Proof CVT not worth the hassel 3

[dicer]

http://content.usatoday.com/communi...e-8-speed-transmission-on-mainstream-models/1

I think most manufactures learned the cvt lesson. And have decided with 8 and higher speed automatic transmissions, with I suppose very close ratio. Makes alot more sense to me and likely them too.

 

[dicer]

http://www.motorward.com/2011/06/zf-9-speed-automatic-transmission-details/

More good stuff. Now why go through all this when you can have a cvt?
CVT's are like 8 track tapes.

 

[patprimmer]

And just two adds by two manufacturers each pumping their own product with all the marketing spin they can muster is all it takes to convince you? I have a very nice bridge for sale and can I do a deal for you.

Regards
Pat
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[JayMaechtlen]

Aside from sales/marketing, there's that great term "engineering tradeoff".


Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[NormPeterson]

dicer, I can sympathize with your dislike for engine rpm and road speed not remaining in lock-step with each other.

Conventional "shifting" automatic transmissions do the same thing, albeit only below either hydraulic or mechanical torque converter lockup. If the exhaust system is loud enough, this is clearly noticeable even when the vehicle is never seen.

What I don't understand is such a strong conviction that there must be something actually wrong with it. Yes, you might have to shop elsewhere, as I already have for that and similar reasons.


Norm

 

[dicer]

It has its place, and in an automotive transmission is not the place. Yes all will read the marketing into it. But there is a reason for not going with the CVT design. And if it was for nothing, for them to use conventional means in these 8 and 9 speed transmissons, it then makes no sense to use them. Why? Because CVT is the cheap way to go for manufacturing, way less parts involved. And as we all know any manufacture wants to go the path of least resistance when it comes to costs. I didn't think I would have to spell this out for all here. If you take the time to read info on the net by the previous owners of CVT vehicles you will see that many are very dissatisfied and will avoid those transmissions at all costs. A car company wants customers, more so than they want to build a cheap transmission that has a low life. Yes if you live in flat lands with no hills you may get big miles on them, but if you pull a trailer of some sort or live in areas with steep hills you may not.

 

[JayMaechtlen]

hmmm- As engineers we should automatically (sorry) avoid the lower cost route?
In many respects, a CVT seems pretty attractive. An 8-speed or 9-speed automatic has lots more 'stuff' to go wrong,
For performance, if the spread is good enough, you should be able to hold the engine at peak HP through the full acceleration run. If the efficiency is reasonable, you should match or beat even a 9-speed.
Do you have numbers for relative cost and efficiency for CVT vs. 8-speed or 9-speed?


Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[patprimmer]

Ihave seen some model epicyclic gear based automatics give warranty issues.

I have seen manual transmissions give warranty issues.

That does not mean the design principle is flawed.

I have seen people who will never ever buy a Ford again, Same for GM, Chrysler, VW, BMW, Honda, Nissan etc etc etc. Does that mean that all these and every other make is below market acceptable durability.

I will say it again. My brother has a Nissan CVT. He has had it for over 3 years. He does a lot of miles. He tows. He goes off road. We have hills and yes I know Aus is a flat continent, but Sydney is a hilly city and the eastern seaboard is a mountainous region. We as a family use our cars hard. We go places in family sedans that some won't go in a Land Cruiser. I found one car I had was equipped with a speed limiter as I was driving on a dirt outback road (police don't set radar traps on dirt roads).

So if the fact that I won't form a prejudice against CVTs on the spin in a competitors advertising or the anecdotal third hand evidence of an unreliable source surprises you, well I guess your in for a surprise.

If I see data from credible sources I will certainly review my opinion and consider maybe my satisfactory first hand real life experience was merely luck. Hmmm if luck is all it takes for one example of a design to work, that kinda implies failures are quality rather than design problems.

Regards
Pat
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[NormPeterson]

If you take the time to read info on the net by the previous owners of CVT vehicles you will see that many are very dissatisfied and will avoid those transmissions at all costs

You will also find staunch advocates, which is notable because people tend to register complaints long before praise.

