A CVT for the future...

[AZhitman]

Manufacturers are continuously developing new technologies that will make the production of hybrid vehicles more efficient and cost-effective. Many SEMA members have indicated that the advent of hybrid vehicles has posed a threat to their businesses. However, the companies that develop new products for hybrids may have a competitive advantage in the automotive specialty-equipment market. One company, NexxtDrive, has developed a technology that it believes will facilitate a fast, low-cost integration of a hybrid electric system. The DualDrive system is a continuously variable transmission (CVT) that includes an electric drive capability and will take up less space than a conventional automatic gearbox with torque converter. The DualDrive system will allow manufacturers to use a single transmission for both hybrid and non-hybrid vehicle variants, incorporating an epicyclic geartrain to combine the drive from the vehicle with two electric motor/generators. Under normal conditions, one of the motor/generators will operate as a generator, while the other will function as a motor. Power from the engine is thereby split between a mechanical drive path through the geartrain and an electrical path from the generator to the motor. Speed and torque at the output shaft can be controlled by altering the way in which transmitted power is routed between the electrical and mechanical drive paths. Power is recombined by the epicyclic gearbox and transmitted to the vehicle propshaft. Frank Moeller, director and chief engineer for NexxtDrive, said “A critical advantage of the DualDrive approach compared to those of alternative electrical/mechanical power splitting devices, is that a larger proportion of the power is transferred through the highly efficient mechanical gearbox, while control is achieved using the smaller electrical power path.” He believes that overall system efficiency will be high, with potential fuel and CO2 emissions savings of up to 20%. Another advantage of the DualDrive system is that the electric generator/motors may be able to replace the vehicle’s conventional starter motor and alternator in order to deliver a start-stop function for added fuel savings in city traffic. Furthermore, DualDrive has the potential to eliminate some of the costs associated with the development of a vehicle-specific hybrid transmission solution. NexxtDrive is currently conducting studies with an un-named OEM, and has stated that the DualDrive has been shown to provide automatic transmission capabilities in vehicles where it had been previously impossible to package such a system.

Source: Stuart Birch, “NexxtDrive’s space-saving CVT”, Automotive Engineering International

[JimmyMethod]

But where's the fun in a CVT?

[skylndrftr]

how bout unlimited use of peak torque...plus you could tune an engine with awful characteristics except at one point where it makes 500ft-lb and gets 500 mpg.

honestly I don't know if I would ever buy a vehicle with a 'friction' drive system. its one thing to replace brake pads or a clutch but consider having to buy a new/rebuild a gearbox like a clutch.

[InsanityInc]

I don't get why people think hybrids are so awesome. Put a small, efficient diesel in a car the size of a hybrid and your gas milage will be just as good, if not better, and it will actually drive like a car, instead of a lump of crap.

Hell, most K-Cars get over 40mpg, and they use gasoline engines.

[DrewQ45]

I don't get why people think hybrids are so awesome. Put a small, efficient diesel in a car the size of a hybrid and your gas milage will be just as good, if not better, and it will actually drive like a car, instead of a lump of crap.

Hell, most K-Cars get over 40mpg, and they use gasoline engines.

Hybrid makers are finding that their cars are faster off the line due to the electrical motors assisting. You save gas and get better performance, less emissions, not to mention that the technology is still young and improving.

...Drew...

[maxnix]

Hybrid makers are finding that their cars are faster off the line due to the electrical motors assisting. You save gas and get better performance, less emissions, not to mention that the technology is still young and improving.

...Drew...

Yeah, but htese advantages evaporate with long highway trips at speed. A couple of passes at high speed, and your batteries are drained, and you are left with your base gasoline engines power. The new GS450h is fast off the line tahnks to its electric motors, but its top speed is only 130mph due to its small engine.

Hybrids are OK for short urban trips, lousy for high speed interstates and highways.

[C-Kwik]

Yeah, but these advantages evaporate with long highway trips at speed. A couple of passes at high speed, and your batteries are drained, and you are left with your base gasoline engines power. The new GS450h is fast off the line tahnks to its electric motors, but its top speed is only 130mph due to its small engine.

Hybrids are OK for short urban trips, lousy for high speed interstates and highways.

