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#3427143 - 07/17/14 05:21 AM Re: CVT with shift sensation [Re: wing0]
SteveSRT8 Offline


Registered: 10/10/08
Posts: 14777
Loc: Sunny Florida
Originally Posted By: wing0
I looked at some videos of cvt that goes through shifts. I noticed the rpm drops but not sure if it's a real or fake drop.

Does the transmission pause the movement of the belt for that split moment or it disconnect engine and transmission like a clutch?

Maybe these cvt 2.0 will require more frequent fluid changes?


The whole advantage of the CVT is continuously variable ratios. There is no interruption of power flow, only torque reduction in many applications to protect the unit itself...
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#3427147 - 07/17/14 05:34 AM Re: CVT with shift sensation [Re: Hokiefyd]
demarpaint Offline


Registered: 07/03/05
Posts: 21114
Loc: NY
Originally Posted By: Hokiefyd
Originally Posted By: gregoron
Either get an automatic or a stick if you want shift sensation.


The point is that CVTs are increasingly replacing automatics altogether, and the customer has no choice but the CVT. The nice part about it is if they want the smooth feel of the CVT, they can have it. If they want the feel of a stepped transmission, they can have it. Flexibility is great.


I hear ya, but what about durability and longevity? As long as there's a market for Pickups and larger SUV's for people who tow, I think the "traditional automatic" transmission will be around until they can beef up the CVT. hide Which is probably one reason ZF is making 8 and 9 speed units and pushing for more gears.
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#3427160 - 07/17/14 06:12 AM Re: CVT with shift sensation [Re: Hokiefyd]
d00df00d Offline


Registered: 10/20/05
Posts: 9156
Loc: PA
Originally Posted By: Hokiefyd
Variable ratios are boring to me. They further isolate the driver from the actions, from the feel, of the powertrain. I don't want that isolation. I want to feel it work. I want to hear it work. I actually LIKE that about stepped transmissions. I don't have manual transmissions in our vehicles for a few reasons, but it doesn't mean that I want to miss that feeling, that sensation, of a good engine/transmission combo going about its business.

The stepless feeling with a CVT IS the sensation of an engine/transmission combo going about its business. You're no more isolated from that than you are from the workings of a normal automatic.


Originally Posted By: Hokiefyd
I don't have a problem with the mechanicals of a CVT. I like simple. I like easy. As a CVT owner, I would want to have a "D" mode where it would do its thing just like any other CVT. If I'm shuttling co-workers to lunch, or if my wife is driving the car, or if I'm just in the mood for quiet and smooth, "D" works. But I also want an "M" mode with paddle shifters so that I can work it up and down "through the gears" if I want to hear and feel the powertrain work.

Again, the steplessness IS the sound and feeling of the powertrain working. I'm still not sure what you're talking about here.

I dislike the feeling and sound of a CVT, too. But I dislike the feeling of automatics by definition, so...
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#3427189 - 07/17/14 07:20 AM Re: CVT with shift sensation [Re: d00df00d]
Hokiefyd Online   content


Registered: 06/24/04
Posts: 11198
Loc: North Carolina
Originally Posted By: d00df00d
Again, the steplessness IS the sound and feeling of the powertrain working.


It's really not. With a stepless transmission, you push the accelerator and the engine revs up to a point where the software believes the engine provides the best combination of power and efficiency, and it continually varies the ratios to keep the engine there. It drones. It's a constant HUMMMMMMMM as the car accelerates forward. Smooth for sure. But it sounds like a constant speed vacuum cleaner. Or a boat. Or a go kart with a centrifugal clutch. There's very little change in the way the powertrain sounds. I don't like that. It's boring; it's monotonous. It's drab. Stepped ratios provide different sounds and feels from the powertrain.

And then on the other hand, where you might WANT a constant engine speed (like to hold a gear through twisty corners), a conventional CVT without step control can't offer that. If you're on and off the throttle, that CVT is going to cycle the engine up and down and not keep the engine cooking where you want it to. CVTs offer no control; with a stepped transmission, automatic or otherwise, the driver has full control over the engine.

