Question for Mark K

[roofeditor]

Transmission engineer or any others with the technical expertise to answer.

I have my Detective H/W friends next door that have a Nissan with the CVT transmission.

Question: How well do they hold up and how efficient are they? They feel odd when driving like you are slipping the clutch?

I've also driven a couple of cars with the Twin clutches. And from what I read it's 2 manual transmissions and 2 manual clutches running side by side when a gear change is needed is simply switches to the next "transmission" which is in gear already. They claim gear changes are in thousands of a second and slippage is zero? They do appear very effective and shifting if slightly firm but delay and slippage appears to be zero. How do they hold up? and what would be the downside?

OK OK that's more than one question.

DSG and twin-clutch transmissions - What the DSG / twin clutch transmission is - how the DSG /twin clutch transmission works

Direct-Shift Gearbox - Wikipedia, the free encyclopedia

Here is a CVT. look at the photo. looks a revved up snow-machine tranny?

CVT - what the Continuously Variable Transmission is and how CVT works

Just looks like it would burn up eventually?

[Mark Kovalsky]

Twin clutch (DSG) transmissions are the trans of the future. That's where the industry is heading. A different division of the company that just laid me off has one in production and another one close behind.

They are like two manual transmissions with two clutches. One clutch is driving one gear and the next one is right at the point of applying. It's much more complicated than an automated manual trans, but they do work well.

VW/Audi has had them in production for several years. I don't know how they do on durability, but I haven't heard any bad news, if that's worth anything.

CVTs came and are leaving. I think there won't be many more in the market place. Ford already dropped theirs after three years of production. They are essentially a revved up snowmobile trans, but how would a Floridian know about snowmobiles?

I owned one in a 2005 Ford Five Hundred. I really liked it, but wife wrapped the car around a tree. It took some getting used to because the engine doesn't rev then drop in RPM at a shift and rev again. It just goes to one RPM, which is around peak torque RPM, and just sits there. The trans ratio changes as the car accelerates to keep the engine producing at peak torque. It's great in theory, but the belt is a problem. Ford/ZF used a metal belt that durability testing showed held up very well.

Efficiency is their strong point, though in the Ford application the same car with a six speed auto got one MPG better fuel economy. I believe that was due to poor programming on the CVT. My CVT left the torque converter unlocked most of the time. I would have kept it locked from shortly after launch and adjusted the trans ratio to compensate. That should help efficiency quite a bit, but it might have compromised smoothness.

The Five Hundred had a 3.0L engine, which I believe was the biggest engine ever offered with a CVT. Nobody has been able to make one work with larger engines. The belts have a very short life with larger engines.

[roofeditor]

I used to live in North North NYS and yes we had snow machines for the woods and lakes.

As the RPM's change the front wheel goes to a higher tighter fit and the rear wheel goes smaller. Still a lot of slipping going on there! Friction? Friction is generally heat and heat is power loss....usually.

The twin clutch is so fast you don't even know it happened.

The older auto/manual that was in the BMW-M-3 was horrible. In one setting it was so jerky you're thinking you are going to snap a drive shaft ot CV joint. In lesser settings the lag was so bad it sucked. I think it was a 5 or 10 grand option.

I drove one of the new VW's and it's pretty cool this DSG.

[fireguywtc]

great post guys! Good question Roofeditor,and awsome info. mark. Very interesting reading and I think it's a really cool idea. Maybe someday it could benefit diesel pickups.

[checkthisout]

For what it's worth.

Honda has been using a CVT in one form or another since 96. Subaru had one out in 85.

In Honda, there is a "clutch" which takes the place of the torque converter. This clutch "slips" to provide "creep" while in gear and of course engages much like you would engage a manual transmission clutch as soon as you press the gas pedal.

This clutch causes a lot of problems because it generates a lot of heat.

I have never seen the belt itself fail. The Civic Hybrid uses a CVT so there are quite a few of them on the road. The new models do not have the problems with the clutch that the older ones did.

The pulleys for the belt are moved in and out by hydraulic pressure and that pressure is of course controlled by the PCM to maintain the proper pressure on the belt to prevent slippage.

A fact you will find interesting is that the belt is "Pushed" by the pulleys instead of being "pulled".




And I agree with Mark,

After driving those Hondas that have to rev to 5000 RPM to go anywhere, I was taken aback the first time I drove a Ford 500 equipped with a CVT. The feel is totally different with a big, hi-torque V6. It's quite rewarding to drive with a feeling akin to powerstroke with a powerchip when you roll into it with the TC locked-up.


I think Nissan has a CVT in the Maxima. That thing is probably a hoot to drive.

[Mark Kovalsky]

Originally Posted by roofeditor

As the RPM's change the front wheel goes to a higher tighter fit and the rear wheel goes smaller. Still a lot of slipping going on there! Friction? Friction is generally heat and heat is power loss....usually.

Heat is ALWAYS power loss.

In this case there isn't much slipping going on. The system was designed to minimize slippage of the belt on the pulleys. That's why it is so critical to have the right fluid in a CVT. It will get destroyed incredibly fast with the wrong fluid.