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CVT

CVT

(OP)
I`m considering purchasing a Nissan Murano w/ a continuously variable transmission. I realize that cvt technology is as old as the light bulb, but most automotive applications until recently have been w/ fairly low horsepower applications. What should the consumer expect in the way of long-term reliability from the Murano cvt, which is hooked up to a fairly potent 3.5 liter V6?

RE: CVT

You should expect to be part of a long-term "proof" that the design works as well as "intended".  Being a gambler might help, except I don't see a jackpot as a possible win.

What is wrong with the usual trans?  And, having owned Nissans, Toyotas and Hondas, my opinion is that Toy. and Hon. are well ahead of Nis. in engr., etc.

RE: CVT

(OP)
Honda and Toyota are using CVTs, notably in the Civic Hybrid, Toyota Prius. They are smoother, of course, and maybe more efficient in some cases. The Nissan CVT is made by JATCO, not exactly something Nissan came up with on its own.

RE: CVT

Honda's CVT's have been on the market for about six years, using a metal belt that transmits power via compression as opposed to tension used in v-belts.  The horsepower limit for this belt design is around 100 hp which is why it has only been seen in Civic sized vehicles.  VW Audi's design uses belts under tension that are driven off the pins that join the links of the belt together.  These CVTs are rated at up to 300 hp.  I'm not sure what type the Nissan has.  I've had a Honda Civic HX CVT for fours years and its been very reliable, but you must take care to adhere to the manaufacturer's requirements about changing the transission lubricant at the required intervals.

RE: CVT

how much does the extended warranty cost?
Get coverage for somewhat longer than you intend to have the car!

Jay Maechtlen

RE: CVT

We have plenty of subaru Justys in the area (3 in our yard!) and the metal belt CVT worked great in them for 100 000 km usually.  There is a metal problem and the sheeve wears when highway driven at the same speed.  We grab them for parts for our 5 spd!

We do own one working one which we are driving and it is a really neat thing to drive! Much nicer than a normal auto!

Ken

RE: CVT

lives only 100k km?

I expect a conventional automatic to do much better than 100k miles!

it's funny- at low speeds, a conventional (lazy american) automatic looks a bit like a cvt, due to the torque converter. Cruise in town, maybe turn 1500-1800 rpm.
Gas it a bit, goes to 2500-3000 immediately, without downshift!
(Buick Regal, 3.8, 4-speed auto.)


Jay Maechtlen

RE: CVT

(OP)
He said 100,000 kilometers, which is more like 60,000 miles.
surely they last longer than that!

RE: CVT

The Murano is not a belt-and-sheave CVT, but a toroidal CVT.  Again, it's not a new idea, but it is a new product and quite different from any OEM's expertise base, so its long-term reliability is risky.

RE: CVT

I know it was 100k KM that was mentioned- I used 100k miles for contrast, to indicate how far from my expectations that figure was.
60k miles is about half what I expect as a reasonable minimum lifetime.
regards

Jay Maechtlen

RE: CVT

Check the Nissan Website:

"Xtronic CVT transfers power through two variable pulleys and a high-strength steel belt."

RE: CVT

Oops.  You're right, drwebb.  The Xtroid (toroidal CVT) is used in the Nissan Cedric, not the Murano.  The Murano CVT is a "traditional" belt-and-sheave system.  They're putting 350N-m through a 30mm wide belt, which is quite a bit more torque than anybody's been daring enough to try in the past.  Apparently, they think that recent process improvements and design changes in the changes allow it.

RE: CVT

Hadn't heard of the Cedric.  It's curious design choices because I haven't heard the same capacity concerns about toroidals as belts and chains. At least Toro-Trak chose a SUV as their demo platform at the 2003 SAE Congress.  Maybe TT knows something Nissan doesn't- or vice'-versa!

RE: CVT

2


Jatco's CVT strategy is quite simple. Half toroidal IVT for RWD and belt drive CVT for FWD.