I know of one individual who is fully as enthusiastic about the CVT in his 7th generation Maxima as I am hardcore about sticking [sorry] to conventional manual transmissions in my cars. He didn't get to that point by simply "putting up with it", even though he entered ownership of that car with at least a little trepidation.


Norm

 

[Tmoose]

There have been a few SCCA Solo mod and hillclimb cars that have used CVTs to good effect over the years.

http://www.youtube.com/watch?v=VHrfrl6DqjM&feature=related

At 0:47 the announcer says.....
"by far the fastest time ever on this hill. Everywhere he goes he sets records with this car"

 

[LionelHutz]

Work has a Murano with 260,000km give or take. The CVT is still working. No-one really cares either way for it. The info on autos with more gears doesn't really prove anything.

 

[dicer]

Jay, I agree way more costs for the 8 and 9 speed. So why are they doing it rather than a nice cheap CVT? If CVT is so great, how come you don't see them in heavy haul trucks, fire trucks, garbage trucks etc?

 

[swall]

Isn't the flexible metal belt that makes the CVT possible kind of expensive when you get into the bigger sizes?

 

[NormPeterson]

If CVT is so great, how come you don't see them in heavy haul trucks, fire trucks, garbage trucks etc?

At least for the Class 8 trucks, you absolutely need to have plenty of engine compression braking available. I just asked my son-in-law, and he estimates he gets into the Jake brake at least a hundred times a day, more if there's a lot of downhill (this was after he stopped snickering).


Norm

 

[patprimmer]

Regards
Pat
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[EdStainless]

garbage truck are the harshest trans service there is. Just think, three hours of stop and go 100' at a time followed by one hour of 75mph fully loaded. Then repeat. Just ask Allison where they test new automatics.
A CVT in small and med sized passenger cars makes great sense. These are too small to make 8 or 9 spd autos practical and the loads are fairly small.
The key to either of these (cvt or 9spd) is the EMC. By controlling both shifting and throttle together you get smooth transitions, minimize stress, and optimize efficiency.

Yes, the steady rpm while the car is accelerating is a bit disconcerting at first. I am very satisfied with the CVT in my Subaru Outback. They have handled the "shifting" issues very well. It does not always change gradually but under some conditions makes what feels more like traditional shifts.


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Plymouth Tube

 

[moon161]

Have a CVT in my ford escape hybrid, new to me at 95000 miles. Seems to be controlled to 2000 engine RPM (almost all the time), 1000 rpm (idle, car stopped, charging) or higher RPM depending on throttle position when accelerating. If you watch the tach, it looks like a slipping clutch, but otherwise commands zero notice except some engine noise when you accelerate fast. Why not control an engine to an efficiency peak or a power peak depending?

In 10000 miles, replaced an ABS exciter ring, needs a new thermostat. Looks like the rear pumpkin has been resealed, maybe the rear CV's were replaced. In NYS, hybrids have an extended powertrain warranty, I think 150k miles.

Opposite of my benz 240D w/ a 4 spd manual and a noise pedal where the gas pedal should be.

 

[KiwiME]

But the "CVT" in the Escape Hybrid is a totally different animal to what is being loosely discussed here, a metal belt-type CVT.

I would expect the Escape "CVT" to last virtually forever, as that of the Prius and others of that ilk.

I too am somewhat skeptical of the belt technology but cannot deny it works. A lot of cars and SUVs have them in this market.

 

[MikeyP]

I had a belt CVT (Jatco I think) on a Dodge Caliber/re for 3 years. You very quickly get used to the "motorboat" effect of revs not being linearly related to road speed - less than 1 week of living with the thing. The super-relaxed revs at high speed cruising was lovely. I really don't have a problem with them - they have a large parasitic loss from the pump that controls the pullys but then again so does an epicyclic auto or a DCT. The dodge had a torque converter for launch, but there are other designs out there that have a wet clutch instead - presumably for efficiency.

--
Dr Michael F Platten