Maximam

The '07 Maxima with the CVT could in fact be faster than the '04,'05 & '06 with the automatic. The CVT is more efficient when putting power to the ground. I am curious to know the outcome.

"Steel belt CVT's can approach 97% efficiency, similar to manual transmissions. Conventional automatic transmissions typically have efficiency in the 80% range. The increased efficiency and always-correct gear ratio enables CVT equipped vehicles to achieve up to 10% better fuel economy, lower engine emissions, and faster acceleration compared to conventional automatics."

Jeff92se

iTrader: (82)

There always has to be some slip assoc w/ an torque convertor type auto? But having infinite amount of gear ratios probably balances that out.

Plus autos can brake torque at the line

Nissan 6

Very interesting info, I was suprised at how efficient it is too.

NismoMax80

iTrader: (6)

thought this was common knowledge about CVT and why Nissan is favoring them?

our Auto is closer to the manual and the CVT should be just as close.

NmexMAX

iTrader: (22)

How would you dyno one of those *****... Use 'manual' mode

willysmooo

it is the same transmission as my snowmobiles. One thing is that they are super easy to work on and rarely have problems associated with them. Since these types of transmissions are infinitely variable they provide a much wider band of power at all speeds. If i had one I would feel completely comfortable working on it and there are many ways in which to adjust the system for better response and performance.

jcalabria

Yeah, but I am guessing that the snowmobile CVT is not so heavily computer controlled. How well a powerful CVT equipped car performs is almost completely dictated by the CVTs program mapping. I mentioned in an earlier post... I see a market emerging for "chipping" CVT trannies. Then we will find out how "close to the edge" the CVT durability is with engines like ours. I'm thinking a lot of the CVTs behavior and interraction with the drive-by-wire throttle is aimed at keeping the CVT intact. If you read the manual, there are a variety of fail-safe modes it will go into when subject to harder treatment or environmental conditions.

FYI - I have noticed one little anomaly in the CVT operation... if you are cruising at light throttle at 30~40 mph, and let off the gas, the car will engine brake like a manual for about 2 seconds, then it will noticeably free up and coast. Not sure if its the ratios shifting or the TC unlocking (more likely). Its not terribly annoying, but it is noticeable.

HGN2001

I've noticed that in my '07 too. It'll take a little getting used to.

Harry

madmik

iTrader: (1)

In theory, it should be faster : 97% efficiency, no gear shift delay, but will/should run in the best torque range. The belt should last a long time since it does not get the jolt of gear shifts.

I had snowmobiles and moped with rubber CVT in a previous life. I love the concept but hate the feeling. Its like having a diesel in an F1. The end is near for the car enthusiast.

scubasteve

iTrader: (6)

few threads down is a good discussion on these =]

SilverMax_04

I agree with the thought: "The end is near for the car enthusiast" with the coming demise of the 6-speed manual trannie.

I understand how a normal auto trannie stays in gear while stopped at a stoplight -- the torque converter slips and allows the car to stay in gear. The slippage in the torque converter is where all of the efficiency loss exists in these transmissions. (History note: Torque Converters are just more efficient versions of the old Chrysler "fluid drive" from the early 1950s -- they not only slip but they "multiply torque.")

I don't understand how a CVT trannie "stays in gear" while the car is stopped. Can anyone here explain the physics of this ability to me? Is this "slippage" in a CVT one of the sources of the reported "heat problems" for these new trannies? If not, then what causes these "heat problems" -- or is this a fiction that does not exist?

In another thread there is this statement by an 07 owner: "The tranny dipstick is there but its got a sealed cap on it with a warning not to let anyone but Nissan touch the fluid." What kind of fluid is there in a CVT? And why is it so sealed up?

lightonthehill

SilverMax_04 - I think you are correct that there have been some heat-related problems during the development of the CVT. But after the horrible fiasco Accura had with the TL tranny, I would find it difficult to believe Nissan would risk putting a CVT in ALL Maximas unless they were convinced they had the heat problem licked. That would be beyond risky.

