The CVT: Learn it and Love it - Subaru Forester Owners Forum
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post #1 of 319 (permalink) Old 10-31-2013, 01:05 PM Thread Starter
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The CVT: Learn it and Love it

The CVT and acceleration expectations.

Before the CVT there was the manual transmission and the automatic transmission. While the automatic transmission masked a lot of driver inexperience through their electronic/hydraulic controls, the manuals required the driver to provide the control between the engine and the wheels.

Anyone with experience knows when a MT is driven poorly... stalling, jerking, and the rest. But there are more serious consequences for driving a MT incorrectly, and some require engine rebuilds. Some are for spun bearings, some are for pistons with broken ringlands, and some are both. All because the driver didn't know how to manage the vehicle's torque with gearing vs RPM. But regardless of whether these mechanical failures occur, there is a certainty that at the least poor gas mileage occurres. Add in clutches, gears, and synchronizers to the mix and it's clear the Manual Transmission requires an intelligent and skilled operator... or else.

Automatic transmissions, on the other hand, are easy. Modern automatics "think" for us. They have a Transmission Control Unit, or TCU, similar to the ECU, that does the thinking for the driver... even if they are inexperienced. Once CAN Bus OBDII became standard (CAN bus - Wikipedia, the free encyclopedia) vechicles became even smarter, and the engine and transmissions along with other systems, all cooperate behind the scenes. Paddle shifters, rev-matching downshifts and upshifts, and simply smashing the go pedal all get interpreted by the control systems that then provide what the driver wants without fanfare. Pretty nice.

How does a driver of a manual transmission break a ringland or spin a bearing... and that those events are less likely in an automatic-equipped car? One scenario is when the MT driver is driving along in high gear and decides to go WOT, for whatever reason. Another is going at a slower speed in third or fourth gear at lower RPMs... and puts the pedal to the metal. In both cases the gearing is too high to permit the engine to move the vehicle very fast. This is where the trouble begins... going WOT tells the ECU to go to a set of circumstances governed by tables, called Open Loop. In OL there is a fixed value per RPM and Requested Torque for fuel, timing, AVCS, Boost etc. If the car cannot accelerate fast enough due to too high a gear, the airflow cannot sustain those requests and the engine works poorly at best. At worst it causes huge loads on the bearings and operating conditions that cause detonation. Not good. Where the AT would downshift or decouple the TC, the MT in the wrong gear labors.

There is simply not enough room in a single post to present the total picture that supports these facts. Reader research, however, will provide corellation. Simply put, the issue is Ramp Rate. Require a vehicle to accelerate faster than it can physically respond to... and it will work poorly, mostly because of tuning parameters and airflow. Open the throttle to maximum without the gearing that allows the vehicle to fulfill that torque request (move forward) and it balks... pounding the bearings and pistons, falling on its face, and wasting gasoline.

The new CVT is a next-generation transmission, controled by the synergy of a combined ECU/TCU/BCU CANBUS "mind" that prevents the unitiated from ruining Subaru's intentions. Subaru wants their vehicles to be pleasant and easy to drive, to get good gas mileage, and be reliable... despite drivers who don't care about such things.

Therefore, vehicles equipped with Subaru's latest CVTs accelerate fastest at "partial throttle" as so many have discovered, because, to Subaru, the reliability of the machinery is more important than 0-60. To Subaru, the prevention of destructive ramp rates' effects on the transmission and driveline, and the maximizing of gas mileage are priorities. You can work with it, but you are prevented from damaging it with injudicious use of controls. Find the throttle angle that matches the optimum Ramp Rate and you'll find extraordinary response. Smash the pedal to the metal and you will get the "safe" version to your request.

Skilled MT drivers, whether of automobiles or motorcyles, already know these things. Their numbers grow smaller and the people who treat automobiles as appliances grow greater. Technology is simply responding.

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post #2 of 319 (permalink) Old 10-31-2013, 01:30 PM
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Nice write up. Definitely things I hadn't considered. Thanks.


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post #3 of 319 (permalink) Old 10-31-2013, 02:36 PM
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My 2014 Forester is the first CVT I have owned, after many vehicles with manuals and regular autos. I do like it, but I would like it more if the darn thing didn't buck and jive for the first 10 minutes of operation, and light pedal. It's better now at 6000 miles than it was with less miles, but still needs some fix to make that go away completely. When I get the first oil change I will be telling them about the CVT buck, and hope it gets better with whatever update is needed.

