CVT's (non-hybrid) = fewer opportunities for fuel-cut mode (DFCO) when coasting?
 

https://ecomodder.com/forum/attachme...1&d=1476368139

The last CVT I spent much time driving was the 1.2L, 3-cylinder Mirage pictured above.

I was genuinely impressed by how much it was programmed to pursue fuel economy: It tries its little heart out to keep cruising revs as low as possible (see chart).

I remembered being pleasantly surprised that...

That has me wondering: do CVT's programmed for such low RPM, fuel-saving operation offer fewer chances for zero fuel burn (DFCO) when releasing the throttle and coasting in gear? Seems possible you might only get a brief fuel cut before injection resumed to keep the engine running.

Other types of transmissions would have the engine at a higher RPM for a given road speed at the start of coasting. So, more time in fuel cut-off mode.

If that's the case, a CVT hypermiler might benefit from more neutral coasting.

Splitting hairs? Probably! These are the things that keep me awake at night.

Funny you should mention this. I noticed shortly after buying the Versa with the CVT I never saw any indication it ever goes into DFCO. My Ultra Gauge sometimes on downhill coasts will give me readings of 175-200 MPG but even then it's constantly changing with speed and rpm. The only possible indication is in the factory installed MPG unit. It will go to 99.9 but the Ultra Gauge is just showing that it has exceeded its limits. The Scan Gauge in my Ford Escort wagon with 5 speed manual will go to 9999 as soon as I let off the gas at highway speed and stay there until either I accelerate again or the engine needs fuel to continue to operate.

With problems that have plagued the CVT I refuse to shift from "D" to "N" and back to "D" to save a couple drops of gas. If it did cause any problems with the CVT it certainly wouldn't be worth the $4000-$5000. they want to replace one.

Doesn't seem so right that a CVT could harm the DFCO ability.

Longevity could be the motivation behind this. Which is not to say a CVT could not be built that would last virtually forever with DFCO, but rather that it's added wear to the one component most likely to send a car to a junkyard, and people are cost-sensitive both at purchase and during repairs.

2018 Honda CRV
 

Same experience as "2016 Versa"...I have a ScanGage. Immediately upon lifting my foot from the accelerator, it goes into DFCO for about 1/2 second. Then the CVT adjusts and eliminates DFCO. I am trying the EonC just for fun. Can't say it's helping enough to measure. Still getting 29-30 mpg calculated.

Another thing I forgot to mention in my previous post the owners manual for the Versa strongly urges coming to a complete stop before shifting gears. As best as I remember the CV transmission in the Versa is non towable.

2018 Honda CRV
 

Only time to be dead stopped is to shift between R and D (probably in and out of P as well). Can't flat tow the CRV at any time. Towing behind an RV can be done with the front wheel drive using a car dolly. Flat bed tow truck is the only way to tow the all wheel drive.

Edited towing...

I watched the Ultra Gauge this morning as the car would coast down hills on the way to church. Even at higher speeds than I had the c/c set and in a full coast the best GPH reading I saw was something like .23 on a warm engine. Nowhere even close to .00.

I'm sure the my 15 Rogue does if the hill big enough. It will ramp up the rpm when in a coast and it starts picking up speed. It doesn't do it very often because most of the hills we normally aren't big enough. But one neighboring town main street is down hills both was with the low spot in the middle and is steep enough it does it every time in a 20 mph zone if I crest the hill at that speed.

Had 4 tanks when in Colorado around at 35 mpg, it's been a while but I think the CVT would ramp up to either 3400 or 4300 rpm going down hills to avoid brake use. Car's ahead of me were braking a lot more than I seemed to need to.

From my personal anecdotal perspective, my wife is a decent eco-driver, though certainly not as obsessed with it as I am. She manages in the high 30's and low 40's consistently with her CVT Honda Fit. So while a CVT might be less effective in the hands of a dedicated eco-driver, perhaps in the hands of someone who is merely trying to do well without extricating every last tenth of an MPG, it serves them better than a "normal" transmission would.

Also of note, my dad is decidedly not an eco-driver. I watched him consistently slip my Yaris (manual transmission) out of gear to decelerate and use only the brakes. For someone like him that doesn't utilize DFCO at all, a CVT's lack of it would have no noticeable effect on his fuel economy, and with its optimized shifting and torque distribution map might help him achieve higher numbers.

