Why is e-pedal so detrimental to efficiency?

[ztev]

I understand that you lose efficiency every time you engage the friction brake; however, according to Nissan, e-pedal will (supposedly) only engage the friction brake near the end to bring you to a complete stop. When driving, I do my best to regulate the accelerator that I coast whenever possible.

I much prefer the convenience and experience of e-pedal; however, last night I decided to try driving without it, in D mode after reading other people's reported efficiencies of around 4mi/kwh or more. I've always struggled to consistently reach 4, and typically get 3.5 or below. Last night though, a short trip resulted in an average of 4.7! I was shocked! Outside temp was about 55F, and I didn't run any climate control. Similar conditions with e-pedal usually result in at least an entire mile less per kwh, which seems insane.

Maybe I'm just not as good at coasting as I thought?

 

[LeftieBiker]

Welcome. e-Pedal does make coasting very difficult, because you have to carefully modulate the braking effect with your foot. I think that most people use the mode for stop & go driving, and one of the other modes for more continuous driving. Those who do use e-Pedal or B mode on the highway put a lot of effort into feathering that accelerator pedal...

 

[frontrangeleaf]

Not a fan of e-pedal. It's not a feature that fills some unmet need for me.

Our son loved it for a while, then got tired of it too.

I think it's oversold. We use D mostly now. Occasionally B in heavy traffic. If they dropped the e-pedal feature, I'd never miss it.

-b

 

[GerryAZ]

I rarely use e-pedal because it seems to use friction brakes (and flash brake lights) more than I want in my typical driving conditions. That is probably why I too get lower efficiency when using it. I thought it sounded interesting and was looking forward to using it while I was waiting for the 2019 to be delivered, but soon found that I did not care for it. I usually just use B-mode (wish I could set B-mode as default for one pull of the shifter). I do sometimes use e-pedal in really heavy stop/go driving because it saves moving foot back and forth from accelerator to brake.

 

[GRA]

While I've never driven a LEAF which offered e-pedal, I've driven a Bolt which offered D and B (B mode is one-pedal driving), plus extra regen on a paddle mounted on the steering column usable in either mode. As others have noted, I found B mode was best for surface streets with lots of traffic/signals/lights, or else heavy freeway stop-and-go, also driving very fast on tight two-lanes, and roads with very steep descents. I used D with paddle as needed the rest of the time, and was able to maximize efficiency. I really liked the Bolt's mode options, as it made it easy to coast a lot and regen only when needed, and it seems like the LEAF could use something similar.

 

[alozzy]

I haven't driven a Hyundai EV nor a newer LEAF, but the regen paddles behind the steering wheel in an Ioniq seem like an excellent solution to me. I'd rather be able to select among 5 levels of regen vs e-pedal and D/B/ECO.

 

[Stanton]

So are you guys saying that e-pedal is yet another thing I don't miss on my Gen1 Leaf vs Gen2?

 

[LeftieBiker]

So are you guys saying that e-pedal is yet another thing I don't miss on my Gen1 Leaf vs Gen2?

That probably depends on whether or not you have to drive in heavy traffic often. You probably also don't miss your car getting somewhat hysterical when you try to back up past other cars, kids toys, or suspicious-looking flaws in the pavement.

 

[Marktm]

So are you guys saying that e-pedal is yet another thing I don't miss on my Gen1 Leaf vs Gen2?

Putting 20,000+ miles on Gen 1 2012 and almost 7000 miles on Gen 2 2021, I'm definitely a fan of e-pedal for around the town driving of all types. It took a while of learning to "feather", but won't go back. Similarly, it took lots of "learning" to use ProPilot effectively on the 90 mile trip to my cabin - mostly highway at 65 mph, but will always use it - but without e-pedal due to hard breaking when off cruise!

Using e-pedal, I consistently get 4.4+ m/kWh, but admittedly have not made a real effort to compare with any other mode.

Very encouraged that the "cabin" trips netted 4.12 m/kWh and 3.93 m/kWh recently - which results in completing the round trip without a charge should be possible for some time.

 

[fester]

"e-pedel" is a novelty, but for me that's pretty much it. "eco-mode D" is still my go to, and years of letting off the accelerator and moving to the brake are hard wired.

 

[LeftieBiker]

"e-pedel" is a novelty, but for me that's pretty much it. "eco-mode D" is still my go to, and years of letting off the accelerator and moving to the brake are hard wired.

Likewise. I've used e-Pedal just enough to be able to use it without it feeling horribly wrong, but I don't think I've used it in over 6 months.

 

[GerryAZ]

So are you guys saying that e-pedal is yet another thing I don't miss on my Gen1 Leaf vs Gen2?

I would gladly trade the e-pedal of the 2019 for the adjustable headlights of the 2011. There were several features on the 2011 that I missed with the 2015, but the 2019 has everything I missed on the 2011 except the adjustable headlights and the little marker lights on the front fenders (although it does have turn signals in the edges of the mirrors).

 

[knightmb]

"e-pedel" is a novelty, but for me that's pretty much it. "eco-mode D" is still my go to, and years of letting off the accelerator and moving to the brake are hard wired.

Likewise. I've used e-Pedal just enough to be able to use it without it feeling horribly wrong, but I don't think I've used it in over 6 months.