This is exactly the point. A large percentage of people spend most of their wheel time sitting in bumper to bumper traffic everyday. Not on long trips with light traffic. Regenerative braking recovers some of the energy that would otherwise be lost each time you hit the brakes. It offers big advantages over small displacement motors or even diesels. There are of course those that do make long fast trips. Each person should choose their car based on their own needs. And even then, there will likely be some level of compromise. No car is that perfect.

[Mettler]

CVTs are crap, weak gearboxes that couldn't actually handle the type of power you guys are talking about.

Hybrid cars are crap, and I've seen an episode of top gear where they reviewed some toyota hybrid, which turned out to have worse fuel consumption than an equivalent model diesel... looked like arse, and still cost more to buy.

[skylndrftr]

but you get large tax breaks (for a little while longer at least) with the hybrids.

*You also can get them with large SUV's by using then for 'business' which can include commuting in it

[AZhitman]

I'll concur that hybrids are a joke, and could go on and on about why.

However, I gotta disagree on the CVT = weak issue. Some of the newer designs are perfectly capable of handling high-hp applications (remember, they're not the early "belt-drive CVT's anymore).

[Nyloc]

have you seen this concept AZhitman ?The videos are a bit cheesy, but the concept in action is pretty mind blowing.

http://www.torotrak.com/IVT/

[AZhitman]

VERY impressive!

I had seen somethnig about this in Popular Mechanics a while back... The possibilities are pretty amazing.

[JedCoop]

have you seen this concept AZhitman ?The videos are a bit cheesy, but the concept in action is pretty mind blowing.

http://www.torotrak.com/IVT/

Two aspects to the design: general geometry - pretty complicated stuff, and this is a nice way to make it compact.

But it is the traction fluid that makes it possible. I have not looked at CVTs in many years, but it remains that contact point geometry is very difficult. The videos show a wheel with squarish edges contacting a disk, and a patch of "traction fluid" that interlocks at the molecular level under high pressure.

Contact between surfaces of equal hardness usually means massive wear. In this case I'd assume that the disk and wheels are of equal hardness, and the "traction fluid" acts as the wearing surface. It will break down. I just have no idea how that really works in wide temperature swings, or at low versus high speeds. Also how to shape the wheel so that the contact patch is predictable and does not continuously twist against the disk.

Just thinking out loud really. This is a hard problem, and as I said I haven't looked at it in years. (I am a Mechanical Engr. that does software now).

I like the idea of putting this into a 4wd vehicle. With small size you could have one of these inboard on each half shaft.... kind of a combined differential/transmission for each wheel to reduce the torque each needs to handle. More relible too? (if one CVT fails, the car still goes).

[JedCoop]

Just for fun I looked up patents for "traction fluid"Not too many. A few in the early '90s from one company in Japan.Except for one patent from Lubrizoil corp, all the rest are from GM!

Traction fluids are generally esters - vegtable oil and brake fluid are examples of low and high viscosity esters.

This patent has a nice explanation of what is going on if you are interested.

http://patft1.uspto.gov/netacg...7,680Read the background section.

[kerrton]

CVTs are crap, weak gearboxes that couldn't actually handle the type of power you guys are talking about.

Hybrid cars are crap, and I've seen an episode of top gear where they reviewed some toyota hybrid, which turned out to have worse fuel consumption than an equivalent model diesel... looked like arse, and still cost more to buy.

Well I don't know, the current CVT's have vastly improved reliability and durability, and talk about handling power,the current Murano exlusively uses the CVT (as always) and the 3.5 L generates 265 hp and 248 torque which is pretty impressive. For comparision, I think the original Pathfinder 3.0 L which was considered a rugged machine only generated around 150 horsepower, so even our opinions about what constitutes "a lot of power" have really changed with newer engine and trans technology.


Another interesting thought regarding the trucks, the 4.0 L engine used in the Xterra, Pathfinder and Frontier numbers are very similar to the Murano 266hp and around 280 lb ft torque. How much further could the CVT be pushed, would it stand up to the 4.0 L power? Probably the better question is would it stand up to what truck owners would likely throw at it? But people with Murano's tow small trailers etc. to around the 3500 lb limit with the CVT, so maybe it's not used in the trucks because of buyer perceptions more than real physical limitation?