Since it tends to keep the engine at a steady RPM more often, it seems to be an improvement on that matter.

This is all good info - thanks for the CVT anecdotes.


Versa: your car uses the same JATCO CVT-7 transmission as in the Mirage I drove. Though it could be programmed differently for different applications (1.6L 109 HP vs 1.2L 78 hp).


Considering pretty much the only reason for building CVT's is improved fuel economy, it sure is odd that they don't do DFCO as much as other transmission types.

I wonder if it's partly because there aren't enough DFCO opportunities built into the various fuel economy test "routes" (driving patterns).


Rooster: your experience of seeing "boosted" RPM when going downhill is interesting. Do you mean RPM goes up higher than you'd see for example with a fixed gear connection to the wheels (like a manual) as speed increases?

Yes RPM's go way higher than would on level ground. It's normally just under 2,000 rpm at 55-60. I probably wasn't going over 70 mph down hill but reving a whole lot more, I'd crank up the AC to create more engine braking/load.

The in town spot it does it every time, I'm rolling along at 20-25 mph, it's basically idling, it will go up to 13-500 rpm to keep from picking up speed.

The Navigation does know the speed limit most of the time but I don't think it uses it to control the engine braking. I think it just sense of increase of speed with no throttle input and decides you don't want to pick up speed.

Not sure if it will do it when Cruise control is enabled (95% of time), it blinks a little warning light when exceeding the set point but don't think it's ever slowed it down. You can set a warning set point at 5 or what ever MPH above speed limit in the Nav so I don't know if it's using that same limit for that alarm. It's on the dash not the Nav screen. I turned the audio alarm in the Nav on once at 5 over, wife let me know after her first drive to turn it off.

Odd. That's anti-eco! CVT's are weird.

That is weird.

Are there statistics showing how much better fuel economy a CVT achieves than a standard automatic?

When I bought my Mazda in 2015 I remember reading that they chose to stick with a conventional automatic design instead of a CVT for a couple of reasons, but I don't remember if fuel economy was in there.

FWIW, my Insight surely does DFCO on deceleration. It will even mildly regenerate, more so at higher speed. (it will regenerate harder if I press the brake pedal)
It will stay in DFCO if I feather the throttle to neutralize regeneration and prolong the 'glide'.
Regeneration aside, I see no reason why DFCO would not function in non-hybrid CVTs?

Unless you're running AC. That may keep the juice flowing even when decelerating.
The less I use the ventilation system and other power consumers, the better it DFCOs.

Oh yeah, it's a big difference over an older slushbox design.

Here's a telling apples-to-apples comparison that 2016 Versa will appreciate:

For a couple of years, Nissan took the unusual step of offering 3 different transmission choices in the Versa sedan, all with the same HR16DE 109 hp 1.6L engine & as in the Versa Note hatchback:

EG. for 2013...

• 4-speed automatic (w/lock-up torque converter) = 26 city / 35 hwy / 30 combined
• 5-speed manual = 27 city / 35 hwy / 30 combined
• CVT = 31 city / 40 hwy / 35 combined

https://fueleconomy.gov/feg/bymodel/...an_Versa.shtml


(Of course, ecodriving the 5-speed, you would still match or beat the CVT numbers in the same real world conditions. No pulse & glide shenannigans required: just upshifting to the highest gear as soon as practical, and with smart use of neutral coasting and DFCO.)

I haven't driven the Elantra (6 spd auto) a lot, I drove it 2 days to work just to see how it compares to the Cobalt. Running with Cruise on, it would down shift going down hills to avoid over running the cruise set point. 49 mpg calculated, 53.7 indicated on a short tank.

On the 15 Rogue the Eco button is normally pushed, seems to only deaden throttle input though.

The Versa on downhill coasts also increases the RPM's by several hundred but in just over 1 year of driving the car with and without a/c use and on some pretty long steep hills I've never seen the Ultra Gauge indicate DFCO. There's pretty significant engine braking, just the opposite of what I want it to do. I read somewhere that there was a way to go into the ECU and make adjustments to the amount of engine braking. There were 3 different settings but only 1 was recommended by Nissan. I suspect maybe one either has minimal engine braking or none at all, one has moderate engine braking and one is probably like they have it set from the factory. I'd thought about trying to find someone who could go into the ECU and make the changes but again with the problems Nissan has had with their CVT's I decided maybe that wasn't the best choice.

