CVT 3

[Esjay]

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?

 

[RCDude]

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.

 

[crysta1c1ear]

I've read on the

http://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!

 

[drwebb]

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

 

[carnage1]

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

 

[shanba]

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%.

 

[drwebb]

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.

 

[GraviMan]

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

 

[crysta1c1ear]

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.

 

[JayMaechtlen]

"...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

 

[GregLocock]

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

 

[crysta1c1ear]

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.

 

[drwebb]

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.

 

[crysta1c1ear]

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.

 

[GraviMan]

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

 

[808state]

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.

 

[808state]

Ive found another CVT that may or may not be helpful to me.

http://cvt.com.sapo.pt/MCVT/MCVT.htm

Hoorah Grease Monkey