[JimmyMethod]

The concept of a CVT could be good. Ideally it works like a variable pitch blade on a propeller. The engine can always run at the ideal RPM and the transmission will adjust how fast the car goes given that RPM based on the drivers needs.
However, I must say: No fun.

[elwesso]

actually i was in an altima one time with the CVT. My buddy rented one time and also has a golf GTI with the SMG gearbox or whatever they call it..

Anyway, the altima had a 6 speed "sport shift" option, and it shifted quicker and smoother than the GTI did.. So saying a CVT is no fun might not be entirely true...

[numbnuts240]

i HATE how my mother's lancer drives. i keep waiting for the shift that never comes. paddle shifters are a stupid gimmick in economy cars, and the tiptronic is just as lame. plus i kept stomping the empty space where there is no clutch pedal when i went to start it.

[s0m3th1ngAZ]

I've driven a mini cooper with the CVT...weak sauce. Sounds like the engine is dying going up a hill.

[Jesda]

CVTs are fine except the flaky pieces of garbage Nissan sells.

The average everyman barely remembers to change his oil, much less cares about driving enjoyment.

[Looneybomber]

I'm still holding firm to the idea of electrically driven cars powered by a generator and turbine. No need for transmission, just a gearbox for the gear reduction.

[kerrton]

Well I don't think you can really comment on the Nissan CVT unless you drive a recent model. I own the Rogue, and while it isn't perfect I really appreciate it because of the amazing fuel efficiency I get out of it, especially around town ( I get the rated 31 miles/imperial gallon, or 7 liters/100km) which is better than many mid-size cars, and the Rogue is quick roomy, exterior size is roughly that of the old Pathfinders. On the highway, it's really nice when you hit hills, instead of the transmission dropping suddenly down a gear and revving like crazy, the CVT makes a minor adjustment, or the bare min. lowering in gear ratio and you don't even notice a very slight increase in rpms.

Referring to the collosal disaster that was the mini cooper CVT is not a fair comparison, it was a crap design and is not relevant in a Nissan discussion. And the Nissan/Jatco CVT has been drastically improved since it was introduced in 2003.

Anyway, they have CVT is the only transmission available in the Murano 3.5 L engine which makes around 230 hp, so to say the CVT is not durable is inaccurate, and if you get your hands on reliability stats the transmission is always rated well above average meaning it outperforms conventional transmission's. Most of what you guys are saying is based on the fact that you're used to the driving feel of a conventional or manual shift, I found it took me a few weeks to get used to it now I think conventional autos are crap with all the jolting and jolting noises.

[Jesda]

Gauging reliability on a newer CVT isn't a very accurate science. Once more sample data is available you can reach a stronger conclusion.

As for the CVT-powered cars currently on the road since the turn of the century, they are to be avoided.

[kerrton]

Ok, I'll follow your point about lack of sample size to base a positive conclusion about CVT reliability, but where do you get the data that supports the statement "CVT's are to be avoided"?? That is based purely on your perception and no real data - you can't have it both ways, if you critisize me data then you'd better have a good solid source to back up your conclusions! I have access to reports of hundreds of high mileage CVT vehicles over the 300,000 mile mark and they are still running smooth as new, unlike conventionals that degrade over time and shift points can get very rough, if you're lucky enough to even make it close to 300k. And to back up Nissan's confidence in the technology, they now offer 10 year, 200,000 mile warranties for all new AND existing CVT vehicles retroactively. That in itself should settle any disputes over quality, Nissan would go out of business if their CVT was crap and now comes with that amazing warranty that no other manufacturer even comes close to matching except Mitsubishi.

I agree a larger sample size is prefereable, but I think the sample size for the CVT is sufficient to draw some conclusions that are well within in my tolerable confidence interval. The most basic fact that Nissan has fully adopted these transmission in all but their large trucks, and have been successfully deploying these for almost a decade now, should be enough assurance for most people. For those who are a little more detail orientated and dilligent, you will find a large sample of several hundred thousand vehicles per year, for lets say the last 5 years including North America, Europe and Japan along with some smaller markets. Based on this sample size, all of the major consumer reports organizations such as Edmonds, Consumer Reports, JD Power and others consistently report Nissan reliability as above average, and those that I've seen that break out each component have reported transmissions are excellent or way above average. Did you know that the No. 1 selling vehicle in Europe in any class is the Nissan Dualis/Rogue?

