"bhtooefr" (bhtooefr)
12/20/2016 at 07:21 • Filed to: fake shifting, toyota, lexus, hybrid, e-cvt, cvt, transmissions, smug alert, bullshift
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"bhtooefr" (bhtooefr)
12/20/2016 at 07:21 • Filed to: fake shifting, toyota, lexus, hybrid, e-cvt, cvt, transmissions, smug alert, bullshift | 4
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So, last time I posted here, I said I’d think about doing a piece on the Toyota/Lexus Multi-Stage THS-II. This is that piece, but I thought I was basically going to do a technical overview, not a rant.
Instead, I’ll let the video above, !!!error: Indecipherable SUB-paragraph formatting!!! , and !!!error: Indecipherable SUB-paragraph formatting!!! handle the technical overview part. It’s an interesting transmission - essentially an ordinary Toyota hybrid system, with a 4-speed automatic on the end of it. This is really an extension of the concept used by the GS 450h and LS 600h’s L110 transmission, which is also an ordinary Toyota hybrid system, with a 2-speed automatic on the end between MG2 (the main electric motor) and the output shaft, to the entire transmission and to a larger range of gearing. Basically, it extends the operating range of the transmission, allowing higher engine RPMs at low speed, lower engine RPMs at high speed (it’s hypothetically able to shut off the engine all the way to maximum vehicle speed, although in practice, it seems to only do this at 140 km/h or slower), and better efficiency overall.
So, the belief is that this thing is going to be applied to many - maybe all? - RWD Lexus hybrids. I also believe that it’ll eventually appear in trucks, as Toyota has a !!!error: Indecipherable SUB-paragraph formatting!!! depicting a very similar configuration (not identical, but then, the patent’s priority date was in 2007) with a low-range gearbox on the end of it - the improved operating range given by the gearing could greatly improve towing capability and the like for vehicles equipped with this setup. Because this will be in many different applications, this rant is going to be purely about the LC 500h application - Toyota may well tune it differently in other applications.
I’m going to rant about this graph, right here, from Toyota’s technical overview:
A version of this is also in the video above (although it doesn’t show the CVT control area for “10th” gear), and you can see acceleration runs in action in that video.
Also, note that I’m OK with a fake manual mode on CVTs and CVT-like transmissions - I can safely ignore that. (Although, this is a car that I’ll never buy, so I can safely ignore it too... but I’m still going to rant about it.) This, however, is enabled in drive , so full rant mode engaged.
The entire freaking point of a CVT is that it pins the engine at the ideal RPM for the current power demand, and the Toyota e-CVTs are quick about it, too (quick enough that they’re faking freaking gearshifts with this), and can use electric torque filling to remove at least some of the feel of waiting for the engine to rev up before you get the power.
This is faking gearshifts all the time (unless you’re above about 70 km/h, then it’s possible that you get into “10th gear”, which basically means 4th on the reduction box, and behave like a CVT on the power split device), although with the ability to “curve” the gear ratios to improve low-speed power.
This is literally making the car slower (less engine power) and less efficient - and from what I’m reading, without the ability to disable this - purely to appease some people who prefer the feel of antiquated automatic gearboxes. It might add a bit of jerk, which would add to the feeling of acceleration, but at the expense of actual acceleration.
And, I should be clear, I like driving manuals, too, but I despise stepped automatics, and this is an e-CVT (with a stepped automatic on the end of it, true, but the e-CVT can mask the shifts if done right, as in the old Toyota L110), a transmission type I actually like.
Manufacturers, don’t do stupid fake gearshifts on your CVTs, really. Or, if you do, make it so the end user can disable that shit.
jimz
> bhtooefr
12/20/2016 at 07:38 |
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How different is this from the two-mode transmission developed by GM, BMW, and DCX?
pip bip - choose Corrour
> bhtooefr
12/20/2016 at 07:53 |
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eight “gears” more than necessary.
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bhtooefr
> jimz
12/20/2016 at 07:54 |
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It’s fundamentally a different strategy - that particular 2-mode transmission had four real fixed gears, and two e-CVT modes (IIRC derived from 1st and 2nd fixed gears - shifting to the second e-CVT mode required shifting through 2nd). In addition, the two e-CVT modes worked differently - the first was an input split, the second was a compound split. So, there were six configurations that that gearbox could be in, all with different power flow characteristics, and only two of them had CVT behavior.
This gearbox is merely an input split e-CVT, no multi-mode weirdness, but with a 4-speed reduction box on the end. All four speeds have CVT behavior naturally, the “fixed” gears here are purely simulated in software.
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bhtooefr
> pip bip - choose Corrour
12/20/2016 at 08:09 |
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I’d say at least three of the reduction gears make sense - the fourth is probably helping low-load freeway efficiency, though. But, they can mask those shifts...
BvdV - The Dutch Engineer
> bhtooefr
12/20/2016 at 08:50 |
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I understand that they want to use some kind of gearbox for further reduction, to keep the e-CVT within a more efficient band, but making the shifting noticeable makes no sense at all outside of a sport mode.
Also, I don’t think much jerk is added by this transmission, seeing that it only uses planetary gears, whereas most of the jerk in a conventional automatic is caused by the torque converter, if I’m not mistaken.(slush boxes are not really common here in the Netherlands)
Can they also please stop calling the reduction gears a ‘multi stage shift device’.
EL_ULY
> bhtooefr
12/20/2016 at 09:07 |
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y so angry
Cé hé sin
> BvdV - The Dutch Engineer
12/20/2016 at 09:38 |
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Any jerks are caused by the clutches and brake bands that do the gear changing - the torque converter is used partially to damp any jerkiness.
