dropping out of VTEC when shifting
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From: Longmont, CO
Originally Posted by negcamber' date='Mar 23 2007, 09:58 AM
Again...this is very easy to prove to yourself. Lets modify the coin experiment a bit:
Take a CD and place it on your desk. Use your fingers to turn the CD. You have no problem turning it, correct?
Now take the coin again and turn it with your fingers with the smallest amount of downward pressure that you can and still make the coin turn.
So you have proved to yourself that you can generate enough torque to turn both, correct?
Now place the coin in the center of the CD. Use as close to the same downpressure as before to turn the coin. Does the CD turn too? Maybe a little but not with the same rotational velocity as the coin. Why isn't the CD turning? You proved earlier that you can generate the torque needed to spin both the CD and the coin. So where is all the power that you are producing going when you spin the coin? Is it going into the CD? Can't be, if it were then the CD would spin at the same rate as the coin.
The coin is the flywheel...the CD is the clutch. If the clutch is not spinning at the same rate as the flywheel then there is power loss to the drivetrain...power which would otherwise be making it through the drivetrain if the clutch were not slipping.
Take a CD and place it on your desk. Use your fingers to turn the CD. You have no problem turning it, correct?
Now take the coin again and turn it with your fingers with the smallest amount of downward pressure that you can and still make the coin turn.
So you have proved to yourself that you can generate enough torque to turn both, correct?
Now place the coin in the center of the CD. Use as close to the same downpressure as before to turn the coin. Does the CD turn too? Maybe a little but not with the same rotational velocity as the coin. Why isn't the CD turning? You proved earlier that you can generate the torque needed to spin both the CD and the coin. So where is all the power that you are producing going when you spin the coin? Is it going into the CD? Can't be, if it were then the CD would spin at the same rate as the coin.
The coin is the flywheel...the CD is the clutch. If the clutch is not spinning at the same rate as the flywheel then there is power loss to the drivetrain...power which would otherwise be making it through the drivetrain if the clutch were not slipping.
) In that case, the engine's entire energy output goes into creating heat due to the friction.But that's not at all what happens during a gear change. Minus a small part going to waste heat due to friction, the engine's entire energy output is going towards spinning up the drivetrain. That's why the rpms fall, at the same time the car gains speed.
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From: Jacksonville, FL
Elstain...we will have to agree to disagree. There are no "two types of clutch slipping". Either the clutch is slipping or it is not. Does not matter if you are slipping the clutch purposefully or accidently when launching or if the clutch slips when shifting gears. So long as the flywheel is spinning faster than the input shaft, the clutch is slipping and power that the engine is making is not being transferred.
There are quite a few racers in your area..and based on your avatar I'll assume you hang out with some. Not to mention the guys from Temple of VTEC out there. Ask some of the ones who you feel are more knowledgeable.
Or perhaps you can explain to me how a slipping clutch is transferring the same power that a non-slipping clutch does. Because that is what you are saying...a slipping clutch is transferring nearly all the power the engine is making to the input shaft even though the flywheel is spinning faster than the input shaft (which is the definition of clutch slip).
There are quite a few racers in your area..and based on your avatar I'll assume you hang out with some. Not to mention the guys from Temple of VTEC out there. Ask some of the ones who you feel are more knowledgeable.
Or perhaps you can explain to me how a slipping clutch is transferring the same power that a non-slipping clutch does. Because that is what you are saying...a slipping clutch is transferring nearly all the power the engine is making to the input shaft even though the flywheel is spinning faster than the input shaft (which is the definition of clutch slip).
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From: Longmont, CO
You suggest I go hang out with some other racers - perhaps I can suggest you go hang out with some thermodynamicists?
Granted, clutch slip is clutch slip, I agree there. But it's what the clutch slip leads to that are two completely different scenarios.
Scenario one: You redline in 3rd gear and shift into 4th. The clutch slips and never grabs. You stay on the gas and the engine zings to redline and starts bouncing off the rev limit. This is, without a doubt, SLOW. The car doesn't accelerate, and probably even starts to slow down. Another way to think of it - with the rev-limit in action, the engine probably makes only a handful of horsepower. Hard to accelerate when you're only producing 10hp (or however much little hp is required to hold the engine at 8200rpm.)
