CVT - simulated shifts - what are your thoughts and opinions?

[DrD123]

LOL, maybe for you in your GT, but for us 2.5r's

After driving a 19 Legacy 2.5i Sport for a month as a loaner I am going to have to say it's worse for the 2.5i - acceleration is, well... very gradual at such low rpm!

[YeuEmMaiMai]

This is not how my '15 operates.

 

Pegging the throttle will max out RPM...and then "shift"...and then shift again and again.

 

It's stupid and inefficient!

 

 

that's odd as the 15 16 18 and 19 loaners i drove all bypassed the shifting when WOT. CVT accelerates faster when it does not have to go between predefined shift points...

[hkshooter]

that's odd as the 15 16 18 and 19 loaners i drove all bypassed the shifting when WOT. CVT accelerates faster when it does not have to go between predefined shift points...

My 2016 3.6 doesnt bypass shifting at WOT. My wife's 2019 2.5 doesnt either.

 

Sent from my SM-G950U using Tapatalk

[gathermewool]

that's odd as the 15 16 18 and 19 loaners i drove all bypassed the shifting when WOT. CVT accelerates faster when it does not have to go between predefined shift points...

 

I'll pay more attention next time. I literally (thought I) stomped the pedal to the floor on two different on-ramps the same day I posted. Maybe I was actually at 99% throttle?

[ripstik]

Also, I LOVE how the CVT in our '14 FXT operates, WITHOUT the simulate gear shifting. At 1/2 to 3/4 throttle, it sticks at 3-4k RPM and boosts to 15+ psig and just GOES....

 

this is why it was banned in f1, peak boost combined with the best possible drive ratio at all times.... that and cuz everyone hated the way they sound.

[Burzendowski]

Is there a way to reset the shift points? During the winter months I was pretty heavy in the accelerator. Now that I’m not longer playing in the snow the car seems to prefer aggressive driving. Under slow acceleration I feel the car is in a higher “gear” than it should be.

[ammcinnis]

Is there a way to reset the shift points?

No.

 

Under slow acceleration I feel the car is in a higher “gear” than it should be.

Under slow to moderate acceleration you don't need to be in a lower "gear." "Lower gear" = Lower fuel efficiency and slightly more engine wear.

[gathermewool]

No.

 

 

Under slow to moderate acceleration you don't need to be in a lower "gear." "Lower gear" = Lower fuel efficiency and slightly more engine wear.

 

If he was driving aggressively, then did he mean a lower ratio, ie., higher RPM for lower load?

 

Clarification: engine wear is infinitesimally higher at lower RPM vs a higher RPM.

HOWEVER, I hate when my engine chooses a too-low RPM and I feel that god-awful vibration. The effect may be minimal, but over hundreds of thousands of miles, it definitely has an impact on mounts.

[ammcinnis]

Clarification: engine wear is infinitesimally higher at lower RPM vs a higher RPM.

Explain. It is generally considered that long-term engine wear is directly correlated with total crankshaft revolutions. Higher RPM => More crankshaft revolutions per mile traveled.

[Burzendowski]

So does the CVT learn driving habits from the day you buy the car or are the shift points predetermined and they never change?

[ripstik]

So does the CVT learn driving habits from the day you buy the car or are the shift points predetermined and they never change?

 

I was wondering the same thing

[tumbleweed 49]

So does the CVT learn driving habits from the day you buy the car or are the shift points predetermined and they never change?

 

I have seen a lot of opinions that the CVT "learns" shift points but no evidence. I think it doesn't learn at all but the EMS probably does and people think the CVT is changing. But I have no evidence for that either.

 

I tried mine last week and if I put my foot to the floor from a dead stop (shifter in D) it will shift the first time at 60 MPH, then again at 70. I did not go any faster because I was in a 50 MPH zone. I think the RPM was around 5700 or 5800. If I move the shifter to the M position, but do not use the paddle shifter, the shift RPM will be about 6300.

 

EDIT: Tried it again this morning and I detected a shift at about 45 MPH which would have been 1st to 2nd. The two listed above would have been 2nd to 3rd and 3rd to 4th I think. These are at full throttle in D. Speeds might be a little off because I look at the tach to tell when it shifts and by the time my glance has shifted to the speedometer it has changed.

Edited April 24, 2019 by tumbleweed 49

[SubieN8]

I have seen a lot of opinions that the CVT "learns" shift points but no evidence. I think it doesn't learn at all but the EMS probably does and people think the CVT is changing. But I have no evidence for that either.

 

I tried mine last week and if I put my foot to the floor from a dead stop (shifter in D) it will shift the first time at 60 MPH, then again at 70. I did not go any faster because I was in a 50 MPH zone. I think the RPM was around 5700 or 5800. If I move the shifter to the M position, but do not use the paddle shifter, the shift RPM will be about 6300.

 

The "shifts" should start around the 2,500-3,000 mark on up.

[gathermewool]

Explain. It is generally considered that long-term engine wear is directly correlated with total crankshaft revolutions. Higher RPM => More crankshaft revolutions per mile traveled.

 

Sorry, I was speaking practically, not of percentage actual wear.

 

Higher crank RPM with equivalent load will result in a much strong hydro-dynamic wedge. At low loads, the effective pressures are also low, so the required film strength is likely N/A as the wedge likely isn't compromised.