I like control over the engine, as apparently you do. Because of a foot injury my wife sustained years ago, a clutch pedal in our cars is out. What's the next best thing? The ability for me to control engine speed through ratio selection. Stepless CVTs don't offer that, and I'm not interested in them for that reason. Give me ratio control with a CVT, even if it's a separate "M" mode or something, and I'd be happy with it.
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#3427194 - 07/17/14 07:23 AM Re: CVT with shift sensation [Re: demarpaint]
Hokiefyd Online   content


Registered: 06/24/04
Posts: 11198
Loc: North Carolina
Originally Posted By: demarpaint
I hear ya, but what about durability and longevity?


Don't get me wrong; I'm not promoting CVTs. I'm saying that if my only choice in "automatic" transmission in a vehicle is a CVT, then I would like the ability to control it to some degree. Paddle shifters would be fine.

In the CVTs I've driven to date, the driver has ZERO control over what's going on. At least with a stepped automatic, you can dictate engine speed through gear selection.
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#3427210 - 07/17/14 07:43 AM Re: CVT with shift sensation [Re: SteveSRT8]
supton Online   content


Registered: 11/09/08
Posts: 4666
Loc: NH
Originally Posted By: SteveSRT8
C'mon guys. Shift shock? Whazzat? No modern automatic trans has any. Retarded timing and throttle reduction are precisely timed in many cars so you don't feel nuttin' unless you got your foot in it.


My 4 year old truck definately has shifts that can be felt. I won't say neck snapping but you know they occur.

*

I still haven't heard of a good answer to my question: how would you have manual control over a CVT otherwise?
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#3427371 - 07/17/14 10:31 AM Re: CVT with shift sensation [Re: supton]
KrisZ Offline


Registered: 12/23/06
Posts: 4262
Loc: Toronto, Canada
Originally Posted By: supton

I still haven't heard of a good answer to my question: how would you have manual control over a CVT otherwise?


I'll take a stab at that one.

Essentially, in order to have a full control over a CVT transmission, you would need a sliding lever, sort of like a dimmer. The ends of the lever's movements would represent the highest and lowest gear ratios and everything in between would be dictated by lever position.
The problem with this approach would be the need to constantly adjust the lever and the gas pedal position. Since there would be no gates, one would have to smoothly slide the lever back and forth to adjust the speed. That would be a major headache even for enthusiasts.
This is why the stepped CVTs are being implemented for those wanting to have some sort of manual control.
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#3427436 - 07/17/14 11:26 AM Re: CVT with shift sensation [Re: wing0]
supton Online   content


Registered: 11/09/08
Posts: 4666
Loc: NH
Personally I think it's a great idea. Think about this: you could program it to have say 5% steps in "race" mode. In "fun" mode you could have say 10% steps while accelerating, and say 20% downshifts--that way, it accelerates reasonably well, loaf along in a high gear--then with a click or two be deeply geared for passing. Without having to hit down ten times.

Imagine that: with a bit of software work, you could have as many (or few) gears as you wanted. And then when you aren't in the mode, set it to CVT mode. And then change your mind next week and redo it.
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#3427633 - 07/17/14 02:39 PM Re: CVT with shift sensation [Re: wing0]
Miller88 Offline


Registered: 04/09/08
Posts: 6519
Loc: Onondaga County
Having driven a few of them, I am doubtful that anyone consulted a BSFC chart for the engines.

The Nissans either lug the engine too much or have it running at redline all the time.

Seems like it would be possible to program in the BSFC chart and have it set the RPM according to throttle input (ie - low throttle, I don't want to accelerate fast, medium throttle - put it where it has the most volumetric efficiency , full throttle - best torque ,horsepower).
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#3427966 - 07/17/14 09:29 PM Re: CVT with shift sensation [Re: wing0]
buster Offline


Registered: 11/16/02
Posts: 29148
Loc: NJ
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#3428055 - 07/17/14 11:48 PM Re: CVT with shift sensation [Re: Hokiefyd]
d00df00d Offline


Registered: 10/20/05
Posts: 9156
Loc: PA
Originally Posted By: Hokiefyd
Originally Posted By: d00df00d
Again, the steplessness IS the sound and feeling of the powertrain working.


It's really not. With a stepless transmission, you push the accelerator and the engine revs up to a point where the software believes the engine provides the best combination of power and efficiency, and it continually varies the ratios to keep the engine there. It drones. It's a constant HUMMMMMMMM as the car accelerates forward. Smooth for sure. But it sounds like a constant speed vacuum cleaner. Or a boat. Or a go kart with a centrifugal clutch. There's very little change in the way the powertrain sounds. I don't like that. It's boring; it's monotonous. It's drab. Stepped ratios provide different sounds and feels from the powertrain.

