CVT Transmission Discussion

[rockhopjohn]

Since this is a pretty new concept for most Subaru drivers I figured I would start up a discussion about it. Hopefully people who have the CVT can post their impressions.

I was interested in how it interacts with the AWD system, and with a little digging over at Cars101.com, I found that it looks like the CVT will operate with the same 90/10 front/rear torque split we have seen in the 4EAT 4-speed auto all these years.

My personal expectation is that the CVT combined with might-as-well-be-a-front-wheel-drive feel of the 90/10 torque split will lead to the least inspiring driving experience we have ever seen in and Outback, even worse than the 4EAT. But that is pure speculation, so I would love to hear some real world experiences, especially from those who have spent some time with the 4EAT.

[number 41]

It's generally agreed the 4EAT with 4.44 axle ratio's, it's low first gear and the doubling of the overall ratio due to the torque converter has, over the years, resulted in a very good combination for off road. I've noticed the 2010 CVT has an axle ration of 3.90. So what is the equivalent of the first gear ratio? And the resulting overal ratio of the new combination?

[rockhopjohn]

3.90:1 is the final drive ratio, I am not sure what the lowest ratio the CVT can produce will be. I agree that that 4EAT was the best option for offroading, and imagine that the CVT will do relatively well for offroading too. But I think the CVT will be pretty uninspiring for spirited driving on the road.

Here are the ratios for the various transmissions. The first number is the ratio within the transmission (how many times the engine turns for on revolution of the output shaft on the tranny). The second number takes into account the gear ration of the differentials (the final drive number listed at the bottom) and give you the final drive ratio for each gear (how many times the engine has to turn for a single rotation of a wheel).

5MT in NA Outbacks:

1- 3.454 --> 14.20
2- 2.062 --> 8.48
3- 1.448 --> 5.95
4- 1.088 --> 4.47
5- 0.825 --> 3.69
final 4.111

5MT in XT (turbo) Outbacks:

1- 3.166 --> 14.07
2- 1.882 --> 8.36
3- 1.296 --> 5.76
4- 0.972 --> 4.32
5- 0.738 --> 3.19
final 4.444

4EAT (NA H4 and 2nd gen H6):

1- 2.785 --> 12.38
2- 1.545 --> 6.87
3- 1.000 --> 4.44
4- 0.694 --> 3.08
final 4.444

5EAT (XT and H6):

1- 3.540 --> 11.58
2- 2.264 --> 7.41
3- 1.471 --> 4.81
4- 1.000 --> 3.27
5- 0.834 --> 2.73
final 3.272

So in fact we can see that the both the Automatics have fairly tall first gear ratios. But are aided by the torque converter, to develop a lot more torque, which helps for offroading. The CVT will not have this benefit, and without knowing its minimum and maximum ratio, we can't calculate the range of final ratios and compare it with the other transmissions.

[NorthernSweden]

Here in Sweden we get the JDM cars and have never had a 90-10 torque split. It is 60-40 for 4EAT here and it is really useful in the snow.

On our manual we get low-range gears for all but specB and diesel versions.

I really hope the CVT does as well in snow and mud as 4EAT and that we get to keep 60-40 split, or more fun 40-60 split. The 5EAT is 45-55 split and that is really great.

More information about the AWD system working with CVT would be great reading!

[mrk610]

Im just wondering if the cvt's turn as high of rpm as the 4eat's did at highway speed. Meaning the 70-75 mph area.

[bhayden]

I didn't realize they'd done away with the torque converter with the CVT. One nice thing about a torque converter is it does easy shock on the drive train when doing things like trailer towing. And speaking of severe duty like trailer towing, if the CVT isn't up to the power of the H6 or the turbo doesn't that make you wonder if the CVT is a bit marginal for the application?

Without a torque converter what gives when the car is "in gear" and you're stopped?

The Subaru design uses a chain but near as I can tell it really functions more like a belt in that it rides on tapered pulleys rather than sprocket arrangement. I'd be concerned with the wear pattern. Wouldn't long amounts of time at one speed (e.g. freeway driving) tend to put a groove in the pulley halves?

Do these babies use ATF or a manual gear lube?