Scenario two: You redline in 3rd gear and shift into 4th. Due to CDV or heavy flywheel, the clutch takes some time to engage. During this time, you're at full throttle but the engine revs still fall as the clutch engages. This is happening from about 7500rpm down to 6500rpm or so, therefore the engine is producing about 225 to 200hp. ALL of that energy (minus friction loss to heat) is going into speeding up the drivetrain. It's obviously not speeding up the engine! That's slowing down! It's a question of transfer of energy - that 200+ hp doesn't just go away.
Granted, clutch slip is clutch slip, I agree there. But it's what the clutch slip leads to that are two completely different scenarios.
Scenario one: You redline in 3rd gear and shift into 4th. The clutch slips and never grabs. You stay on the gas and the engine zings to redline and starts bouncing off the rev limit. This is, without a doubt, SLOW. The car doesn't accelerate, and probably even starts to slow down. Another way to think of it - with the rev-limit in action, the engine probably makes only a handful of horsepower. Hard to accelerate when you're only producing 10hp (or however much little hp is required to hold the engine at 8200rpm.)
Scenario two: You redline in 3rd gear and shift into 4th. Due to CDV or heavy flywheel, the clutch takes some time to engage. During this time, you're at full throttle but the engine revs still fall as the clutch engages. This is happening from about 7500rpm down to 6500rpm or so, therefore the engine is producing about 225 to 200hp. ALL of that energy (minus friction loss to heat) is going into speeding up the drivetrain. It's obviously not speeding up the engine! That's slowing down! It's a question of transfer of energy - that 200+ hp doesn't just go away.
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From: Jacksonville, FL
Sorry if you took my comment about asking racers in your area the wrong way. It's obvious you do not believe/understand me, but perhaps if you ask some of the folks in your area who you trust to have more knowledge than yourself, then maybe you will accept the answer.
As far as the "thermodyamiscist" comment...I do have a masters in engineering...although I admit not a very tough engineering field and my thermo classes were limited to those in undergrad.
However...please school me. So far your explaination of how all of the engine's power is making it to the input shaft if the flywheel is spinning faster is not robust enough.
As far as the "thermodyamiscist" comment...I do have a masters in engineering...although I admit not a very tough engineering field and my thermo classes were limited to those in undergrad.
However...please school me. So far your explaination of how all of the engine's power is making it to the input shaft if the flywheel is spinning faster is not robust enough.
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From: Longmont, CO
Originally Posted by negcamber' date='Mar 24 2007, 10:22 AM
Sorry if you took my comment about asking racers in your area the wrong way. It's obvious you do not believe/understand me, but perhaps if you ask some of the folks in your area who you trust to have more knowledge than yourself, then maybe you will accept the answer.
As far as the "thermodyamiscist" comment...I do have a masters in engineering...although I admit not a very tough engineering field and my thermo classes were limited to those in undergrad.
However...please school me. So far your explaination of how all of the engine's power is making it to the input shaft if the flywheel is spinning faster is not robust enough.
As far as the "thermodyamiscist" comment...I do have a masters in engineering...although I admit not a very tough engineering field and my thermo classes were limited to those in undergrad.
However...please school me. So far your explaination of how all of the engine's power is making it to the input shaft if the flywheel is spinning faster is not robust enough.
I believe I understand what you're saying - the penny/CD example makes perfect sense. However, I don't think you understand that's NOT the scenario I'm talking about. Your example is like the situation of a clutch TOTALLY slipping and the revs zipping up to fuel cutoff. Which is NOT what's happening during a slow clutch engagement.The fact that the engine's revs are falling while it's at full power is direct evidence that a significant amount of the engine's energy is being transfered to the drivetrain.
Would you agree that the 200+ hp the engine is producing is going somewhere?
It's obviously not speeding up the engine - it's slowing down. Some is being lost as heat due to friction, but my belief is that it's not much. So where's the rest of it going? Into speeding up the drivetrain!
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From: Dry Branch
Negcamber and Elistan:
I've been following this discussion for some time, and it seems to be that you are both mostly correct. Let me take a shot at this.