I have also noticed that when I let off the gas when headed downhill, compression holds the car back for a short period, then seems to release. And this is in an '04 SL with 5 speed auto.

jcalabria is right-on that the whole key to the CVT is the computer control system. The CVT could be mechnically perfect, but unless the computer is programmed 'just right', the performance will not be there. The big question is defining exactly what 'just right' really is. I am one who is excited about the potential of the CVT.

And the thread-starting post reinforces what many (including me) have been saying here all along: the basic laws of physics would suggest that a tranny with no breaks in speed or accelleration due to gears shifting would theoretically have an advantage over one that did shift.

But I still wish Nissan had kept a 6 speed option available for long-time Maxima aficionados, even if only in two or three exterior colors; maybe black, white, and a re-release of Burnt Ember?

jcalabria

In automotive applications (at least Nissan's) there is still a TC in front of the tranny just like a conventional automatic. The steel belt & pulleys are always "engaged".

The fluid is part of the basic TC function, plus it provides lubrication for the steel belt and other internal parts. The fluid used is critical because its characteristics determine how the belt and the pulleys interract, including control of the heat generated by the friction between the belt and pulleys.

Here's a cutaway of the Jatco CVT used in the Murano & Maxima:



Actually, looks a lot simpler than a conventional planetary automatic.

And this is the steel push-belt:



There's more info to be found at http://www.jatco.co.jp/ENGLISH/PRODUCTS/cvt.html#ff

Maximam

It is a special fluid that can take ALOT of heat. Normal ATF won't do the job. The CVT creates so much heat it uses 3 coolers.

SilverMax_04

Thanks "light," jacalbria, and Maximan for answering my questions. If the CVT still has a torque converter (a surprise to me), how does it get such high efficiency?

I would still also like to know where all of the heat comes from. High heat is frequently a sign of loss of efficiency.

I also noted this "light" comment: "I have also noticed that when I let off the gas when headed downhill, compression holds the car back for a short period, then seems to release. And this is in an '04 SL with 5 speed auto." I believe the old auto trannie is set up to go into this free-wheeling mode to improve coasting and save on gas. I suspect that the CVT's torque converter also does the same free-wheeling. I frequently free-wheel my Max by shifting my 6-speed into neutral. But I can also use engine braking to slow down on hills when that ability is needed. This is why I insist on keeping max control with a manual trannie.

Jeff92se

iTrader: (82)

I'm posting this now so I can read later. Hope it helps you guys too

http://auto.howstuffworks.com/cvt.htm

NismoMax80

iTrader: (6)

^^^
that is how it "holds a gear"
visuals are so much easier than words, thanks Jeff.

when I test drove an 07, the CVT allowed me to come to a stop in "6th". not sure if there's a benefit to that, but it still worked. i had to "shift" back down to a lower "gear" to really get moving.

jcalabria

Good CVT info in this article - belts/fluids/heat etc.

