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Sorry if this has been addressed before . . .

What exactly does putting the transmission in 'S' mode do? I understand from the manual that it increases "engine braking" . . . which is obvious when it is engaged. It also seems to act as a 'sport' mode which I have had in other cars. While going about 60mph today I threw it into 'S' mode and the revs moved up substantially. Is it OK to do this? Or is it meant more for slower speeds?

Any commentary on the uses of the 'S' mode would be appreciated!!

Thanks. Hoping everyone has a wonderful and safe holiday season!

lawbroker
 

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Its a transmission mode in which the TCU keeps the RPM's at a higher level (at or above ~4000rpm) than D, giving you more engine braking, and more power too. I wouldn't use it all the time though, as the CVT's rated life is a measure of the total load on the belt over time - higher RPM = higher collective load.
 

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> higher RPM = higher collective load.

Um...hmmm....it's making my head hurt trying to think about pulley velocities and how it changes with speed and RPM... What is your thinking with that statement?

Clutches on manual trannys always start to slip in the highest gear and then on down becuase the motor & drive line has the most difficult time accelerating the vehicle due to the gearing ratio in top gear. If one extrapolates from that, the CVT should be under the least strain when RPMs are high, because it's not having to deal with the motor's torque fighting with the very tall gear ratio.

Does that make any sense at all? :confused:
 

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Mr. 3 K, 3/3/5. 5K,10/5/7
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Does to me, That why I feel that the towing capacity of the MO, (which I think requires the most torque when getting off the line) indicated that the our CVT actually has some good margins of safety.

Ft - lbs ( Torque) times feet per minute (RPMs) essentially equals horse power ergo For the same power output higher rpm requires lower torque.
 

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Carl - your right that clutch slippage generally occurs in high gear in manual transmissions...remember, however, most transmission damage(gear breakage / u-joint breakage) happens in low gear due to the multiplied torque and power applied to the "back end" of the drivetrain....as the CVT acts as both the clutch(torque converter)and the transmission, high rpm starts in low gear(small diameter input pulley/large diameter output pulley) puts maximum pressure/strain on the steel belt because of the high multiplication of engine power /torque...this is why full engine power is not allowed until after the MO gets rolling.....now my head is starting to hurt...
 

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From what I understand, the CVT is mainly limited by the amount of torque the belt can handle. This is why the engine is limited to 245hp when Nissan can easily top the competition with the 260hp version of the VQ. Not much technical information is known about the CVT, but we do know that a higher torque load will wear the belt quicker. My understanding is that higher engine RPM = the more torque applied to the belt over a certain time period (i.e. power). I would assume this wears the belt more quickly.

If you really think using Ds will result in less load to the belt, then by all means use it! Carl, I understand what you are saying, and it makes sense to me. However, we're gonna need a JATCO engineer to tell the official answer to us!
 

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Mr. 3 K, 3/3/5. 5K,10/5/7
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I don't want to be rude and I do humbly suggest that I have done that by making a rather low key analogy.

Some a slightly differing perspective, When the SAME amount of HP is delivered at higher RPM it is done so with a lower torque. The limit on the band of the Jacto or any of the other "belt drives" (generic term) is how much tension the bands can take or transmit. This tension is essentially equal to torque. The driven "Pulley" diameter is allowed to increase at higher RPM for the equivalent HP being transmitted. This reduces the tension on the Band. , While not an official "JACTO" factory Engineer I sure know the arena and have "Hands on" experience in this area. .

We are all entitled to our opinions and I certainly do not want to be argumentative or be contentious so please feel free to further state your case without concern of offense as I will not take any.
 

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None ever taken. ;)

I do understand what you are trying to say. It makes sense that if total power output is the same at different pulley ratios, then it follows that the higher ratio would be a case where less torque is being put onto the belt.

Even if the CVT belt can handle the sustained high RPMs, I wonder if the rest of the internals can.
 

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Mr. 3 K, 3/3/5. 5K,10/5/7
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Now thats a good question, I sure don't know, maybe thats also part of the rev limiter's function?
 

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The CVT belt is not in tension but in compression, ie the belt is being pushed, not pulled. There should be less force on the belt in DS mode because for a given speed higher engine rpms means a lower gear ratio and lower gear ratios require less torque to turn the pulleys. Like stated above, for a manual transmission higher gears put more of a strain on the clutch or in this case more force trying to "slip" the belt on the pulleys. If you pedal a ten speed bike in high gear you are putting much more effort into the pedals than you would in a lower gear where you pedal faster but it is not as difficult.
 

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HuskyFan said:
The CVT belt is not in tension but in compression, ie the belt is being pushed, not pulled. .
Hmm, unless the CVT has a freewheel (bicycle chain analogy) wouldn't half the belt be in compression and then the other half be in tension ? Again in bicycle analogy like a "fixed gear" ?
 

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This may just be a brain fart, but:

Wouldn't the total load on the belt be similar for all ratios? There is force transmitted to the belt from the engine side and force transmitted from the belt on the wheel side. If there is less strain on the engine side due to lower ratio, there should be more strain on the wheel side.

Since it's all on the same belt, there is no difference between different ratios.

If any of this makes sense, then the only thing that matters is engine output.
 

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Mr. 3 K, 3/3/5. 5K,10/5/7
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May I suggest the following as "some" good reading on this subject.

http://cvt.com.sapo.pt/why/why_cvt.htm

http://www.sae.org/automag/globalvehicles/05-2002/page2.htm

http://www.baileycar.com/2003_murano_html.html

http://old.lib.ucdavis.edu/pse/cvt04/papers/04CVT-55.pdf


While it's called a push belt beacuse the plates on the belt are in compresssion a good analogy is like pushing on a stack of dominos held together with a belt, when the dominos try to slip side to side or the stack wants to bend or fall over the belt holds them from doing that and this is what produces the "tension in the belt" it not the belt pulling the pullies but the belt holding the stack of disks stright.

Lest torque transmitted, less load, less belt forces, less tension.
 
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