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Discussion Starter #1
Thought I'd share some of the info found searching the web for the Xtronic Continuously Variable Transmission (CVT) used in the MO.

Although it's not the Xtronic, the JATCO toroidal is the "Nissan Xtroid". Here is an interesting read on the maker of both CVT's, namely JATCO. Unfortunately their site provides a lot of detail on the toroidal CVT but not the Xtronic.

A white paper was presented at the Japan Society Of Automotive Engineers on the JATCO belt drive CVT3 designed for a front wheel car with 3.5L ie MO. But I can't find the actual document! There are also a few interesting reads at the Engineering Tips Forums.

My original objective was to find HorsePower or Torque ratings on the MOs CVT. Unfortunately I never found it. I'm not looking to improve the HP on the Murano. I am just curious about the CVT. No engineer ever designs without margin, at least not for very long. I'm just wondering how much margin. From my research, the change in the belt and cone materials and most importantly the fluid led to the development of the JATCO CVT3. Fascinating stuff.

Nissan is being careful not to over emphasize the CVT in their marketing of the Murano even though they have spent lots of money in the development of the technology over a couple decades, have used it for years in "foreign" markets, and some racing. I believe the reluctance is not due to the engineering, I believe it's due to the "American Market". Our reluctance to embrace new ideas, especially given the Subaru experience. We tend to not let the facts get in the way, urban legends are much more important after all.
 

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Enforcer,
Thanks for the links. It makes very interesting reading. Definitely we are living in interesting times. CVT or IVT – does not really matter to me. I love the feeling CVT delivers. I hope the reliability will be also there.
 

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Discussion Starter #3
Me too Kris. I think it's interesting to note from the JATCO site that the CVT3 is relatively new. Although the technology has been out there for quite a while, getting to the 3.5L class is relatively new let alone FWD. In other words, steel belt CVTs have been in service a long time, just not in the 3.5L class. Another interesting concept is they use engine displacement as a class or category instead of HP or torque. Yes you could say that displacement general refers to a HP...but not exactly. Especially when you start talking VVT, dual overhead cam, 10.3:1 CR and moly coated pistons. Anyhow, the point is not all 3.5L engines deliver the same max HP/torque and depending on bore and stroke, at various rpms. Not to mention if the next VQ35 gets VVLT. Anyhow, if you run into any other info, let us know!
 

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That does make for interesting reading.
I can attest to the fact that that post was not listed here under general discussions.
When I joined, I read every single post in every single thread.
I would have jumped on a thread about the CVT (And did).

Cyberspace, indeed.

Homer
 

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I posted a bunch of stuff on this in the beginning of the year at freshalloy.

I may still have that article you can't find.

Let's see....

Ah... I'll have to dig deeper.

I did find something I captured on a CVT that is directly related to the Murano's


Nissan, accompany with its partner Subaru, is widely
regarded as the leader in CVT technology, especially
after it launched M6 Hyper-CVT in the Japanese
Primera.
M6 Hyper-CVT could be described as "the Tiptronic
in the CVT world". Apart from fully auto mode like all
CVTs, it provides a manual mode which simulates a
6-speed manual gearbox. Of course, in theory it can
simulate more ratios, but no driver will ask for more
than they can cope with.
Even if you ignore this trick, it was still the most
advanced CVT of its time. Mated with Primera's 2-
litre dohc VVT engine, M6 Hyper-CVT handles 190
hp and 150 lbft, a record of its time. It also delivers decent smoothness and response, thanks to the use
of torque converter (like automatic transmission) instead of conventional electromagnetic clutch.
 

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There is a very good article on the AWD and CVT systems on the Murano on the Fresh Alloy site. Not on their BBS but as a separate link from their Murano specific review page. Check it out.

The description of the AWD system (they call it all new, and that article was from 2002) suggests that the "new AWD" system we read about in Nissan's press release refers to the current AWD in all Muranos.
 

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Discussion Starter #11
And here is a list of links on this forum of CVT related discussions:

http://www.nissanmurano.org/forums/showthread.php?s=&threadid=1119
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=1115
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=1088
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=986
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=853
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=826
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=799
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=740
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=711
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=692
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=648
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=638
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=627
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=580
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=562
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=549
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=510
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=391
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=274
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=98
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=88
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=86
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=77
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=29
http://www.nissanmurano.org/forums/showthread.php?s=&threadid=22
 

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The January issue of Road and Track has an article about CVT transmissions. Audi A4, Saturn Ion, Toyota Prius, Honda Civic Hybrid, BMW Mini, and the Murano all have a version of the CVT transmission . The Audi has a 6 speed version that you can manually shift if you wish. I assume the 2004 Murano SE CVT operates in a similar fashion to the Audi.
 