http://www.canadiandriver.com/articles/jk/030402.htm

SilverMax_04

Thanks for that link. It helps explain Nissan's design. I will quote from this April, 2003 article and put some of {my comments in these brackets.} You need to remember the belt is a "steel push belt."
~~~~~~~~~~~
Nissan's new Murano SUV uses a steel push belt in its CVT. The belt technology is what makes the high torque transfer possible from Nissan's 3.5 litre V6 engine. The belt is made of a series of small plates held in position by a cable. When torque is applied to the belt as it comes off the drive pulley, the plates lock together so the belt acts as a solid link. As the belt starts to rotate around the driven pulley, there is no more torque {push energy} on the belt and it becomes flexible again. Imagine trying to push a rope {which normally does not work}. Every time you push it, it turns into a stick, but pull on it and it becomes a rope again. Sounds like magic. The oil used in this CVT is part of that magic.

Nissan is using a special oil that helps lock the steel belt to the pulleys but it also lubricates and cools the transaxle. The best way to describe the oil is that it contains "rubber molecules" that provides the grip between the belt and the pulleys. As pressure is applied to the oil, the "rubber molecules" compress, turning into a crystalline form that locks the belt and pulley together. Relax the pressure and the oil returns to its original state.

Heat is a major concern with a CVT design {as I have heard for some time}. The Nissan CVT can operate at 200 degrees C, so a special oil is needed that will not break down at these high temperatures. The Murano also incorporates three transmission coolers to prevent the oil from overheating. {As I said in an earlier post here, the existance of heat is an indication of wasted energy and reduced efficiency. This wasted energy gets dumped into 3 transmission coolers as waste heat.}

A few more parts are needed to make a functional transaxle. One clutch and a simple planetary gearset, the same as used in automatic transmissions, are used to allow neutral and reverse. Nissan has added a torque converter for smoother operation at very low speeds {this allows the engine to run in "gear" while the vehicle is stopped}. Once under way, the torque converter locks up at 18 kph {11 MPH} so the CVT belt and pulleys provide all the gear advantage.

Oil pump, a small valve body, speed sensors, and a control make up the rest of the CVT. When seen apart, it looks like there are very few pieces, but you can't see the programming that goes into the control computer. Much development and research has gone into designing control systems that provide the correct gear ratio for every driving application {and Nissan has apparently twiked these controls for the Max from the earlier version used in the Murano}. The Murano SE model also allows the driver to manually select seven different ratios so the CVT can be shifted like a 7-speed manual transmission {The reports on the Max say there are only 6 selectable "speeds"}.

Steel belt CVT's can approach 97% efficiency, similar to manual transmissions {not certain I believe this given the waste heat discussed above}. Conventional automatic transmissions typically have efficiency in the 80% range. The increased efficiency and always-correct gear ratio enables CVT equipped vehicles to achieve up to 10% better fuel economy, lower engine emissions, and faster acceleration compared to conventional automatics. The future looks promising for CVT's. Its only real competition is the new computer shifted manual transmissions a couple manufacturers are just starting to produce. {For my money the driver-shifted manual trannie is still the best bet, gives the most driver control and the most efficient -- except perhaps for engine wear due to "shift shock."}

jcalabria

Either your test drive or my car (heaven forbid!) is defective, because once I hit 5mph while coming to a stop it drops into first no matter what, and you cannot manually shift back out of 1st until you are moving again.

Anybody else got some experience? (I hate samples of two... you gotta 50/50 chance, which means you know jackshït.)

NismoMax80

iTrader: (6)

i would prefer that anyway. who wants to shift back down? try to hold it up at the gear you want when stopping. it works for the auto anyway.

i thought i stopped, but certain i was below 5mph

if i ever test the SE I'll make sure.

guimar98

It's more efficient than manual transmission:

Mechanical efficiency CVT 97%
Mechanical efficiency Automatic 80-94% (depending of speed and ratio -> average 90%)
Mechanical efficiency manual 95%

Motor HP and torque speed range use efficiency CVT 99%
Motor HP and torque speed range use efficiency automatic 5 speed 88%
Motor HP and torque speed range use efficiency manual 5 speed 88%
Motor HP and torque speed range use efficiency manual 6 speed 91%

Estimated Overall performance including shift delay

Overall performance CVT 97%
Overall performance automatic 5 speed 79%
Overall performance manual 5 speed 82%
Overall performance manual 6 speed 84%

Even if power or 2007 maxima is lower, accelaration time must be
higher.

The only point that I don't like with this technology is
the motor sound and speed during the acceleration stays
the same all the time. (because the infinite variating ratio)