Metro MPG-My '16 Versa has an EPA rating of 31 city, 39 highway, and 34 combined. I don't remember the automatic and standard transmission numbers but, I do remember the CVT has the best ratings. As you can see from my fuel log I can easily beat the highway EPA rating with probably somewhere between 80-90% of my driving being on rural 2 and 4 lane roads with speeds in the 45-55 MPH range. If all my driving were city I'm not even sure I could maintain the 31 MPG rating. According to the Ultra Gauge this car doesn't care for extremely low speeds. It seems that right around 45 MPH may be the sweet spot. Since I'm usually in no hurry to get to my destination a large portion of my driving on secondary roads is around 45 MPH and on the better roads 50 MPH. With the c/c set at 50 MPH on flat sections of the highway even this time of year when the temps are cooler I can sometimes maintain MPG numbers in 60-70 MPG range for up to a mile or more.

Sure the usually wider gear-spread on a CVT compared to a more traditional AT or MT might also be accountable for the MPG improvements.

that is garbage for a versa 1.6l back in the day the 2006 sentras were getting about 30-32 for the 1.8l

31mpg highway with a 6.0L v8 engine


only doing about 23mpg in the city though not too bad considering a normal 6.0l can barely get 11MPG/14MPG(Suburban 1500 with 6.0L)

DFCO comes into play to get that.. these 6.0L are way more efficient then the L76 :) since the Highway mode will be 100% ICE

40-45MPH = 40-45MPG with the EVT transmission.. considering the engine is barely moving at 1,000-1100 RPM in v4 mode not too bad for 3.0L displacement...


i'm sure this "special mode that it falls into" might be able to get higher then 48mph by improving the Aero dynamics...(mpg falls and it switches to normal mode) so 38 to 45mph is the sweet spot

Fuelly says: 27.5 MPG average for the 2006 Sentra, 72 vehicles, 1+ million miles.


31.1 MPG average for the Versa Note (2014-2019)



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Obviously, hybrids are designed to maximize engine-off coasting & DFCO. Not really what this thread is about. Maybe I should have specified in the title that we're talking about "belt & pulley type" non-hybrid vehicle transmissions -- I'll clarify that.



Having said that, the older belt & pulley style CVT in my dad's '09 Civic does pretty aggressive DFCO.

I'm sure that has a large impact. My brother had an '08 Versa with a 6 speed manual transmission and I think 1.8L engine that he bought new. Just from riding in the car with him a few times I could see that it had really short gearing. As I remember at somewhere around 55-60 MPH in 6th gear his engine was still at over 3,000 RPM. At the time I think I remember him making a comment to me that he was only getting in the low 30's per gallon. At 50MPH if I recall correctly my Versa with CVT is running somewhere between 1400-1500 RPM on flat highway.

it's not even a real hybrid that is just marketing "hype"

I might be able to go between 0 and 60 feet before the ICE starts
it's just an aggressive "Auto Stop" system at best.....


remember this battery is 10 years old with less then 15% capacity left.. about 200wh of 1.8kwh..

as a real hybrid will let you run at pretty much any speed with the electric motor it's capped at 29mph not even fast enough to drive in a Metro area(as the limit is 35)

Still apples and oranges.

The same applies to the Brazilian version of the Toyota Yaris.

I have a 2018 Forester. My ScanGauge II shows zero L/100K when coasting with a warm engine. The LOD shows 75-80 percent when accelerating at 20 percent throttle, and I can drive all day without going over 1,500 RPM. Most city driving at 40-60 KPH has the engine at 1,000-1,200 RPM. On the highway, 100 KPH is still just 1,200 RPM.

I drive a 2017 Honda Civic with a CVT, I haven't done any measurements with ODB2 or something like that. I just made various tests by resetting the bordcomputer and driving the same track sections for a few times. I couldn't notice any differences in fuel consumption by going into neutral. So I don't think it helps saving gas on such a relatively modern CVT.

Wow: 100KPH / 62MPH at 1200RPM is amazing for a gasoline engine.

That's in heavy diesel truck territory.