[gathermewool]

The "shifts" should start around the 2,500-3,000 mark on up.

 

I think it has more to do with accelerator position or requested torque than RPM. I've backed off the throttle after the first simulated shift, however, and it continues to simulate shifts until I back off the accelerator significantly.

[3p141592654]

Explain. It is generally considered that long-term engine wear is directly correlated with total crankshaft revolutions. Higher RPM => More crankshaft revolutions per mile traveled.

 

Actually not true. Peak bearing pressure and thinnest oil film occurs during the peak cylinder pressure on the power stroke and is worse (thinner) at low rpms. So the highest and most damaging loads occur at high bearing pressure and slow rpm, which is why lugging was discouraged in older times. These days you can model the film thickness under various conditions and design the bearing to handle it, but it is categorically not true that bearing wear is just a function of crankshaft revolutions, it is not that simple. If you can ensure a minimum oil film thickness then operating wear is negligible. For ring wear, I would agree with your comment.

 

This plot may help with understanding.

[ammcinnis]

Actually not true. Peak bearing pressure and thinnest oil film occurs during the peak cylinder pressure on the power stroke and is worse (thinner) at low rpms.So the highest and most damaging loads occur at high bearing pressure and slow rpm, which is why lugging was discouraged in older times.

First, I was talking about total engine wear, not just wear in the crankshaft journal bearings.

 

Second, when considering the crankshaft journal bearings you disregard reciprocating inertial loads (pistons, rods, etc), which are considerably higher than combustion loads throughout most of a modern engine's range of operating rpms.

 

If you can ensure a minimum oil film thickness then operating wear is negligible.

On that point we agree, at least for the hydrodynamic lubrication regime.

[3p141592654]

The truth is that car engines almost never wear out. They suffer either a catastrophic cooling or lubrication event (low coolant, low oil, excessive oil drain intervals, sludge buildup, detonation) or they have a metallurgy/gasket failure from too many thermal cycles.

 

If inertial forces were the largest then the aftermarket forged rod and piston people would be out of business. Stock internals can run at red line forever but increase the horsepower of an engine and they eventually break. Why, because the power stroke force overwhelms the rods and pistons. The inertial forces haven't changed.

 

Here's a FEM analysis of bearing load as a function of crank angle? I'll dispute your claim of inertial loads being the biggest.

 

[gathermewool]

Source? 4-stroke engine? Applicability?

 

I don't fully understand the crank angle X-axis. i'm going to need some more 'splainin....

 

p.s., what does this have to do with how crappy simulated gear shifts are!?

Edited May 3, 2019 by gathermewool

[DrD123]

I don't fully understand the crank angle X-axis. i'm going to need some more 'splainin....

4 cycle engine = 2 rotations of the crankshaft to complete all the cycles = 720 degrees.

 

I don't see any tribological data here. Only idealized hydrodynamic type data. Also - instantaneous is different than integrated, and higher rpm would bring with it increased temperature, etc. - it's not a simple system.

p.s., what does this have to do with how crappy simulated gear shifts are!?

nothing

[ripstik]

p.s., what does this have to do with how crappy simulated gear shifts are!?

[gathermewool]

4 cycle engine = 2 rotations of the crankshaft to complete all the cycles = 720 degrees.

 

I don't see any tribological data here. Only idealized hydrodynamic type data. Also - instantaneous is different than integrated, and higher rpm would bring with it increased temperature, etc. - it's not a simple system.

nothing

 

I caught on after I posted, but thank you for the clarification. The data curves are interesting, nonetheless. I haven't spent much time thinking about it, so I haven't matched up crank angle with cycle just yet.

 

Thanks!

[3p141592654]

I don't see any tribological data here. Only idealized hydrodynamic type data. Also - instantaneous is different than integrated, and higher rpm would bring with it increased temperature, etc. - it's not a simple system.

nothing

 

Indeed it is not simple. These simulations were done using AVL\Excite software and the elasto-hydrodynamic method. The bearings under study are from a turbo diesel and the study was focused on modeling wear from oil cavitation. Its a published SAE paper if you want to read more about it.

 

... now back to software shifts. Speaking of which, it is true that holding at peak HP is best for acceleration, but dithering +/- 1000 rpm of 4100 rpm peak probably won't have much affect since my seat of the pants says the horsepower peak is pretty broad on these engines. I cannot find a dyno plot for the FB25 anywhere to confirm.

[ripstik]

Indeed it is not simple. These simulations were done using AVL\Excite software and the elasto-hydrodynamic method. The bearings under study are from a turbo diesel and the study was focused on modeling wear from oil cavitation. Its a published SAE paper if you want to read more about it.

 

... now back to software shifts. Speaking of which, it is true that holding at peak HP is best for acceleration, but dithering +/- 1000 rpm of 4100 rpm peak probably won't have much affect since my seat of the pants says the horsepower peak is pretty broad on these engines. I cannot find a dyno plot for the FB25 anywhere to confirm.

 

it is true that the peak HP on these engines is more like crest of a soft hill HP, but the real issue with simulated shifts is not taking advantage of the best gear ratio you possibly could at any moment in time.

[ammcinnis]

Comic relief: I was at my local Subaru dealer's service department a couple of months ago. They were attending to a customer who reported that the transmission in her Gen 5 Outback must not be working correctly: She couldn't feel it shift. (True story.)