Belt drive CVTs are currently limited to about 500 Nm, see http://www.luk.de/english/Bibliothek/Download/k7/luk_k7_chap07.pdf
so they would be not useful for anything like a 2000 horsepower 2025 Nm Walley Larson Groundfighter, but should be fine for a housewife driving kids from school to the supermarket in her SUV.

RE: CVT

(OP)
The Murano CVT also offers all wheel drive.
My usual confidence in Nissan tells me that surely they tested this thing in the desert under load. After all, wouldn`t heat be the biggest concern for the belt/

RE: CVT

The challenge is maintaining friction at the belt/pulley steel/steel interface while also maintaining wear control.  I agree that Nissan must be confident the trannies will last through their warranty periods with recommended periodic maintenance without unacceptable failure rates.  Anyone putting anything but the Nissan-recommended ATF in there would be asking for trouble.

I keep meaning to go test-drive one of these when I have the patience to endure the sales pitch.  They seem to be selling well in my area.  Anyone have any driving impressions of this powertrain?  Nissan reportedly wasn't planning to promote the CVT feature of the Murano, so I wonder if it's evident to the driver or not.  Some CVTs even have shift-points synthezized in their ECUs to give the customer what they're expecting- !!

RE: CVT

Hey, gvc99, you mention to adhere to manufacturer's requirements about changing the transmission lubricant. Do you have a Nissan Murano and/or do you know what drain interval Nissan is requiring? It seems the fluid is special. Do they want or expect you to change an expensive fluid often?

RE: CVT

I am from Sri Lanka, using a Honda HRV (smaller version of CRV, VTEC 1600cc, 125 BHP) with CVT.  The meter reads 50,000 km.  

The transmission generates a shudder when starting off from a standstill when the engine is relatively cool.  This disappears when the vehicle is driven for about 15 minutes.  Fluid change eliminated the problem, but the shudder is back after 2,000 km.  I am using Honda Transmission fluid.  Is there a special CVT fluid (which is not available with the local distributer) which I should have used?  Can someone help?

RE: CVT

The justy cvt uses regular dextron atf.  I should mention the odometer does not have a 6th digit which would suggest a 100,000 km expected life span?

We had 330,000 km on our manual transmission model before it threw a rod so that is our comparison to the CVT model.

Ken

RE: CVT

CVT Transmission Fluid:

There is definitly no general CVT- Fluid like an AT-Fluid out there. Every make and eaven model has their own fluid.

I hardly recommend if you think about flushing:
1) Do it in yours contractors shop
2) Use only this one from the OEM recommended.


Berblinger

RE: CVT

I've been shopping the Murano recently.  My driving impression is pretty good - stiff and responsive for an SUV, comparable to a sporty car but not quite like a real sports car.  As for the CVT, it was so smooth that it's hard to get a good sensation of your acceleration.  There's no engine revving or shift that would normally contribute to the impression.

They showed me under the hood - you don't do anything at all with the transmission fluid.  The access tube where the dipstick would go is semi-sealed, you're not even intended to check it.  I read another place the fluid has rubber molecules that help the belt plates and pulleys grab together.

Let the dealer change the fluid and if it shows any problems, only keep it as long as the warranty covers it.  That's MHO.

RE: CVT

I've read on the www.mini2.com forum that BMW shipped some minis with ATF fluid instead of a specific fluid for CVTs. If I remember right, the vehicles were recalled to have the fluid changed. One of the owners subsequently still had problems with the CVT and people on the forum thought the transmission might have been permanently damaged between being factory shipped with the wrong fluid and the fluid being changed.

There were also questions raised about improving the performance of the mini by replacing the air filter with a performance air filter, or other more drastic modifications. I think the official BMW/ZF position is that the engine and CVT are pretty much a matched pair and are nicht-zu-finger-poken!

RE: CVT

Yes, the 20+ HP gain from 'upgrading' the air filter () would definately overpower the CVT!