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Enforcer, Is there MPEG, AVI or QuickTime on the web showing the CVT operation? Despite reading, it's hard to imagine the whole thing in operation and a video would help out alot. Thanks, MOjoe
 

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Has anyone driven the new 2004 Murano SE and compared its manual shifting CVT with the Murano SL CVT ? What are your impressions and which version do you prefer ?
 

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Discussion Starter #18
Out of the blue you occasionally get an email that is actually worth while and not a load of spam. That happened to me recently. Out of the blue I received an email and some documents from a person that visited my website. I will not post or email the proprietary documents or this persons contact info, it would not be right to put someone on the spot and take their info out of context. This person has been very gracious answering my questions. So I will share some of the questions and answers.

The first document talks about the Van Doorne push-belt CVT with reference to the one used in the Murano. It talks about the materials and processes used and how to maximize them given the finite element analysis of stresses and test data. Good enough to know that a lot of science and engineering went into the CVT. The second document was a brochure showing all the vehicles that currently use CVTs. They are quite common and have been for years overseas, pertinent info posted on my website. The last document talks about a prototype CVT for V8s (580Nm+). Bottom line it worked and we could start seeing them in vehicles as large as the GMC Yukon.

Here are some of the questions I asked and the replies:

Q: The max belt tension is 500Nm and the engine currently produces 350Nm+. So if engine modifications are performed that increase the power output, does this effectively result in a shorter lifetime of the belt?

A: The belt is designed based on a certain load collective. In case you increase the power output of the engine and actually use this extra power a lot you will change the load collective and consequently change the life time of the belt.

Q: And I doubt it is this simple, but does it mean the CVT is capable of something less than 500Nm? IE the margin on the CVT is 150NM?

A: The CVT is capable of a lot more but it is a trade off between lifetime and torque capacity. We have even put it in a Formula one vehicle that was tested by David Coulthard in 1993. The belt lasted about two races. The CVT system was however not allowed to be used in the race. At this moment the 350 Nm is kind of a maximum torque capacity for commercial available vehicles of which your Murano is a nice example. We are working to increase this number. The reason why it must be able to handle 500+ Nm is that the Murano has got a torque converter that is able to amplify the engine torque to these levels. The time share of this event in the load collective is however small.
The 350 Nm does outnumber the chain that is used by Audi (maximum 310 Nm and no torque converter so no torque amplification).

Q: How does one derive the predicted lifetime of the belt if a constant 350Nm is applied? Am very interested in this one as I am preparing to tow a trailer right at the 3500lb TOW rating of the Murano for 700 miles in one day.

A: Unfortunately there is no simple formula for this one. It depends on a lot of factors. In case you stay within the margins described in your manual you are safe.

Q: Am I correct in assuming that the CVT is designed such that the belt does not slip with respect to the pulleys?

A: Technically speaking the belt always slips because of the tribological nature of the contact between belt and pulley. We call this microslip. In case it becomes macroslip it becomes a problem and damage can occur. The pressure force is controlled in a way that macroslip can not occur by using a certain safety factor.
(A nice paper on this subject is SAE paper number 980822 from Nissan, available at www.sae.org)

Q: Am I correct in assuming the CVT controllers are designed to prevent jerk? In other words, what holds the belt in place is static friction which means the CVT can handle velocity and acceleration but not jerk which might overcome the static friction force and cause the belt to slip with the resulting dynamic friction, heat buildup and materiel weakening/loss?

A: The controllers are designed to handle jerk coming from the engine side. Jerk coming form the road side is handled by the clamping safety (see above).

The first document was released during the VDI 2002 CVT congres in Munich Germany (VDI No 1709, ISBN 3-18-091709-1).

Additional SAE papers (these can be obtained from the site www.sae.org at some cost) about CVT's in the Nissan Murano, Primera, Saturn Vue and Ford Focus:
Primera : 980823
Toyota : 2000-01-0872
ZF :2000-01-0873
Murano : 2003-01-0593
Saturn Vue : 2003-01-0593

References:
[1] Brandsma, A., van Lith, J,. Hendriks, E., "Push belt CVT developments for high power applications", Proc. of CVT99, Eindhoven University of Technology 1999, pp.142-147.
[2] van der Sluis, F., Brandsma, A., "Stress reduction in push belt rings using residual stresses", Proc. of CVT2002, VDI, Munich 2002, pp.383-402.
[3] Stockton, T., "The Ford research dual mode Continuously Variable Transmission”, Proc. of SAE 1984, SAE841305.
[4] Markland, E., Comerford, K., "Dual mode improves CVT efficiency”, Professional engineering, July-August 1991, pp. 27-28.
[5] Mucino, E., et al., "A continuously Variable Power Split Transmission for Automotive Applications”, Proc. of SAE Detroit 1997, SAE970687.
[6] Heitmann, A., et al., "Das i2 Getriebe für den Autarken Hybrid”, Proc. of VDI, 1995, VDI Berichte nr 1225 pp. 101-114.
 

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