The interesting thing is that human perceptions are always the issue rather than reality. If you drive a Ford, GM, or Chrysler Dodge you will notice that your dealership employs a minimum of one full time tranmission tech/mechanic. He does nothing but work on transmissions, some old and some new under warranty. For those with transmission problems on new cars (warranty claims) I am sure nobody says "this conventional transmission design sucks, it's weak and I've got proof, look at my new transmission! I'll never buy a conventional auto trans again!" Of course nobody ever says that, but if the same situation happens to an owner of a CVT, they are much more likely to say "CVT's suck, they're not reliable and I'll never buy one again". But of course this isn't a fair, and people are biased towards things that are relatively new compared to old "tried and true" technology.

I'm not saying conventional autos are crap, but they have their share of problems and the complexity and cost to repair is a real issue. CVT's have an advantage in their relative simplicity of design, FAR less parts, cheaper to produce which is why Nissan replaces defective CVT's rather than trying to rebuild them, it's a quick 3 hour job roughly and you're on your way. These are still very expensive because they haven't reached economies of scale but cost is coming down rapidly.

[Koshin]

CVT = teh ghey

dont like them...unfotunately, the days of the good old 5-speed gearbox are gone

...makes me sad

[kerrton]

On the topic of driving experienc, I agree, I'd take a 5 speed over a CVT or conventional auto any day too. And also the 5 speed should have the best reliability and/or affordable repairs.

[Jesda]

The interesting thing is that human perceptions are always the issue rather than reality. If you drive a Ford, GM, or Chrysler Dodge you will notice that your dealership employs a minimum of one full time tranmission tech/mechanic. He does nothing but work on transmissions, some old and some new under warranty. For those with transmission problems on new cars (warranty claims) I am sure nobody says "this conventional transmission design sucks, it's weak and I've got proof, look at my new transmission! I'll never buy a conventional auto trans again!" Of course nobody ever says that, but if the same situation happens to an owner of a CVT, they are much more likely to say "CVT's suck, they're not reliable and I'll never buy one again". But of course this isn't a fair, and people are biased towards things that are relatively new compared to old "tried and true" technology.

To effectively gauge reliability, you need a 3-year VDS. It hasnt been three years yet.

You already agree that the old ones were trash, so why refute? Your claim is that the new ones aren't. You may be entirely right, but I would NOT tell someone to jump on a bandwagon that doesn't have widespread acceptance and valid skepticism, especially if the consequence is several thousands of dollars out of their pocket. When you suggest a used vehicle to someone, you have a responsibility, and historical concerns should be placed above future hopes. New is a different matter, since the warranty on most new cars is likely to offer reasonable powertrain coverage.

In a year, if the rate of problems has declined, then we can effectively say its ready for prime time. For now, I tell anyone who asks about a late-model used car to avoid CVT because it isn't yet proven. It may BE okay, but two years is NOT long enough to determine if it will be over the long term. By three years (30-50k), most cars have shaken out their defects. We'll know by then if anything was defective.

[kerrton]

I agree that it is a resonsibility to carefully consider advice that we give, but like I said in my second last message, the "new" significantly redesigned models have been out since 2005, and if you go with your 3-year rule, they've definatley been out since 2007. And like I said, in addition to the 3-year rule, Nissan also has extremely high volume because the CVT isn't used in just one or two vehicles, it's used in every vehicle in their lineup except the trucks, AND they have large market shares in Europe and Japan where the CVT has been used for almost a decade. They wouldn't adopt this as their primary transmission if they hadn't done years and years of grueling tests to really push the limits of the technology - who knows when they started testing but for them to completely adopt the technology I'm sure it was at least a decade ago that they started seriously testing it and I'm sure it's been around for a couple decades in the "tinkering" stage. After all these extreme tests Nissan felt confident to adopt it in all cars and that instills confidence that my relatively easy driving shouldn't cause any issues with my CVT.

But of course the more years of record the better.