First, anytime the clutch slips heat is generated. The heat is lost energy that could have gone into accelerating the car if the clutch had not slipped. This is true any time the clutch slips. However, when accelerating up through the gears and shifting very quickly, the clutch gets released before the flywheel has slowed to match the speed of the clutch disk. As the clutch is engaged the flywheel is slowed, and most of it's energy goes to the clutch disk and onward to the rear wheels. This is why the back tires will chirp on a quick 1-2 shift at redline. As the clutch engages with the flywheel spinning quicker than the clutch disk the clutch does slip, until the speeds match, so some of the energy in the flywheel is lost to heat, but not all of it. You get the quickest acceleration when you shift quickly and make good use of the extra boost you can get from keeping the engine spinning during quick shifts. So you actually do get the fastest acceleration when the clutch slips a bit after a quick shift. In contrast, a rev-matched shift will produce little or no clutch slip, and won't unbalance the car; Great when cornering but not so great when accelerating in a straight line.
I've been following this discussion for some time, and it seems to be that you are both mostly correct. Let me take a shot at this.
First, anytime the clutch slips heat is generated. The heat is lost energy that could have gone into accelerating the car if the clutch had not slipped. This is true any time the clutch slips. However, when accelerating up through the gears and shifting very quickly, the clutch gets released before the flywheel has slowed to match the speed of the clutch disk. As the clutch is engaged the flywheel is slowed, and most of it's energy goes to the clutch disk and onward to the rear wheels. This is why the back tires will chirp on a quick 1-2 shift at redline. As the clutch engages with the flywheel spinning quicker than the clutch disk the clutch does slip, until the speeds match, so some of the energy in the flywheel is lost to heat, but not all of it. You get the quickest acceleration when you shift quickly and make good use of the extra boost you can get from keeping the engine spinning during quick shifts. So you actually do get the fastest acceleration when the clutch slips a bit after a quick shift. In contrast, a rev-matched shift will produce little or no clutch slip, and won't unbalance the car; Great when cornering but not so great when accelerating in a straight line.
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From: Jacksonville, FL
Thanks for weighing in Red...
Absolutely, it is rare to completely eliminate slip when shifting. However nornally the clutch slip on up shift is extremely short lived as the clutch catches up very quickly.
For the AP2...at redline in 1st, the corresponding rpm in 2nd is ~5200rpm. And we can see in the video that the engine is spinning at 6k+ when shifting 1-2 with the CDV in place. So there is at least 800rpm differential between the flywheel and the clutch.
So the question is...how much power loss is there when the clutch is slipping that much. Elistan says almost none (aside from heat transfer) and I don't see how that is possible with that much slip.
Elistan...to your question on where is the energy going: Answer this...when the clutch pedal is pressed and you rev the engine, where is all the power going? Is it going into the drivetrain? No...it is going into spinning the flywheel...nothing more. And that is what is happening when the clutch is slipping. Yes, SOME of the power is going into the clutch and allowing the clutch to increase in speed to catch up with the flywheel speed...but not all of it (and honestly the heat loss is insignificant). Quite a bit of the power is being spent on spinning the flywheel only.
Absolutely, it is rare to completely eliminate slip when shifting. However nornally the clutch slip on up shift is extremely short lived as the clutch catches up very quickly.
For the AP2...at redline in 1st, the corresponding rpm in 2nd is ~5200rpm. And we can see in the video that the engine is spinning at 6k+ when shifting 1-2 with the CDV in place. So there is at least 800rpm differential between the flywheel and the clutch.
So the question is...how much power loss is there when the clutch is slipping that much. Elistan says almost none (aside from heat transfer) and I don't see how that is possible with that much slip.
Elistan...to your question on where is the energy going: Answer this...when the clutch pedal is pressed and you rev the engine, where is all the power going? Is it going into the drivetrain? No...it is going into spinning the flywheel...nothing more. And that is what is happening when the clutch is slipping. Yes, SOME of the power is going into the clutch and allowing the clutch to increase in speed to catch up with the flywheel speed...but not all of it (and honestly the heat loss is insignificant). Quite a bit of the power is being spent on spinning the flywheel only.