Do you just not like it, or do you really think it represents greater isolation? Those are two different ideas.


Originally Posted By: Hokiefyd
And then on the other hand, where you might WANT a constant engine speed (like to hold a gear through twisty corners), a conventional CVT without step control can't offer that. If you're on and off the throttle, that CVT is going to cycle the engine up and down and not keep the engine cooking where you want it to. CVTs offer no control; with a stepped transmission, automatic or otherwise, the driver has full control over the engine.

Assuming the stepped transmission in question allows manual gear selection, this part makes sense.

If we're comparing a CVT to an automatic WITHOUT manual gear selection, I don't see how a stepped transmission offers any non-trivial kind of additional control. With a CVT, you mash the gas and then wait for the revs to climb; with a stepped automatic, you mash the gas and then wait for a downshift. Either way, there are annoying delays and the possibility of hunting for the right ratio.


Originally Posted By: Hokiefyd
I like control over the engine, as apparently you do. Because of a foot injury my wife sustained years ago, a clutch pedal in our cars is out. What's the next best thing? The ability for me to control engine speed through ratio selection. Stepless CVTs don't offer that, and I'm not interested in them for that reason. Give me ratio control with a CVT, even if it's a separate "M" mode or something, and I'd be happy with it.

Why have a CVT at all, then? A decently programmed 8-speed automatic, let alone a DCT, would blow it away in the manual mode without giving up much efficiency.
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#3428132 - 07/18/14 04:45 AM Re: CVT with shift sensation [Re: d00df00d]
SteveSRT8 Offline


Registered: 10/10/08
Posts: 14777
Loc: Sunny Florida
Originally Posted By: d00df00d
Why have a CVT at all, then? A decently programmed 8-speed automatic, let alone a DCT, would blow it away in the manual mode without giving up much efficiency.


An EXCELLENT question!
_________________________
"In a democracy, dissent is an act of faith."
J. William Fulbright
Best ET-12.79 @ 111 mph
4340 pounds, Street tires
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#3428184 - 07/18/14 06:50 AM Re: CVT with shift sensation [Re: wing0]
supton Online   content


Registered: 11/09/08
Posts: 4666
Loc: NH
How many cars offer a choice between an 8-ish speed conventional auto and a CVT?
_________________________
2004 VW Jetta Wagon, TDI, 5spd manual, 299kmile, his
2011 Toyota Camry, base, 6spd manual, 78k, hers
2010 Toyota Tundra double cab, 4.6L, auto, 88k

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#3428191 - 07/18/14 07:10 AM Re: CVT with shift sensation [Re: d00df00d]
demarpaint Offline


Registered: 07/03/05
Posts: 21114
Loc: NY
Originally Posted By: d00df00d

Why have a CVT at all, then? A decently programmed 8-speed automatic, let alone a DCT, would blow it away in the manual mode without giving up much efficiency.


Good question. I'd also be willing to bet the 8 speed would be stronger, last longer, and have a higher tow rating than a CVT. That's what I'd be looking for.
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#3428193 - 07/18/14 07:10 AM Re: CVT with shift sensation [Re: SteveSRT8]
Shannow Offline


Registered: 12/12/02
Posts: 26513
Loc: a prison island
Originally Posted By: SteveSRT8
Originally Posted By: d00df00d
Why have a CVT at all, then? A decently programmed 8-speed automatic, let alone a DCT, would blow it away in the manual mode without giving up much efficiency.


An EXCELLENT question!


From a systems reliability perspective, the more things that you put in series, versus parallel reduce reliability. e.g. if you are designing a pump train and need multiple pumps in series, and they are (say) 90% reliable (each), two pumps in series will be 81% reliable, three pumps 72 and on.

In the case of extra speeds in a tranny, if each has a similar failure rate, an 8 speed will be far less reliable than a 4 with the same components....from a packaging perspective, 8 has to have smaller componentry for carrying the torque loadings, clutches etc.

As evidenced, they can make multi speed autos as reliable as they need to be...but complexity has its own issues.

Don't get me wrong, I'm not a CVT die hard. Until a few weeks ago, I disliked the driving experience (Maxima had "stepped" programmed into sport, and a "manual"hold mode which I liked)...Industrially, I've had to babysit them over the decades, and would prefer not to use them.

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