I like new technology, but still appreciate running the Miata's slick 6 speed through the gears to seven grand using personal skill and my own decisions about when to shift, how to shift, and not always be governed by the machine.

As an old guy, I learned on a "three on the tree" ancient manual Chevy so I actually know how to shift gears and use a clutch. The new stuff is also neat to use, and overall the CVT will be evaluated when it is fully "off probation", which it is not, yet.

So far I would give it 3/5.

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post #4 of 319 (permalink) Old 10-31-2013, 02:47 PM
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The CVT on my '14 is my second, the first being on my 500cc Touring Scooter, and I've had zero complaints about either. In fact, so far I've been quite impressed with the smoothness and responsiveness. I've never experienced the bucking and jiving that others have so I feel that if you have it, something is wrong, whether mechanical or logical. It can't be normal because otherwise my CVT would be abnormal because I don't have these issues. Given the ancient maps and outdated software in the Head Unit, I suspect that Subaru hasn't been keeping on top of their code versions and there's a software glitch affecting some CVT's. Too bad we can't compare software versions.
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post #5 of 319 (permalink) Old 10-31-2013, 07:43 PM
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Nice write up. I had noticed this in our Legacy and tried to explain it to my wife. Blank looks all around.

I know nothing.
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post #6 of 319 (permalink) Old 10-31-2013, 09:05 PM
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Quote:
Originally Posted by lwerring View Post
I've never experienced the bucking and jiving that others have so I feel that if you have it, something is wrong, whether mechanical or logical. It can't be normal because otherwise my CVT would be abnormal because I don't have these issues.
Most people that mention low speed issues don't have an XT, which has a different (older) generation, and spec (HT) of CVT compared to the one in the 2.5L models. Throttle tip-in of the 2.5 is tuned differently from the XT. The torque converters differ as well.

Mine is smooth, and easy to drive at all speeds, whether cold or warmed up.

For something supposedly so numb and unengaging, there's a surprising amount of technique required to get the most out of the CVT. When just driving around though, it's pretty invisible.

Last edited by neall_v; 10-31-2013 at 09:13 PM.
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post #7 of 319 (permalink) Old 10-31-2013, 09:17 PM
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Fantastic. Should be elaborated and stickied for the next gen of MT drivers so they at least understand the "you are the torque converter" concept

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post #8 of 319 (permalink) Old 10-31-2013, 10:32 PM
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I love. My CVT in my XV
Best gearbox Subaru has made


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post #9 of 319 (permalink) Old 10-31-2013, 11:39 PM
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Thanks for your write up. I believe that using cruise control in hilly country can also cause the issues you are referring to. I know the Honda Civic manual shift I used to own ran at significantly higher revs in 5th gear than the auto transmission presumably to help compensate for this very issue.
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post #10 of 319 (permalink) Old 11-01-2013, 03:45 AM Thread Starter
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The transition to CVTs from previous generation transmissions, both MT and AT, came well after another transition that occurred long enough ago that many won't remember it... when fuel injection replaced carburetors. While that transition seems an unrelated event, it was also made in the interests of fuel economy and emissions, just like the CVT. But that long-departed change, while bringing far better driveability, fuel economy, and lower emissions, also created a driveability problem. This problem came not as a result of what fuel injection brought, but what was eliminated... that carburetor itself.

The carburetor of old had also transitioned during its use... mainly to accommodate the same issue at work here. With the carburetor gone it seemed that automotive engineers forgot that, or thought that fuel injection was a panacea that cured all. It didn't, it doesn't today, and that missing element the hidden little carburetor embodied was never incorporated into fuel injection systems. That missing element is the separate primary and secondary throttle bores that the engine breathed through... a design augmented by a progressive opening of the far larger secondary bores, compared to the small primaries.

The reason carburetors, on small and large displacement engines, were designed this way was to manage airflow during the transition from idle to maximum engine output. No airflow, no power. Wrong airflow, poor power. Et cetera. Again, Ramp Rates due to a varying RPM band managed by transmission capabilities, and driver abilities. This is not too different from what the CVT does today. But instead of bogging down if the throttle was opened too far in the wrong gear on a carbureted engine, the CVT-equipped vehicle's electronics deliver a seamless product that is the best, albeit interpreted, answer.