Are they still using the Active Drive AWD system? If so is the section in the tail shaft basically the same as the conventional automatics?

How do they back up? Is that a fixed gear or is this thing capable of 70mph in reverse

[rockhopjohn]

Originally posted by bhayden
I didn't realize they'd done away with the torque converter with the CVT. One nice thing about a torque converter is it does easy shock on the drive train when doing things like trailer towing. And speaking of severe duty like trailer towing, if the CVT isn't up to the power of the H6 or the turbo doesn't that make you wonder if the CVT is a bit marginal for the application?

Without a torque converter what gives when the car is "in gear" and you're stopped?

The Subaru design uses a chain but near as I can tell it really functions more like a belt in that it rides on tapered pulleys rather than sprocket arrangement. I'd be concerned with the wear pattern. Wouldn't long amounts of time at one speed (e.g. freeway driving) tend to put a groove in the pulley halves?

Do these babies use ATF or a manual gear lube?

Are they still using the Active Drive AWD system? If so is the section in the tail shaft basically the same as the conventional automatics?

How do they back up? Is that a fixed gear or is this thing capable of 70mph in reverse

I am not sure they have done away with the torque converter. Maybe they haven't, I haven't seen anything to indicate one way of the other.

I don't know what kind of lube the tranny uses, but Subaru indicates it is a lifetime fluid for the average driver, but recommend replacement at 24,588 miles (what an odd number) for those who haul heavy loads, or tow. So, my assumption is that it is a fluid which is heat sensitive, which makes me think ATF.

The CVT will have the same basic AWD system the 4-speed auto does, with a 90/10 split that varies up to a 50/50 as need. I believe this uses a clutch pack at the rear of the transmission that engages and disengages the clutches as needed.

Don't know what to tell you on the reverse.

[bhayden]

Trying to read up on the Lineartronic and CVTs in general I was at first lead to believe that like many CVT types Subaru had done away with the torque converter. But that looks to be not true.

http://www.drive.subaru.com/Sum09/Sum09_whatmakes.htm

The diagram clearly points to a torque converter. So I'm assuming that there is still some sort of torque multiplication factor.

I'm going to make the assumption that the Nissan CVT is similar in design; although I believe they call the Nissan a 2 spd CVT. I drove a 2009 Altima with the CVT and really didn't like it. They seem to have a "spooling up" behavior where there's a lag while the engine revs up but there is no perceptible acceleration. I'm not sure what causes this; if it's hydraulic or mechanical.

I believe the Active Drive clutches rely on the transmission fluid so if the CVT uses that same system it would be another hint that the CVT uses AFT fluid.

Chains on sprockets, belts in pulleys or belts on a flat drum all make sense to me. A chain on a vee pulley just seems wrong. A couple of things concern me. First there's no tensioner and as the chain stretches the synchronization between the two variable diameter pulleys is going to have to recalibrate to avoid slipping. Side loading the chain (compression) makes it more difficult to go around a bend and follow the pulley. The whole idea seems opposite of what Subaru has been trying to do in reducing friction.

[nipper]

Originally posted by bhayden
Chains on sprockets, belts in pulleys or belts on a flat drum all make sense to me. A chain on a vee pulley just seems wrong. A couple of things concern me. First there's no tensioner and as the chain stretches the synchronization between the two variable diameter pulleys is going to have to recalibrate to avoid slipping. Side loading the chain (compression) makes it more difficult to go around a bend and follow the pulley. The whole idea seems opposite of what Subaru has been trying to do in reducing friction.

Thats what i have been wondering too. Granted the chain wont stretch much, but that may be why there is a low tow limit on the car. Yes it uses ATF fluid.


nipper

[dborla01]

I am not a mechanical/techno wizard, however, my emotional response to cvt, suby is that it is great on a higher powered vehicle, such as Murano, talked about by another guy on this site.
Wife and I like powerful, efficient vehicles, but Suby 2.5 sure let us down on test drive a couple of weeks ago. Those paddle shifters were pretty superfullous and silly. However, a lot of folks aren't interested in powerful cars, but like efficiency of this design. Guess that is why Suby went for high mpg, at detriment of power, on and off throttle over distances.