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bhtooefr
> BvdV - The Dutch Engineer
12/20/2016 at 09:45 |
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And it’s not only making the shifting between reduction gears (the 3-4, 6-7, and 9-10 shifts being shifts between reduction gears) noticeable, it’s also making completely fake shifts (the 1-2, 2-3, 4-5, 5-6, 7-8, and 8-9 shifts). In a WOT acceleration run, it’ll “shift” seven times (ending up in virtual gear 8), when in reality it’s only shifting twice (ending up in third in the reduction box).
There will be some change in acceleration, though, with each shift - my understanding is that jerk is merely the rate of change of acceleration (which is itself the rate of change of velocity), and there will be that change if it’s changing “gear”. The torque converter in a conventional automatic actually smooths the shifts, reducing jerk (by unlocking during shifting, or just not being locked until you’re in top gear in really old ones).
Another thing I’ve noticed is that they appear to be switching which gearbox they refer to - sometimes it’s the L210, a single-speed e-CVT used in the IS/RC/GS 300h (the engine doesn’t go through the MG2 reduction gearing in that transmission), and sometimes it’s the L110, the 2-speed e-CVT used in the GS 450h and LS 600h (the engine DOES go through the 2-speed reduction box in that one).
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BvdV - The Dutch Engineer
> Cé hé sin
12/20/2016 at 09:45 |
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Ah I see, while I did have a course in university on gearboxes, I never really understood the details of automatic gearboxes to full extent.
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BvdV - The Dutch Engineer
> bhtooefr
12/20/2016 at 10:45 |
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The only reason I can think of for them implementing it like that is to make it seem ‘sporty’, but 7 shifts for a WOT run is just too much. Maybe my image of the LC500h is wrong, but I’m seeing it as a comfortable cruiser, so why not make the drive-train buttery smooth right?
My understanding of what you meant by jerk was wrong, leading to my misinterpretation, I get what you mean now.
It seems like the marketing department tried to understand stuff, and got confused between the two gearboxes (actually I think in this case a better term is power conversion unit) for some reason, since it is obviously an evolution of the L110, with regard to the usage of the reduction. Maybe it shares other parts with the L210?
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bhtooefr
> BvdV - The Dutch Engineer
12/20/2016 at 11:23 |
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Do note that that’s a WOT run from zero to the speed limiter that you’d get seven shifts, but still.
And, the LC is a bit of an oddball - it’s clearly a big comfortable grand tourer, but it’s apparently also trying to be really sporty for the class. It’s apparently positioned primarily against the BMW 6-series, the Mercedes S-class coupe, and the Jaguar F-Type, but benchmarked against the 911. (Some of that may be for the V8 model, which isn’t a hybrid, and has a conventional 10-speed automatic, though.)
I wouldn’t be surprised if, mechanically, this gearbox does share more with the L210 than the L110. The L110 is a really old design, having come out in 2005, whereas the L210 came out in 2013.
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bhtooefr
> bhtooefr
12/20/2016 at 12:46 |
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And, actually, I’m wrong here - they actually do just have a 2-speed MG2 reduction on the L110, whereas the L310 (I did find a document saying that the LC 500h’s gearbox gets that designation) has a 4-speed reduction on the entire thing.
On the L110, the power split device’s ring gear (output) goes directly to the transmission output shaft, and there’s a planetary gearset with 2 speeds gearing MG2 to the axle. So, the engine never actually sees a shift. (That also explains the weird behavior before MG2 shifts into 2nd when a L110-equipped car is doing a top speed run, where the engine never reaches redline until after the shift - because MG2 probably can’t handle the electrical path power.)
Here’s a diagram of the L110's layout:
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bhtooefr
> bhtooefr
12/20/2016 at 12:51 |
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Too late to edit this comment, annoyingly, but turns out, I’m wrong about the L110 - the engine doesn’t go through it, only MG2. Hopefully this, or my more detailed comment, shows up.
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Cé hé sin
> BvdV - The Dutch Engineer
12/20/2016 at 14:55 |
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They start off fairly simple. You have an epicyclic gear set. Lock any two elements together and you get direct drive. By locking one element you can easily obtain a forward reduction gear and a reverse one so you have a two speed (plus reverse) box and that’s how they started off. Add a second epicyclic and use that to provide a direct gear (which doesn’t have any effect) and a reduction gear which is used to speed up the output of the first gear set when it’s in first gear, thus making it second. Now you’ve got a three speed and they were made like this for decades. Then add a third gearset, after which it becomes witchcraft. It’s the same idea though, you mix and match the gearsets so you speed up and slow down their outputs. The nine and ten speeds being made now use four gearsets.
LongbowMkII
> bhtooefr
12/20/2016 at 17:49 |
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bhtooefr
> LongbowMkII
12/20/2016 at 17:50 |
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tl;dr: If you’re making a transmission that can behave as a CVT, don’t try to pretend it’s not a CVT and give it fake shift points instead.
Here’s an example of Subaru’s CVTs faking shift points at moderate throttle (light throttle gets rid of them because it’s not noticeable, heavy throttle gets rid of them to improve acceleration, as I understand):
Note that this Lexus “10"-speed is actually shifting even at wide open throttle.
Anima
> bhtooefr
12/20/2016 at 19:39 |
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My god. That video is marketing wank in it’s distilled form.
and 100 more
> bhtooefr
01/04/2017 at 10:32 |
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You are so right, sir.
Mid-90's Williams CVT-equipped F1 car...
... that was immediately and irrevocably banned. The CVT test car was several seconds quicker around the track than it’s conventional counterpart, and according to the driver, much smoother and easier to handle without all the gear changes.
http://www.f1fanatic.co.uk/2007/05/03/banned-continuously-variable-transmission-cvt/
A Tesla has a single speed reduction, and i don’t hear any complaints from their owners about the lack of simulated gear changes.