I prefer that sound frequency variates for more sport feeling.
The efficiency improvement is so important...I can forget this
disavantage.

This technology will be implemented on most car in the future and
we have to change our mind about that !

jcalabria

We covered Nissan's use of a torque converter with the CVT, but not everybody does. Your question made me curious as to how the others worked without a TC. I did some research on the Audi CVT, which uses an "electronically controlled multiplate wet clutch" to couple the engine to the tranny (probably similar to the electronic clutches on some of the computerized manual boxes out there).

I have driven both 1.8T A4s, 3.0 A6s & 3.2 A4s (similar power to our 3.5 VQ) with CVTs - they work well enough, but I am thankful for the torque converter - the Audi's are sort of dead off the line without the torque multiplication effect of the TC. They may be slightly more efficient since they lock up earlier, but its a worthwhile trade-off to me, especially if the Nissan TC locks up as low as 11mph, as some of the info posted indicates.

Interestingly, the Audi control algorithm for their CVT purposely adds little "hiccups" to the ratio progressions to mimic the "shift shock" of a conventional auto. I guess women don't put on lipstick in an Audi.

SilverMax_04

It is great to quote these numbers. What I base my opinion that the efficiency of the CVT is NOT as high as the manual trannie = HEAT !

The CVT has three trannie coolers to get rid of unwanted heat. The manual trannie has NO coolers because there is so little unwanted heat produced in the transmission.

Simple physics: Gasoline is burned in the engine to produce rotational physical movement with a by-product of heat. The heat from the engine is not needed and is dumped out of the radiator. The rotational movement in the transmission also produces heat in the transmission. But the CVT needs three (count them, 3) coolers to get rid of this heat and the manual trannie does not need a cooler = because it produces substantially less heat. If energy from the engine is used to produce heat it is not used to produce rotational energy at the drive wheels = a loss of energy = inefficiency.

My conclusion, based on the simple physics discussed above, is that the CVT trannie can not be as efficient as the manual trannie. This is total efficiency and not just mechanical efficiency. If the energy used to produce heat is not used for any purpose (but dumped out of 3 trannie coolers) it is a loss of energy.

NmexMAX

iTrader: (22)

In a manual transmission, 6 speeds have greater loss (less effeciency) than 5 speeds.

SilverMax_04

That's your opinion. I don't see any reason why it should.

SilverMax_04

In my discussions about the Nissan CVT on this thread with juimar, I based my energy efficiency comments on simple physics -- loss of energy through the generation of unwanted heat. I then decided that I needed to check on these efficiencies with a friend who is an SAE Engineer.

Here is his reply to my question about CVT efficiencies {with my hopefully helpful comments in these brackets}:

"The CVT is normally used so you can stay on the optimum power band of the engine and thus reduce overall fuel consumption. This implies that you have a well matched powertrain and drive within the optimum operation envelope {for that powertrain}. Operation outside of that range will result in significant fuel economy losses. When looking at the CVT itself, according to LUK the loss is 15%."

What he is saying is that there is some overall efficiency improvement with a CVT because the engine can run essentially all of the time near its optimum operating condition -- engine RPM and other factors. But if you floor the accelerator, that will no longer be the case, because the engine can be operating at near red-line for as long as you "hold" it there. Thus, this engine efficiency improvement only applies if the proper operating conditions are maintained.

My friend then provides a web site for LUK (a European trannie maker) that describes in a technical paper a CVT they are making for Audi -- the "Multitronic." If you go to this site, LUK makes the following statements:

- This CVT "can make a significant contribution towards reducing fuel consumption."

- "In comparison with the 5-speed stepped automatic transmission, a {fuel} consumption improvement of around 9% is achieved in the European MVEG {driving) cycle." {Your CVT's fuel consumption improvement will vary depending on how your actual driving compares with this European derived fixed driving cycle.}

- "Despite the fact that the CVT has this advantage, work goes on to further improve the {CVT's} efficiency."

- "This report will discuss in detail two components {factors} which contribute significantly to {CVT} energy losses. . . 1) losses through hydraulic control and . . . 2) the mechanical losses in the variator, depending on the clamping forces." {The variator is the variable pulley arrangement that continuously changes the ratio of input shaft speed to output shaft speed.}

- "The total energy loss from the variator and the hydraulics is approx. 15% of the total energy at the transmission input shaft."

- The diagram on this page of the technical paper further splits this estimated 15% total energy loss at about 9% mechanical losses and 6% hydraulic control losses.