Cars without CVTs, including present generation WRX and STi, for example, still suffer the driver to provide the torque management function despite their state-of-the-art fuel injection systems. There is only one throttle body bore and it's rather huge. Going WOT opens that TB butterfly fully... without the aid of a little primary and progressive secondary like the carburetor has, nor a quick drop in gearing and loosening the engine-transmission coupling that the AT does. Big hole in the intake, wrong rev range selected by the gearbox, heavy vehicle, and the WRX or STi or whatever struggles. During that struggle, incorrect fueling and timing are delivered at crankshaft angles where mechanical leverage fights the oil barrier interface. In worst-case scenarios metal on metal contact will occur, and the driver will have no indication or feedback that their choices were wrong... until they hear that dreaded sound from inside the engine, rod knock. Damage to pistons' ringlands has more subtle telltales, but it is just as expensive a lesson.

The CVT and its electronic controls, along with a far better handshaking relationship with the engine's controls, prevents such destructive events. That is a very good thing, and more than a fair tradeoff for the consequential aberrances some experience as undesirable in its actions that do not fulfill their unrealistic expectations, in my opinion as well as, apparently, in Subaru's opinion. Some propose to change the equation with "tuning." They want to bypass the nannying and get their 0-60 fix. It may even happen... but it is guaranteed that such change will show the "why" of the way it is now, with broken drivelines.

That is why I'm learning how to get the most from this great transmission, not fault or fight it. Like a growing realization of many, I feel this is the very best transmission not only Subaru has ever made, but a game changer for the future. The CVT will undergo evolutionary changes that will refine it and make it even better, but the revolutionary event itself has already happened.

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post #11 of 319 (permalink) Old 11-01-2013, 05:27 AM
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Extremely informative write-ups. Thank you Fate.

This is my first Subaru and first CVT. I'm loving both.
I've owned both MTs and ATs, but have a soft spot for manual trannys. There's something about getting that perfect downshift. Be that as it may, I am learning how to better utilize the CVT in my FXT. Thru trial and error, mostly thru error in the beginning, I've experienced that phenomenal acceleration that you get when you do find that sweet spot between throttle position and ramp rate. It never fails to leave a smile on my face.

Despite several naysayers, "don't get a Subaru", don't get A CVT", I did, and I haven't looked back. Those, like my brother in law, that finally got to drive my ride said "wow, this drives and handles great!...wait, this is a CVT?!" Haha, Yes, this is a CVT. I also can't help loving the fact that the 2014 Forester won MTs SUV of the year. I'm not letting the naysayers forget that fact either.

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post #12 of 319 (permalink) Old 11-01-2013, 07:30 AM
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I drove a 2014 with the CVT for 2 months and was impressed with it. I like it quite a bit. I perfer MTs.

I still prefer having control over the shifting and would probably still go with a MT in the Forester, however, the CVT is not a bad alternative. Reality is though, MTs are fading fast.
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post #13 of 319 (permalink) Old 11-01-2013, 08:13 AM
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Quote:
Originally Posted by Fate View Post

The CVT and its electronic controls, along with a far better handshaking relationship with the engine's controls, prevents such destructive events. That is a very good thing, and more than a fair tradeoff for the consequential aberrances some experience as undesirable in its actions that do not fulfill their unrealistic expectations, in my opinion as well as, apparently, in Subaru's opinion. Some propose to change the equation with "tuning." They want to bypass the nannying and get their 0-60 fix. It may even happen... but it is guaranteed that such change will show the "why" of the way it is now, with broken drivelines.