RE: CVT

anyone know horespower losses on average of a cvt compared to a traditional automatic?

RE: CVT

CVT's have more losses than AT's, but the engine operates in a more efficient range, so the net is an overall improvement of roughly 5-7%.

RE: CVT

For your review RCDude you get a star.  From the Yahoo Autos Website:  "The best way to describe the oil is that it contains "rubber molecules" that provides the grip between the belt and the pulleys."  To a layman perhaps, but this is an engineering forum where the best way to describe it is an elastohydronamic film providing the grip between the belt and the pulleys.  Indeed, there are "rubber molecules" in the oil but they function as viscosity index improvers and DO NOT measureably effect steel on steel friction as Yahoo suggests.

Inefficiency in conventional AT setups is concentrated in the torque converter.  The Murano CVT employs a TC for low speed operation.  Nevertheless, Nissan has claimed the setup adds approximately 2 mpg to the vehicle's (modest) 20/25 mpg efficiency.  Many preproduction CVT designs use wet start clutches instead to improve their efficiency.  Such designs are reported to rival manual transmissions in fuel economy.

RE: CVT

Equally common now is a lockup clutch, designed to lock up the torque converter (input to output) once 1:1 ratio is achieved. Again very high efficiency results - kinda makes you wonder why we have manuals...

Mart

RE: CVT

SUZUKI FINGERPRINT CHECKING STARTER BUTTON



FORD



VOLKSWAGEN



HONDA




DAIMLER



PEUGEOT



HYUNDAI



... kinda makes you wonder why we have manuals ...

The distinction between manuals and automatics is eroded away by drive-by-wire. To refer to a transmission as one or the other is becoming a sign that its an old car.

RE: CVT

"...why we still have manuals?"
The cost difference is what?
From what I've seen, the manual is still a lot cheaper than an automatic!
I suspect that a good CVT may get similar economy to a manual with mediocre driver, though.

Jay Maechtlen

RE: CVT

well, a very good cvt should be able to beat a normally driven manual, quite easily.

Reason is that it can hold the optimum speed for a given demand power, as a continuous function.

I'll pick my favourite example - Toyota Prius. During the standard fuel consumption cycle you'd have to be changing gear every second or so to get close to what it manages, even without a battery.

Cheers

Greg Locock

RE: CVT

carnage1 (Electrical) Feb 27, 2004
anyone know horespower losses on average of a cvt compared to a traditional automatic?



BMW Mini CVT.
http://www.honestjohn.co.uk/road_tests?id=46

PERFORMANCE, FUEL CONSUMPTION
AND CO2 EMISSIONS
MINI One: 1,598cc manual: 0-60: 10.6 seconds; top speed: 115mph; combined mpg 43.5; CO2 emissions 158g/km; Emissions Class EU4; Insurance Group 5

MINI One: 1,598cc CVT auto: 0-60: 12.4 seconds; top speed: 106mph; combined mpg 36.7; CO2 emissions 187g/km; Emissions Class EU4; Insurance Group 5

===============================

115/106=1.08490566037735849056603773584906
1.17702029191883232467070131719473

(Or using the mini cooper figures)
125/115=1.08695652173913043478260869565217
1.1814744801512287334593572778828

Wind resistance governing top speed is a square law, so I've squared the top speed effects to determine the percentage horsepower losses resulting from having a CVT.

==================

The CVT doesn't add 2 seconds to the acceleration time.
The CVT doesn't knock 10 mph off the top speed.
The CVT doesn't knock 7 mpg off the fuel economy.
And the CVT doesn't add 30g/Km to the CO2 emmissions.

But nearly!

===========

Your question was how things compare to an automatic, but a manual might as well be the benchmark for everything nowadays. Automated manuals should have similar efficiency to manuals and are effectively automatic. Drive-by-wire makes the manual/automatic distinction meaningless.

I'd be glad to look at the figures for a better CVT if anybody has a weblink.

