idle speed regulation do the work
Or you could do it bad and burn out a clutch in minutes or even seconds....
Or you could do it bad and burn out a clutch in minutes or even seconds....
A lot of the new compact tractors have dry clutches and its not uncommon for someone to burn them up quite quickly as they are used to using/abusing it like its a wet clutch.
I know I'm a fan of the wet clutch in my ATV, it seems to survive quite well with all the abuse it gets.
I know I'm a fan of the wet clutch in my ATV, it seems to survive quite well with all the abuse it gets.
Originally Posted By: Jetronic
With manual transmissions you could push a trailer backwards all day at 2-3 miles per hour (so without fully engaged clutch) and never wear out a clutch. Just don't add throttle either, and let the idle speed regulation do the work
Or you could do it bad and burn out a clutch in minutes or even seconds....
I get your drift, and will explain how they work, and why you are nearly sort of correct.
The power transfer across a clutch is a "torque in = torque out" (torque converters have a multiplier effect, clutches are straight equal torques).
The power into the clutch is the torque x engine RPM.
The power out of the clutch is the torque x gearbox input shaft RPM.
The difference is that power that's being used to fry the clutch.
i.e. clutch frying power = applied torque x RPM difference (times 2 x pi/60, which we don't need to worry about here).
Your engine typically doesn't produce much torque at no revs, so needs some revs to match the tractive effort, and those revs create greater power loss through the clutch, and at a higher applied torque also.
So yep, you are really close.
My Nissan diesel had a LOT of EGR just off idle, and a "swirl control" butterfly that cut off one of the two inlet valves per cylinder to provide better mixing...it needed great gobs of revs and a clutch dance to get moving on a 1:10 gradient. No EGR and swirl valves later, you can let it out quickly at idle and away she goes...much much better for the clutch, maybe not so good for the big ends.
With manual transmissions you could push a trailer backwards all day at 2-3 miles per hour (so without fully engaged clutch) and never wear out a clutch. Just don't add throttle either, and let the idle speed regulation do the work
Or you could do it bad and burn out a clutch in minutes or even seconds....
I get your drift, and will explain how they work, and why you are nearly sort of correct.
The power transfer across a clutch is a "torque in = torque out" (torque converters have a multiplier effect, clutches are straight equal torques).
The power into the clutch is the torque x engine RPM.
The power out of the clutch is the torque x gearbox input shaft RPM.
The difference is that power that's being used to fry the clutch.
i.e. clutch frying power = applied torque x RPM difference (times 2 x pi/60, which we don't need to worry about here).
Your engine typically doesn't produce much torque at no revs, so needs some revs to match the tractive effort, and those revs create greater power loss through the clutch, and at a higher applied torque also.
So yep, you are really close.
My Nissan diesel had a LOT of EGR just off idle, and a "swirl control" butterfly that cut off one of the two inlet valves per cylinder to provide better mixing...it needed great gobs of revs and a clutch dance to get moving on a 1:10 gradient. No EGR and swirl valves later, you can let it out quickly at idle and away she goes...much much better for the clutch, maybe not so good for the big ends.
but for the big ends, you could go up in HTHS
all in all though, the torque (or pressure on the big ends) at idle is low compared to when the turbo is spinning higher in the rev range. I know, RPM is also low...
all in all though, the torque (or pressure on the big ends) at idle is low compared to when the turbo is spinning higher in the rev range. I know, RPM is also low...
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So if cutting torque and rev matching can keep the friction material lasting forever, why do we still have transmission that grenade in the 2000s?
Originally Posted By: PandaBear
So if cutting torque and rev matching can keep the friction material lasting forever, why do we still have transmission that grenade in the 2000s?
The ECM controlled trannies indeed do cut the power when shifting, but you question about why do trannies still grenade in the 2000s. Trannies still grenade these days for the same reason they grenades 50 years ago,, poor quality. These days CAD allows the engineers to move the level of quality to a minimum spec or performance.
So if cutting torque and rev matching can keep the friction material lasting forever, why do we still have transmission that grenade in the 2000s?
The ECM controlled trannies indeed do cut the power when shifting, but you question about why do trannies still grenade in the 2000s. Trannies still grenade these days for the same reason they grenades 50 years ago,, poor quality. These days CAD allows the engineers to move the level of quality to a minimum spec or performance.
MolaKule
Staff member
Originally Posted By: PandaBear
So if cutting torque and rev matching can keep the friction material lasting forever, why do we still have transmission that grenade in the 2000s?
1. Not using the tranny for its intended purpose; use a purpose-rebuilt TH350 or TH400 for racing or heaving towing,
2. material and material treatment QC; in the past Sungear and clutchpack splines had poor hardening of splines or improper alloying of material.
3. Following OEM stated fluid replacement regimes for 100,000 miles;
no mention of changing after break-in or replacing fluid before the 100,000 mile magic mark.
Look the modern fluids are exceptional compared to fluids of the 70's through 90's, but they are not quite yet 100,000 mile fluids.
So if cutting torque and rev matching can keep the friction material lasting forever, why do we still have transmission that grenade in the 2000s?
1. Not using the tranny for its intended purpose; use a purpose-rebuilt TH350 or TH400 for racing or heaving towing,
2. material and material treatment QC; in the past Sungear and clutchpack splines had poor hardening of splines or improper alloying of material.
3. Following OEM stated fluid replacement regimes for 100,000 miles;
no mention of changing after break-in or replacing fluid before the 100,000 mile magic mark.
Look the modern fluids are exceptional compared to fluids of the 70's through 90's, but they are not quite yet 100,000 mile fluids.
So if I understand correctly. It is not really a "wear" issue but rather an "oops" issue in design that prevents a long life, and a correctly designed tranny used correctly should last longer than the rest of the car.
automatic transmissions is another thing. there's a lot of brakes and clutches in there, but if used properly they should indeed last a long time.
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