That is why I'm learning how to get the most from this great transmission, not fault or fight it. Like a growing realization of many, I feel this is the very best transmission not only Subaru has ever made, but a game changer for the future. The CVT will undergo evolutionary changes that will refine it and make it even better, but the revolutionary event itself has already happened.
You are missing the point altogether, and your post, while perhaps not intentionally, has a condescending air. The CVT in my NA Premium should perform the desired function without the need to find fault or fight the transmission. It should simply perform as intended. A widely occurring tendency within the 2014 Forester CVT equipped models to surge and buck under light pedal until fully warmed (and not just to engine operating temperature, but more) is a defect in the vehicle, not in the driver. We don't need to somehow adapt or learn a new product, the product needs to perform as designed. Things happen and they need to be fixed sometimes, so be it. It shouldn't necessitate a long winded lecture about what we should get used to doing or that such problems are because we don't know how to drive such advanced systems. Probably a majority of Americans now driving cannot drive a stick shift clutch car, but a CVT? It's not made to be hard to drive, just the opposite.
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post #14 of 319 (permalink) Old 11-01-2013, 08:32 AM
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Well first off, not all users report this issue - just some do.
I bring this up because of those few, many have reported the problem disappearing or getting a whole lot better after 1k miles or so.
I think proper weightage should be given to the possibility of users being more consistent with their foot and learning to do that over time. It's hard for me to say this isn't a Subaru 'bug' but I would imagine user behavior is a significant factor.

Quote:
Originally Posted by EddieJoe View Post
You are missing the point altogether, and your post, while perhaps not intentionally, has a condescending air. The CVT in my NA Premium should perform the desired function without the need to find fault or fight the transmission. It should simply perform as intended. A widely occurring tendency within the 2014 Forester CVT equipped models to surge and buck under light pedal until fully warmed (and not just to engine operating temperature, but more) is a defect in the vehicle, not in the driver. We don't need to somehow adapt or learn a new product, the product needs to perform as designed. Things happen and they need to be fixed sometimes, so be it. It shouldn't necessitate a long winded lecture about what we should get used to doing or that such problems are because we don't know how to drive such advanced systems. Probably a majority of Americans now driving cannot drive a stick shift clutch car, but a CVT? It's not made to be hard to drive, just the opposite.
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post #15 of 319 (permalink) Old 11-01-2013, 09:34 AM
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My friend and I were discussing this topic. I told him about the CVT and how I thought it was good in the new Forester. We both prefer MT's. He doesn't like CVT's all that much.

Quote:
There's no can bus obd2 protocol. There are can bus connections you can use via the diagnostic port, but it's not an obd2 can bus. It uses a serial bus signal. That's why any elm323 processor based OBD2 scanner using a T2t connect to any OBD2 port. The same reason why you can't plug an obd2 port to an obd1 port. Or even obd 0.

- A lot of cars don't have rev matching on down shifts (most high end cars do)

- Busted ring lands and spun bearings? If you over rev, your valves float. You break pistons, sometimes rods. You don't bust ring lands from spinning a motor too fast, you bust them from detonation or no oil and a piston ring catches. Thrust bearings will wear from poor downshifts if you let the clutch out fully and quickly in a low gear and the engine is at idle. And they'll WEAR, not spin. Unless you have a poorly built motor or you run out of oil/beat on your car when the oil is cold, you're not spinning bearings. Regardless, I have yet to see either. I love how he explains about the bearings, but not the ring lands blowing off.

- Requested torque is mainly used in bosch and delphi ecu feature. A lot of ecu's don't do this. They use different algorithms to adjust the throttle. Some cars don't even have throttles (I believe s54 motors)


bouncing off the rev limiter??? Downshifting over the redline? Bogging the motor? I don't know. Simple solution, know when to downshift, or don't do it, and don't bog the motor or leave it in a low gear.

- Ramp rate? Electronic throttles (drive by wire) smooth things out to make everything nice for the driver. Manual or automatic. Cable throttles are obviously a different animal. Once again, I have yet to see someone spin a bearing because they shift retardedly.

-"pounding the pistons" ??? Every piston gets pounded. That's why they call them 4-bangers. An explosion is pushing the piston down. The only part of the piston that's contacting anything are the wrist pins and where the piston rings contact the piston in the ring lands.

-partial throttle? Data log, the actual throttle position and throttle position requested. I'd love to see the results.

-I don't know what this has to do with anything, transmissions and throttles are two different things. The MS3 has a safety where it'll cut the throttle if it thinks the motor is going to blow. My R does the same.

-Automatics do the same thing, but they don't have wearable bands like the CVT's. Also most cvt's are still slower 1/4 and 0-60. I remember when nissan switched to one in the altima, the cvt was much slower.

Does it work, yep? Will people buy it, yep? But it's not to save the world from manuals and people blowing up their motors.

Last edited by MvNJ; 11-01-2013 at 09:53 AM.
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