Same way. First time I used it, I was thinking "ok, neat" but after that I couldn't find any situation to actually use it except for bumper-to-bumper traffic where you are moving at 5mph with constant starts and stop. That was until I figured out the Leaf could do that automatically with the intelligent cruise option, required no foot work then. :lol:

I've relegated ePedal to "beginner mode" for teaching my kids how to drive for now.

 

[HerdingElectrons]

50k miles & 3.5 years of ownership & I have extensively tried all the mode combinations for months at a time & 99% of the time I use B mode & Eco off and I avg 4.4 year round. I also wish B mode had a persistence setting like e-pedal but oh well.

Another byproduct of a legacy automaker presumably that hasn't felt the need the need to to provide after purchase QoL updates.

B mode keeps the friction brakes out of the question until you physically touch the pedal & requires less pedal modulation on freeway off ramps for example to keep the regen from maxing out & using friction brakes so I like that a lot.

 

[denwood]

50k miles & 3.5 years of ownership & I have extensively tried all the mode combinations for months at a time & 99% of the time I use B mode & Eco off and I avg 4.4 year round. I also wish B mode had a persistence setting like e-pedal but oh well.

Another byproduct of a legacy automaker presumably that hasn't felt the need the need to to provide after purchase QoL updates.

B mode keeps the friction brakes out of the question until you physically touch the pedal & requires less pedal modulation on freeway off ramps for example to keep the regen from maxing out & using friction brakes so I like that a lot.

Maxing regen (happens more often in ePedal mode due to higher regen rates) is likely the reason you'll do better in B or D.

 

[Bouldergramp]

The first thing I do after pushing START it flip e-pedal on. Not my wife...she won't even try anything new.

 

[LeftieBiker]

The first thing I do after pushing START it flip e-pedal on. Not my wife...she won't even try anything new.

You can set it to remain on until turned off, but I'm guessing that this is an issue with your wife?

 

[glenngroves]

No process is 100% efficient. When you speed up (using electricity of course) then use regen to slow down, you only regenerate some of the electricity that was used to speed up, so to speak. The only figure I have heard on this, is that regen regenerates 20% to 30% of the electricity. I don’t know if that is accurate or not, but it does at least make clear that there are losses in the process.

Regenerative braking is more efficient than physical braking; physical braking regenerates 0% of the electricity of course. But simply staying at the preferred speed is more efficient - loses less energy - than regen braking followed by accelerating to get back up to speed again. So unless you have to slow down, it is more efficient to stay at speed, than to slow down using regen and then speed up again.

ePedal is very convenient, I use it around town and I love it; but it does mean that unless we get the accelerator pedal perfect all the time, we will sometimes be using regen to slow down, and then using electricity to speed up again, which is less efficient than just coasting, or staying at the preferred speed. Hence when turning ePedal off we get better range per kWh.

ePedal is for comfort or convenience, not efficiency, a bit like heating and cooling are for comfort or convenience, and actually a little detrimental to efficiency.

 

[k9spud]

unless we get the accelerator pedal perfect all the time, we will sometimes be using regen to slow down, and then using electricity to speed up again, which is less efficient than just coasting, or staying at the preferred speed. Hence when turning ePedal off we get better range per kWh.

I've noticed on my 2013 Leaf in B-mode (haven't really used D-mode to know if it does the same), I seem to get energy savings by turning on cruise control to maintain current speed when compared to trying to maintain current speed with the accelerator pedal, no matter how hard I try to hold the pedal "just right."

I wish the car's computer would've been a bit smarter in this regard and make it possible to maintain speed with the accelerator pedal while getting just as much efficiency as cruise control. They could have made it have some slight buffer range where the pedal doesn't cause that regen/speed up cycle if you're holding it mostly steady.

 

[alozzy]

Any amount of regen results in considerable losses...

An EV's motor is at best 80% efficient at converting electrical energy to mechanical output at the drive shaft. Then, there are some losses in the gear box too.

When regen kicks in, the EV motor becomes a generator, converting mechanical energy at the drive shaft back to electrical energy stored in the pack. However, most EV motors aren't as efficient at acting as a generator vs a motor.

In a perfect system, regen recovered energy would be the power originally drawn from the pack times the square of the motor's efficiency.

So, assuming perfectly symmetrical efficiency (unlikely), if 10 kWh of energy is drawn from the pack to accelerate a vehicle from 0 to 30 mph, then regen would at best put back 10 * 0.64 = 6.4 kWh back into the pack when decelerating from 30 mph to 0 mph.

But, EV motor's efficiency isn't linear at all speed either. Then there are the gearbox losses to consider...

I would guess that if you can get 50% regen efficiency average (so 70% motor and gearbox efficiency combined), that's pretty good.

I've had conversations with people who swear that they can go up a hill and come back down again and end their trip with "almost the same pack SOC". It's laughable that they think that's even close to possible.

Note that with cruise control, the car will do regen on downhill sections or when slowing down with adaptive cruise. If you want higher efficiency, you need to learn to coast in neutral at the right times. Doing that can definitely beat cruise control on longer trips, unless the highway is dead flat and you never change speed. Coasting downhill is super efficient, unless you go so fast that increased air drag cancels any gains.