Here you can watch how relatively low the RPMs are with a CVT of the 1,5 liter Civic at different velocities.
Still I think the RPMs would be slightly lower with a manual transmission in the same car:

https://youtu.be/F1dXjiuT6JM

Thanks for that video. The Civic was achieving 88KPH at about 1500RPM and those proportions were roughly the same at other speeds but with some variation.

This about what I see with my Mazda3 automatic: 55MPH (88KPH) at 1530RPM.

However, the Forester cited above was making 100KPH at 1200RPM, which is amazing to me.

correction
 

Correction: 1,800-2,000 RPM at 100 KPH -- I was in a hurry and had 60 KPH on my mind when I wrote that.

The Forester's CVT seems to always have the engine in the 50-80 percent LOD range, and you can get 99 percent LOD at 30 percent throttle. I accelerate at 17-20 percent throttle and that usually gives 60-70 percent LOD.

What's interesting is that LPH does not vary between D or N when stopped. Turning the AC on will increase it 30-40 percent at idle.

I installed Subaru rain guards on all the doors and keep the windows cracked 1-2 cm on the highway. This gives ample air flow through the cabin with zero buffeting or wind noise. I only use the AC when the humidex is impossible.

OK alcom, thanks for that.

Darn, I was hoping the Forester's CVT enabled the lower RPMs as earlier reported. I have always been a fan of slow-turning engines to reduce internal friction and increase longevity and efficiency, but I guess it was too much.

Oh well, c'est la vie.

There's a sweet spot in LOD for maximum efficiency, and Subaru's CVT has its eye on that. The engine has variable valve timing, but 1,800 RPM is still near the bottom of the torque curve.

I've been limiting my highway speed to 90 KPH whenever possible. We used to do that in the 70's, and it's time to have a good, hard look at it again. No matter what your rig, your fuel efficiency goes up by 30 percent compared to 120 KPH.

I agree with the speed limit reduction point!

However, the oil-production war currently going on between Saudi Arabia and Russia is sinking the price of oil and thus its products. This makes it more difficult to get the general public behind any idea of reducing speed llimits to reduce consumption.

Alas, my 50-year-old son-in-law showed me Saturday night his brand new 2020 Ford Mustang...a GP something-or-other. It features a 760HP V8 that makes 17 MPG on the highway. I attribute it to his mid-life crisis. I doubt he drives any slower in his new ride.

He showed me his new car not long after I was complimenting my Mazda3 on its highway mileage potential.

In two years of big city (Toronto) driving, the Forester has averaged 10.5 L/100KM or 22 MPG. On a long highway drive at 90 KPH I can consistently get 7.0 L/100KM or 33 MPG. That's from fuel and odometer records, using Fuelio for Android.

My ScanGauge II is so accurate, when I fill up the pump shows within 0.1 L of what the ScanGauge had predicted. When ScanGauge upgraded their circuit board a few years ago, they sent me the new board with install instructions for about $15. That's very good for customer loyalty. I have a custom gauge (ScanGauge gives you the code) for transmission temperature (TFT), so I can monitor the CVT temperature. I have BlueDriver for diagnostics, but nothing can replace the ScanGauge for everyday real-time feedback.

I agree. The ScanGauge is a magnificent tool, and its management has a reputation for being very customer-oriented. I've been using a ScanGauge for a few years now, and it has paid for itself and then some by helping me achieve significantly better fuel economy.

I recently read that a competitor product with a larger and more modern-looking screen and readout was having problems, and some users report fading screens that could no longer be read. My old ScanGauge keeps right on working as good as ever.

1800RPM @ 85mph 136KPH V4 mode 4 speed auto

(technically it's a inline v4 since it's bank 1 only)

I did a controlled run to map RPM against speed -- 100 kph on the expressway going out and 40 and 60 kph on city streets coming back -- light traffic, roads visibly flat no strong wind. Here's what I found.

Forester CTV -- 40 km x2 on cruise control
100 kph 1750-1800 rpm - expressway, going out
40 kph 1250-1350 rpm - city streets, coming back
60 kph 1250-1500 rpm - city streets, coming back

The bottom end for the CVT is just 500 rpm above idle. The wider variance at 60 kph is likely due to variations in road pitch. Engine torque curve is a factor. Even with variable valve timing, the sweet spot is likely 1500-2500 rpm. Maintaining momentum and keeping airspeed (i.e. resistance) down are at least as important as low rpm. The CVT will deliver lowest rpm for torque needs.