"LuczOr" (LuczOr)
05/21/2015 at 11:18 • Filed to: None
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"LuczOr" (LuczOr)
05/21/2015 at 11:18 • Filed to: None | 1
| 5 |
Let me start by stating that I am a die hard manual transmission guy. Nothing compares to rowing your own and I stand by my word via my refusal to own any car, regardless of how cool, if it doesn’t come with an H-pattern.
Due to the fact that I travel a lot for work, I get the unfortunate pleasure of driving a wide array of rental cars. Sure, you can flog them till the wheels fall off and then play dumb when you turn it in, but almost all of these cars come with an automatic transmission. In more recent years, the CVT has been more and more prolific in the rental community, and as such, I have had a sufficient amount of time to “test” a large sampling of the slippery-slidey, torque transfering offerings from many marques. Surprisingly, my mood is always better after driving a CVT rental than it is after I get out of one equipped with a conventional automatic.
At this time I would like to acknowledge that the greater automotive community, namely the enthusiast branch, is well known for the gnashing of teeth and clawing of eyeballs at the mere mention of a CVT, but I believe this is an unjustified response. I find both transmissions to be generally boring since in many ways they behave exactly the same. Both the CVT and auto come with a locking torque converter (although CVT occasionally come with a locking hydraulic clutch) so they exhibit the same slushy starting until they lock up. However, after this point the CVT beats the auto, in my book.
These transmissions exist to make things easier for drivers by removing the involvement of controlling the gears from the driver. Essentially turning a car into a machine where the driving style consists of “push this button to go.” When I get into a car with an auto or CVT, I pretty much relegate myself to this mentality. I don’t care what the transmission is doing, because I realize it’s going to do things wrong all the time. The difference is, the automatic reminds you that it’s doing things incorrectly every time it kicks you in the back when your not expecting it, while the CVT just gives you torque based on where you put the “go button.”
CVT is a much better system for the transportation appliances of today. The goal of the transmission is to be completely invisible to the driver while giving great fuel economy. Obviously the CVT beats the auto in the fuel economy battle since it has significantly lower rotating mass, a torque converter that can stay locked as soon as you have left a stop and a nearly unlimited ability to keep the engine in the most efficient operating zone for the current driving requirements. For a driving enthusiast like myself, making the automatic transmission invisible when I am forced to drive one is just fine.
But you should see how I drive the 540i when I get back home after a week of driving one of those terrible transmissions. Nothing beats slamming gears and chirping tires.
BoxerFanatic, troublesome iconoclast.
> LuczOr
05/21/2015 at 12:44 |
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The problems I see with CVTs, and I tend to agree with you about the appliance nature of the application...
... is that the CVT takes even more coddling and insulation from sharp torque changes than an automatic gearbox does. It still uses a torque converter, rather than a clutch, not even an automated clutch... and some CVTs might even use two torque-limiting devices to avoid shocks coming back from the down-stream driveline when coasting.
The belt/chains have torque and traction limitations, and the transfer pitch contact points are usually quite small on the outer edges, which doesn’t give much traction to avoid mechanism slippage, if I am understanding the operation correctly.
It may be simple for an push-button-and-go solution, but in an evasive maneuver, or in inclement conditions, especially with all four wheels engaged, such as a Subaru application, the CVT becomes the weak point in the drive line.
The sad part is, Subaru seems to be pushing CVTs into their entire lineup. I am not sure that there are any 5-speed automatic gearbox applications left anymore, with the demise of Tribeca, and the CVT application in the 3.6R Outback.
The 5EAT had Variable Torque Distribution 65% rear biased AWD, which IIRC, Lineartronic CVT has 90% front-biased variable-torque engagement AWD, more like other vehicles that have Haldex-style viscous coupling AWD. That used to be a Subaru advantage, now it is no big difference.
5 and 6-speed manual gearboxes are now only available on very BASIC packages of Impreza (not the “Sport” version, incidentally), XV Crosstrek, and Forester, and the few remaining options of performance-oriented Subarus, like WRX, STI, and RWD-only BRZ.
manual gearbox AWD cars are getting RARER... and the manuals are not being replaced by automated-clutch gearboxes... but by multi-ratio gearboxes, and CVTs that are less driver-’accountable’, shall we say.
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LuczOr
> BoxerFanatic, troublesome iconoclast.
05/21/2015 at 13:01 |
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I understand your concerns with the change of power distribution for AWD vehicles like the Subaru. I guess that matters if you’re driving in inclement weather. Addressing the chain slippage, this should never happen in normal driving conditions, even under full power. Once again, you’re right that it might slip in inclement weather when getting a serious jerk through the drivetrain, such as going from slipping on snow to gripping on bits of pavement. That being said, Nissan recently sent out a TSB to correct slipping CVT’s. In other words, if it’s slipping, it’s broken.
I also found it interesting that you mentioned Subaru’s CVT since I basically consider the Lineartronic CVT the best one I’ve driven and not because of it’s CVT behavior, but because of the faux “manual” mode. For some unknown reason (most likely because Subaru has some enthusiasts tuning these things) they tuned the faux gear changes very aggressively in Sport#. If I get lucky enough to score an Impreza rental, I always put it in manual mode and clicking through the “gears” can actually be described as fun.
Rock Bottom
> LuczOr
05/21/2015 at 13:03 |
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CVTs have higher parasitic losses than conventional automatics. That’s why not everyone has bought into them.
Peptide
> LuczOr
05/21/2015 at 13:05 |
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I don’t care about the philosophical issues surrounding CVTs, or any other transmission for that matter. But the torque-transfer methods used in today’s variable-geometry CVTs are among the worst engineering compromises in ground transportation. These are not robust and efficient devices, due to the pumping losses for the hydraulics (much higher than a planetary automatic) and...the ‘belt’.
These are one of the few technologies that I simply would have in one of my cars - period.
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LuczOr
> Peptide
05/21/2015 at 13:10 |
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I certainly wouldn’t have one in one of my vehicles either, but when required to drive one, I’m less upset than when required to drive an automatic.