RE: CVT

Can someone confirm or refute whether the Mini CVT has 'synthetic' shift points?  As mentioned, an efficiency gain is to be had from allowing the motor to rev to it's efficiency band and let the CVT control the speed adjustment.  But this gives a strange driving experience. (Might stress the tranny, too). I'm not a marketing guy, but I guess the expectaction of the driving experience is very different between Mini- and Prius shoppers.

Perhaps the manual/automatic distinction still has meaning in terms of the clutch operation rather than gear selection.

RE: CVT

Confirm.
Here is more than enough text to answer your question, but there is plenty more on the website if your interested.

http://www.mini2.com/forum/showthread.php?t=41926

When you get a CVT MC you have three transmission selection options. (It is recommended that your MINI be past its brake in mileage (1,250 miles or 2,000 km) before trying this because it is very easy to exceed the maximum recommend engine rpm of 4,500 or 95 mph or 150km/hr.)

“D” This is the fuel economy / normal driving mode. Hold the gas pedal at any position less than the detent (hard spot - feel for it when you drive) and *with an eye on the road* watch the tachometer. It will stay at a fairly constant rpm while the MINI gains speed; never "shifting" in the conventional sense. Stomp the pedal down to the floor and the CVT will run up to the peak 6,000 rpm and then "shift" down, and run the rpm up to 6,000 again as the car accelerates, (until you draw the attention of the police and have to stop.) The CVT will do this as long as the pedal is held to or near the floor (past the detent).

“SD” This is the sport drive mode. The engine rpm will be approximately 800 rpm higher than D mode. To get there, move the shift lever to the right from D mode. The CVT behavior will be similar to D mode. There will be more engine braking in SD mode. It may be used it like a passing gear. Put it into SD when preparing to pass another vehicle to increase the engine rpm toward maximum power.

“+/-” This is manual shifting mode. From SD move the shift lever forward two times and 1 will be displayed in the speedometer where D or SD were. Step on the gas and when you want to "shift", tap the shifter back one time for each "gear". Here's the tricky part: keep your foot on the gas. Do not lift off like a conventional stick shift. If you do, you could find yourself nominated for the dork of the week award. You will have 6 "gears" to choose from in +/- mode. The engine management computer will not let you select a gear and engine rpm combination that is likely to damage the vehicle. e.g., you cannot shift into 6th gear at 25 mph or into 1 at 50 mph. It will also automatically "downshift" if you slow too much and upshift if the rpms go too high. You can downshift just like a stick, but without need for your foot on the gas and clutch work. Also, whilst in a higher gear such as 5 in +/- mode, if the car is going slow enough, pressing the accelerator past the detent will cause the CVT to shift to a lower gear. If you were on a long downhill grade, you could put the CVT into +/- and choose a lower gear for engine braking.

Here's something to experiment with. Put the CVT into 1 (steptronic) and just leave it there as you accelerate. The MINI is programmed to protect itself from "inappropriate" CVT and engine RPM combinations. So if you leave it in 1, it will go to redline and shift itself to 2, 3, etc. You can get similar results keeping the gas pedal floored, but doing this in +/- mode works in less than full throttle positions too.

Even in SD mode, if you let up on the gas, the CVT will go to higher gear ratios. But maybe you don't want it to go to higher ratios... If you use the +/- mode, it will not up-shift when you lift off the gas. It keeps the RPM up and everything running in the power band. You only need to downshift manually to keep the RPM up as you slow. Seems like this would be the best mode for racing with a CVT.

RE: CVT

Why-O-why was such a great system not mated to a nice K-series or Ricardo developed common rail diesel? Will the wonders of the BMW decision making process never cease...

Mart

RE: CVT

There is alot more information on CVT's in japan where they are are being used More and more
lately.
http://www.lasercannon.com/cvt.htm
Im heading up there for my next duty station.
If any one could help me find out the who what wheres of a CVT that can withdstand high rpms and torque (besides the Audi model), it would be much appreciated.

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