How reliable would a CVT transmission be in constant stop and go driving?


#1

My mail carrier drives a relatively new Nissan Juke, the strange bug eyed car. You can see the thing coming from a long way off and it is very distinctive. It is also odd to see a rural mail carrier driving a newish car as they usually have a reliable old beater as it gets lots of hard miles. I decided to look up this car one day and it only comes with a CVT. It is used in many other Nissan products and other car makers such as the Mitsubishi Mirage. Most are Asian and many are not available here. See http://www.jatco.co.jp/ENGLISH/products/cvt/cvt7.html

I am curious how well something like this will hold up to the constant stop and go use of a mail carrier. I suspect fluid changes might be more important in this application. I am sure this is great for the fuel economy but how about long-term reliability?


#2

I can’t predict how reliable this transmission will be in this vehicle, but the beauty of a CVT transmission is that it is made for stop-and-go driving. It is constantly calculating and using the most efficient gear ratio for the conditions. It does the same thing at high constant speeds too, but at constant highway speeds, it doesn’t get much better fuel economy than a regular five speed or six speed transmission.

I used to consider it a weakness of the CVT that it can’t be repaired, only replaced, but anyone who has ever driven a jerky rebuilt automatic transmission would probably prefer a replacement over a repair.

Edit: I just remembered one of our fleet vehicles at work is a 2005 Prius that came with a CVT. As far as I know, the transmission has had no issues.


#3

I think the jury is still out on CVTs. A mail route would certainly be an “acid test”, and while I know it’s unrealistic to expect to find out how it makes out after a few hundred thousand miles, it sure would be interesting.


#4

The jury is still out on the CVT but the reliability of a CVT looks pretty good right now. My wife owned a Nissan Sentra for a couple of years and it performed flawlessly. In fact, the CVT performed above average during the heavy snow conditions during the 2 winters that my wife owned the little car. While many of her neighbors were stuck in their driveways for days…my wife drove around with ease during the times of the heaviest snows. She never got stuck even once.


#5

I also see “NY Taxi” listed as a vehicle equipped with a CVT so I am sure that is also a good test of the technology. http://www.jatco.co.jp/ENGLISH/products/vehicle.html

I understand there are different styles of these things. Some use a belt while some use cones. The CVT in the Juke is the same one as the Mirage which is a belt type attached to a 2 speed automatic transmission for a high and low range.

I remember when they first became popular that they couldn’t handle too much extra torque above stock so people tuning their engines for extra power had issues with them.

As for replacement, I understand that all the parts wear into each other so just replacing some parts during a rebuild would bring about poor results. This is why they are just replaced, not rebuilt. I am sure the cost of this will send many cars to the scrapyard, especially cheaper cars like the Mirage.

I hear these have really come a long way in recent years. I didn’t look at all the various designs made by this manufacturer but see that the Mitsubishi Outlander also uses a model of CVT. This is a pretty large SUV so am sure the design is different for that application.

There are also other makers of these but this one seems to be the common one as you see it in many Nissan cars.


#6

Here’s a primer on CVTs in the American automobile market–not gonna talk about hydrostatic CVTs in agricultural or construction equipment.

The Toyota hybrid synergy drive is essentially an electric torque converter. Power from the combustion engine is sometimes sent to the generator then to a traction motor, which has a lot more torque than the combustion engine. In other situations, more of the power goes through the gears rather than the less efficient electric path. In a nutshell, power is converted to torque just like a hydraulic one. But this one has a battery that supplies power to the wheels. Imagine having a high pressure hydraulic accumulator that can shoot hydraulic fluid at the turbine without the engine running.

The frictional CVT are two large pulleys that clamps a metal belt or chain(more on those later). There are various web sites with diagrams explaining how ratio is changed. The drive capacity is dependent on the friction between the two metal parts(belt and pulleys), much like friction between train wheels and rail. This is why you don’t see OTR trucks hauling fruits to your local grocery stores using CVT. There’s not enough clamping force, or light enough material to withstand the clamping force without much deformation

CVTs use a special elixir that is liquid like at low pressure but turns into a solid substance when clamped between the belt and pulleys. In theory, there should be no contact between the belt, but we all know cars transported by trains are covered with rail dust. There are ASME papers that talks about slippage in a CVT. Just like engines, parts that slide past each other without lubrication wears out eventually. CVTs depends on parts not to slip and slip they do anyways

I know gears slip all the time as teeth mesh, but gears have lubrication that facilitates slippage. CVTs use traction fluid to resist slippage

The choice between belt or chain depends on the manufacturer. Chains can follow around the pulley in a tighter circle, which leads to wider ratio spread However, chains dive in and leave the pulleys at discrete points and this causes vibration.