It is clear that this CVT is not the same as the Nissan CVT, but LUK appears to be quite proud of this trannie, and I suspect that the energy losses in the Nissan CVT are likely similar, with possibly somewhat less hydraulic loss (but this is only a guess).

Here is the LUK site that provided me with a PDF file of the LUK technical paper:

http://www.luk.de/content/media/_com..._k7_chap06.pdf

My friend then ends with this comment: "There is no free ride and a 99% {efficiency} number is way to high for any CVT, like you say -- it's the physics {that determines}."

Apparition

iTrader: (5)

It bothers me alot that this tranny is overtaking the maxima, while some of you more scientifically inclined or those who like autos may be greatly intrigued, I am not.. it is an interesting technology right up to the point where Nissan thinks they can better it over the 6MT. Part of the fun in having a manual is knowing that the cars performance depends heavily on how well the driver is skilled. With the loss of the MT it will essentially come down to just mods and not the driver. Alas the fun will be gone.

Still all this is has been very informative, thanks for the read.

NmexMAX

iTrader: (22)

Apperently you have never popped open a manual transmission before have you? More gears = more loss.



The more gears there the more energy and work you need to spin the wheels, which results in more parasitic loss.

This is a 5 speed.... Imagine one more gear in there...






This can be seen when comparing the Maxima specifically.

All cases in stock form averages of Dynojet 248 data, which can be found using the search function or the dyno forum.


The A32/33 typically puts out 10-15 more whp than it's automatic brother. (154-157, vs 163-167, or ~ 6 - 8%)

The A33B puts out 5-10 more whp than its automatic counterpart. (194-196 vs 200-204 or ~ 4 - 5%)

Although some of this can be attributed theoretically to the obese FWD VQ35 flywheel, but flywheel gains have yet to be proven definitively on a dyno.

SilverMax_04

Spinning gears are like spinning flywheels, they take some energy to get spinning, but little to keep them spinning. By adding one more set of gears (from 5 to 6 sets) spinning in a manual trannie, I suspect that you can not measure the incremental energy needed to spin that extra gear set. While your point is technically true, it is a great example of "Gilding the Lilly" when it comes to measuring the additional energy loss in a manual trannie from having another gear set = negligible.

And the variability in wheel dino readings do not prove anything except that they are variable.

jcalabria

At...
...our federal gov't (they would never lie, would they? ) indicates that, relative to a conventional automatic, a CVT should realize a 6% improvement in efficiency.

While they don't specifically compare anything to a conventional manual gearbox, they indicate that an Automated Manual Transmission (Audi DSG, BMW SMG, Ferrari F1) would realize a 7% improvement over the conventional slushbox. It would seem to me that a conventional fully manual gearbox would be even better, since it wouldn't have the parasitic losses of the systems that operate the autoclutch and shift-by-wire systems.

For now I will agree with SilverMax_04 that the conventional manual theoretically can be the most efficient. But it wouldn't take much for aggressive (or ham-fisted) driving to throw the theoretical advantage out the window.

SilverMax_04

It depends on the agenda of the agency and/or the people running it.
I'm always suspicious.

Thanks. I think that aggressive driving of any powertrain combo (no matter which trannie is installed) can throw efficiency advantages out the window -- including the CVT. I do acknowledge that there is some improved engine efficiency from operating at the optimum all of the time (provided you do that) with a CVT. What I don't know is whether this improvement is enough to cancel out the loss of energy in extra heat that the CVT produces. My suspicion is that the manual gear box is the overall winner -- but I have no authority to cite (except by extrapolation of the data on the government site you cite).

Manual trannies are also the cheapest to repair should that be necessary. And because they are much simpler mechanically, they don't need repairs as frequently -- provided you are not a ham-fisted driver.

iwanaMAx

the cvt in my galant took a **** on me and has been in the shop for a month already....

Apparition

iTrader: (5)

any mitsubishi trans is FTL.. my mom has an Endeavor and that thing is quick (same engine as your galant I believe), but that tranny is garbage.

iwanaMAx

nah i like the tranny better than my o6 max tranny, but now its in the shop so im stuck driving the max....well its not that bad but i love my G

imported_White_lightning

I have read that with the MAxima CVT there is an issue that when you kick over from CVT to "manual" it wont gointo 6th unless you force it. Has there been a TsB write up about it? or a fix?

jcalabria

I don't know if its an "issue" or a "feature", but mine always goes to 5th or lower when you slide it over to the manual gate.

Remember, chances are it will always have to shift somewhere because it can be at any of a virtually infinite number of ratios and you are asking it to conform to one of 6 fixed ratios.

The shifts are so smooth, even into or between the fixed ratios, that its not really an issue.