One pedal driving not necessarily efficient?

Brake regen has been on BMWs for over 10 years (2010 for F01 7 Series) to recharge the 12V battery.

The best way is clearly the left hand paddle braking like the Koreans do. That way you can achieve ultimate efficiency and save another polar bear.

 

This is just lazy writing and generalization.

 

Most efficient to least efficient:

• coasting
• regen
• braking

If you're decent at controlling your momentum and coasting to red lights, that's the way to go. To come to a stop at the same red light with regen braking, you need to spend more energy up front, and then the regen braking only harvests a portion of it back. That's a lot better than friction brakes turning it all into heat, but it's worse than not spending that extra energy up front in the first place.

I think that's why Porsche is doing the pedal-activated regen braking described in the article... let the car more efficiently coast until the driver says "hey, I need to get rid of more kinetic energy" with their foot. It makes a lot of sense.

 

I’m not sure what you mean by this.

 

What that means is if you coast under the speed limit, you must use les feux de détresse de son véhicule or risk a $100+ fine per SAAQ.

 

Lol ok.

I can only infer that — using the SE as a model — the coasting driver puts the needle at zero a few hundred metres before the regenerating driver goes to zero and below. But in the SE, “coasting” with the needle at zero decelerates the car at an incredibly slow rate. That’s virtually unuseable in any urban and suburban environment. Also — as you allude to — if we are going to be doing math, then time should be part of the equation as well: in order to cover the same distance in the same amount of time, the “coasting” driver would need to bring their car up to a higher velocity in order to get to point B at the same time, thus using more energy, not less.

 

OPD certainly increases the chances of unindented micro regen braking.

Regen in blended brakes can only handle 0.3 G or so. So, on the flip side you could accidentally friction brake instead of regen. Probably inconsequential, but..

Ultimately pure friction brakes just feel so much better than blended brakes. One exception is the Ford Lightning. The blended brake feels totally normal, probably due to their existing customer base demanding no science project weirdness in work trucks.

 

Lol science project weirdness! Great line

 

I remember the days of hypermiling on ICE and regretting not filling up before the $0.30/gal price hike. If ONLY I had more empty space in the fuel tank...grrrrrr. Can't wait for the snow to melt off the solar panels in the spring!

 

I, for one, like the regen feature. My first stop was rather sudden, but in a couple of blocks, my foot had the trick. But, I used to downshift to slow down (or keep a constant speed when going downhill). Now, I don't think about breaking. (I also gave up worrying about brake lights and the driver behind me.)

 

Meaning, if coasting takes you from point A to point B, regen braking will take you from point A to some point well short of point B ... more energy is needed up front to get you all the way to point B (the red light, in my analogy). And time doesn't really factor into it very much when it comes to things like red lights; whatever is saved by getting there quicker will be spent by waiting longer.

It's not some drastic hyper-miler thing, either. Who doesn't take their foot off the accelerator early when approaching a red light you know isn't going to change by the time you get there? (EV drivers who want to actually get to the light, I guess.)

The only times regen braking is a net positive (from an energy perspective) are when it 1) replaces friction braking, or 2) when it harvests energy from the effect of gravity (descending a hill). That's also why the Cooper SE's freeway behavior annoys me so much; don't regen brake if I tick the cruise control down a little, just coast to the new speed.

 

The SE's high regenerative braking is 0.19g, low regenerative braking is 0.11g. I don't know what max is for friction brakes, but I know from experience combined with high regenerative braking it's much higher than 0.19g.

 

The 0.3 figure I think came from what the article said the Porsche’s regen was capable of… which is pretty aggressive, and makes their claim that it covers ”the vast majority” of braking scenarios seem perfectly reasonable.

 

I think I'll take the SE for what it is, as long as I don't have to do a premature reduction gearbox oil change and multiple HV battery coolant flushes like the Korean EVs. If it means I have to gently feather in some throttle while adjusting cruise control because of permanent magnets in the electric motors, then so be it.

 

I didn’t mean A to B quicker. The SE coasts down so slowly that coasting is almost useless — if not impossible — in most urban and suburban driving situations. But let’s assume you’re cruising down some six-lane suburban stroad between Best Buy and Home Depot on a Monday at 10:30 am and the lights are a mile apart. You’ll need to get up to speed quicker if you want to coast down before the next light, while I accelerate more slowly and decelerate gradually while the needle dips below zero. Anyway, whatever, without empirical evidence one way or the other I’m willing to bet the difference between them is likely negligible. In good weather I’m able to get 145 miles on a charge driving my way, which is without worrying about coasting or ultimate efficiency. Yes, the car is green and saves me money and I feel good about that, but above all else it’s able to be clean and green and save me money while also being a total blast to drive.

 

Imagine what they'd say about a manual transmission

 

The stoplight is just one example for simple illustrative purposes, but there are a lot of other situations... approaching slower traffic up ahead, taking a long-ish freeway offramp, etc. I coast all the time in my Cooper S, and that coasts down much slower than the SE does.

Ok, but the question was whether 1-pedal driving is the most efficient way of driving. And unless the laws of physics have been suspended, harvesting kinetic energy back into a battery is always going to put less back than was spent to provide the kinetic energy in the first place. Coasting has losses due to friction (mechanical friction, rolling resistance, air resistance, etc.)... regen braking has those same friction losses PLUS the losses inherent in the regen process. That was the entire point the red light example was intended to convey. Again, much better than throwing all that energy away in heat with traditional brakes, but still less efficient than coasting by itself.

And if you insist upon actual empirical evidence... well, here are a couple resources that peg regen braking efficiency at around 70%-80% (not quite "negligible"):
https://www.sae.org/publications/technical-papers/content/2013-01-2872/
https://dspace.ups.edu.ec/bitstream/123456789/20506/1/UPS-CT009183.pdf

 

I drove an auto petrol jaguar yesterday. It had approximately zero engine braking. That was unsettling at first.
I love the SE one pedal driving around town. For highway use, I try to avoid it. I did a crude regen braking test a few weeks ago up a mountain. Total regen efficiency was 75% . For every kWh I put into my cars speed or height, I regen about 0.75kWh back into the battery. Way better than friction brakes, but not as good as coasting. Regen braking is a lot easier to modulate outside sport mode.

 

Assuming the same wheel-bearings are on both cars, wouldn't the heavier SE with its more efficient tires coast down slower than a Cooper S? Of course, it requires a sensitive ankle to induce coasting in the SE, but I believe it would coast further than a Cooper S. It's too bad Bimmercode can't enable the programming of a coasting button.