Back to the OPs question. Because the cvt slips and wears all the time, the more you vary your speed the better since you are spreading the pulley wear across the entire range. If you use CVT in stop and go traffic or highway cruising, you’re subjecting the low or high range to constant wearing.


#7

Well this sounds like the perfect application as a mail carrier vehicle. I wonder if they researched this before buying the vehicle for this purpose.


#8

someone said not to do any Ag comparision ,but I see by the retailers product pages and reviews that a lot of larger yard tractors and lawn mowers are going the cvt route ,I saw A very nice ,fairly new higher end John Deere sitting in the junk lot , at a sewage treatment plant ,Turns out the hydro stat drive unit went out and it was simply too expensive to repair it was cheaper to buy a new equall y as capable much cheaper red riding mower(they wouldnt let me have the twin briggsmotor ,I had a need for that) ever price a short block for a vertical 2 cyl Kawasaki,it will scare you to death.
All in all I think the CVT or even no transmission (electric vehicles) will come of age in autos.


#9

If you paid formula e any attention at all, you’d know that there’s a transmission sitting between the motor and differential. Electric motors can produce max torque at 0rpm, but it’s not efficient to do so. You want to allow the motor to get out of that inefficient low speed range ASAP.

In their current form, electric vehicles have no energy to spare for the hydraulic pumps required in slush box or belt box. Formula e cars use 2 to 5 speeds automated manuals


#10

Sorry dont follow "racing " it seems that there is no transmission between the dynamo and electric motor on a one hundred ton locomotive ,so I would assume that the electric motor is a pretty fair "transmission " itself ,so if the manufacturers are goung to make something that could be as simple and maintenance free as an electric car as complex and expensive to maintain as a ICE powered car ,they can keep them.
The compound hybrids(what I call them anyway) such as the Chevy Volt,make little sense to me ,since I can purchase a bread and butter ICE car for a little over half the price ,even when gas hits $4 a gal again (soon ) it still makes little sense,maybe my direct drive "skil saw " needs a transmission maybe ?(not talking about a worm drive ) no need to junk up something for a few percent gain and manifold increase in complexity(I hate getting the stinking gear oil on me- I think bad thoughts everytime I have to service the excavators and such,(tubes and tubes of stinking expensive grease(Caterpillars cash cow) Because JD already has lube free pivot points and wear joints on some huge construction equipment that will last a couple of thousand hours in Quarry conditions.
Caterpillar has track pins and bushings on their equipment that will last thousands of hours( why not on some of their other wear points ?) Anyway you know where planned obsolescence leads.(thats one reason steel was the perfect material to build cars of )


#11

Trains generally cruise for hours when the motors are not producing peak torque at near 0 rpm. They are also traction limited which means they may not be using peak torque to start. A mechanical transmission adds more weight and complexity for very little efficiency gain.

Cars and formula e are driven in a variety of conditions. They have to navigate the parking lots in los Angeles, slow down for curves then speed up again, cruise across the desert. In many situations, the electric motor in a car would not be operating at its efficient range. This is where a efficient mechanical transmission would help


#12

Something you are forgetting is that electric motors on trains also function as dynamic brakes with the generated current being run through resistance bars to disappate it .(also will work on a truck ) Works good on electric cars also and you can computer control electric motors for best performance a transmission in my opinion is an unecrssary complication ,the huge mining trucks and loaders get by without much in the way of a transmission and they are usually run to the max,back in the day even shovels were rtan on line current and I bet that was a pain to keep the cables out of the way.
One problem with using the smaller motors and transmissions will be the manus temptation to make them light duty and cheap .(plus more nasty petrol based lubes to contend with .) (If I never have to replace a seal again or change the gear lube it wont hurt my feelings at all)
Another thing about the electromotives was that you could start a load better then the wild unbrideled torque of the old steam beasts ,the Diesel electrics werent cheaper ,but the industry thought they were better .But what hurts me is this why cant we have a strategic reserve of these old coal powered freight movers just in case of of catastrophe ?.I think they even decommissioned the last fast coal powered ship (the America ?) it was capable of 40 + knots I believe,however you never know steampunk may rule again after the “zombie apocalypse” already happened in certain areas:wink: