There's a maximum power that the EV can regenerate to the battery. In my (10-year old design) Zoe it's only about 40 kW, so not much more than a third of the maximum tractive power. Going downhill, you can get away with just regen up to that power, and then you have to use the friction brake as well. Because power is speed times torque (~ tractive effort), that means for any gradient there is a maximum speed that you can descend without wasting energy in the friction brake, and the steeper the hill the slower that speed is. On a very steep hill that can be quite slow but on most hills you don't need the brake.
The not so good bit is that regen is limited when the battery is nearly full and when the weather is cold, so sometimes you don't get back the energy you expect.
Yes, the dash display tells you how much power (+ve) or regen (-ve) you are running at. But going down hill, if you come right off the accelerator in "B" mode (1-pedal mode) and the car is still gaining speed you are too fast for regen, so you have to slow down on the friction brake and try again! Or just accept that you are "wasting" energy!
It's a system and you have to analyze it, to figure out the best behavior.
If you regen brake to a too-low speed, it actually costs more battery energy for field excitation, than is made back in regenerated energy. And that establishes when the car switches from regen to friction braking.
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There are a couple projects, that transfer overburden from the top of a mountain (strip mine), to a lower elevation. In this application, the BEV dump truck has net energy output, and the truck actually transfers some of the battery energy into the grid, to make room for more regeneration on the next trip. I think I've read of two projects that are doing this (net output, never needs charging). The truck drives up the mountain empty (does not use as much power), and drives down the hill with the regen running, and a hundred tons of dirt in the back (potential energy).
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If the truck was instead hauling materials out of a deep hole in the ground, then it would need a lot of recharging at the end of the trip, to prepare for the next trip. They don't seem to write quite as many articles about that case.
Well, every little bit helps as one supermarket advert states. I would imagine that during the design of brakes such things would be borne in mind, but there will always be those who through habit drive on their brakes, After all you can use gears and the engine to slow down a petrol car, I'm told. Maybe the brakes are not directly controlled, and are part of the speed management system and are used intelligently as needed by the apparent need. Brian
Depends. On mine in its "B" mode, the closest it gets to 1-pedal driving, coming off the accelerator gives pretty much full regen; the brake pedal is needed only for friction braking. Driven well (or rather for least wastage) the brake pedal is only used to bring to a final halt and hold at rest.
I would never drive like that. If you move your foot off the pedal temporarily to cater for scratching your ankle, you suddenly slow down quite rapidly. Also it makes more sense to me to have one pedal to mean go faster and one to mean go slower. I'd set it for no pedal pressing to provide a small amount of power to keep up with wind resistance.
But given the option, many do prefer it. I've driven petrol and diesel for near 50 years but it took a day to decide I preferred the hi-regen mode! Other EV drivers I have asked appear to like it too.
I guess it could be the same as my habits with the steering wheel. I use one hand, and find it easier and safer. If you need to turn sharp left to avoid something, with two hands your brain has to send two opposite instructions to your arms, one up one down. But with one hand it's a single instructions. Faster and easier. Also, provided you have power steering, one hand is many times faster in tight spaces when parking etc. Watching someone shuffle the wheel and take half an hour to park is hilarious. Oh but it's in their precious highway code.
I see some folk using their brakes every few seconds. Going along the motorway in a queue of traffic, they seem to want to be precisely a certain distance behind the car in front, with no leeway whatsoever. Speed up a bit, slow down a bit, I'd love to see their mpg. Probably a member of the Institute of Advanced Motorists (aka wheel shufflers). I had a colleague in that stupid group, he believed he should drive at the speed limit at all times, because that's why it's there. Never above, never below, including corners.
In an automatic, you can very easily slow down rapidly, just select 1st gear. It will drop as soon as possible through all the gears. Just don't do it in a 1988 Range Rover, or you will get first, immediately, and with catastrophic effects.
The same pedal will control the two types of braking. It will probably be programmed to use the regen braking to the maximum of its capability at that instant, and to supplement with friction braking if regen on its own is insufficient - ie if the driver presses the pedal further indicating that regen isn't sufficient. Hopefully the transition between the two is seamless (I'm guessing on that - I've never driven an electric car).
The amount of reg braking available will depend on speed and other factors: the faster the car is going, the more braking force is available. So at low speeds, on a steep downhill or in emergency, probably most/all of the braking will be frictional.
I would imagine there is a limiting regen force that is controlled by the cars ECU, to avoid overheating the battery by very rapid charging or the "waste heat dissipation" resistor unit.
Have a drive of one and play - they're fun to drive!
Regen braking is power limited, mostly by the electronics and the battery, but clearly also it cannot exceed the drive power by much because it's the same motor/generator doing both. Power is force times speed, so regen braking is _less_ effective at speed and gets greater as you slow down (more speed = less force for the same power). Until you get used to it, slowing down for a junction, you get the feeling that you won't quite stop in time on regen, but it tightens up as you slow down until about walking pace when you need to use the friction brake.
Similarly, for any given hill, there is a _maximum_ speed which will get you down on just regen, any faster and you need the footbrake as well.
Amount of regen is limited by battery temperature and state of charge. On a cold winter morning with a full battery you get very little; on a hot summer day with the battery half full you get a lot (maybe 12 kW and 35 kW on mine).
As to how they blend, that's a matter of manufacturer's choice and user options. Mine can't use friction on the accelerator, only regen. On the brake pedal it can use both. The type of blend depends on user options.
Some Teslas now have the option to blend limited friction brake on the accelerator pedal as well. That's to give a consistent one-pedal drive experience; when it's cold or the battery is full it blends in some friction brake to make it feel the same as normal regen.
Maybe I will, if I can do it with a straight face. I intend to keep my diesel car for as long as I can, because electric cars have not yet progressed to the state that can provide the same usability, in terms of range and (even more important) refuelling time. I mostly do short journeys in my car, which would ideally suit an electric car, but I want a car that at a moment's notice can drive a long way, in one go (apart from a brief loo stop). I don't want to have to make an enforced stop for an hour or so to get me enough range to complete my journey, and I don't want to have to search for a recharging station. When I don't have to plan a longer journey like a military exercise, factoring in recharge stops when travelling around on a day out, then I might buy one. My diesel is 15 years old and has done
190,000 miles. I'm hoping I can keep it going for a lot longer, and more importantly we can keep my wife's newer diesel going even longer, and just accept that when my cars dies and has to be replaced with an electric, we can manage on just the one car (hers) that is free of the range/recharge restrictions.
I do wonder how the country's electrical infrastructure is going to cope after 2030 when no new IC cars are sold and gradually more and more electricity is needed for electric cars. Will the HV and mains wiring cope, and will we have enough generating capacity, especially at night when there's no solar, to charge cars overnight. Overnight charging can be done at a lower rate because within reason you don't mind how long it takes as long as you can rely 100% on your car being full for the drive to work in the morning.
I imagine generation profiles will change: instead of a large demand during the day, a "cooking surge" in the early evening and little demand overnight, it will probably become more constant, with some charging demand as everyone gets to work and charges for the journey home again, and then a huge increase in demand at 7 PM or thereabouts as everyone gets home from work, puts their cars "to bed", on charge, and the intelligent charging algorithms manage the demand so as to level it out throughout the night.
Intuitively, it "feels" counter-intuitive that braking force decreases as speed increases. I presume this means that you use your friction brakes most at high speed (for times when you need to slow down quickly) and at very slow speed. Maybe braking force is proportional to speed as long as you allow the power to increase without any limit. I can understand braking force being limited artificially by the rate at which you can dissipate the heat.
Did you find that you adjusted fairly quickly to regen braking on the accelerator - does it "feel" the same as the retardation you'd get in an IC car when you lifted off the power, or do you find you need to keep your foot on the accelerator in situations where you'd be able to lift off in an IC car for a brief break (break. not brake!) during level or slight descent?
I wish manufacturers hadn't made (some) electric cars with one-pedal driving. I like to have one pedal that controls power, with limited, predictable retardation due to friction and air resistance, and a totally separate pedal that controls braking (whether it be frictional or regen). I like to be able to lift my foot right off the accelerator at times such as a very gentle downhill, and not have to keep my foot permanently on the accelerator to avoid regeneration.
I've just bought a ride-on mower and I still haven't got used to its single-pedal operation: the engine runs at a constant speed and the forward and backward pedals control the hydraulic transmission. But as soon as you come off the pedal, the thing stops very quickly. I still find myself instinctive pressing the brake (left-foot on the mower); for me, left-foot braking is easier to get used to (though something I would NEVER do in an automatic car) than single-pedal braking.
Well at the moment you are in luck, because most if not all EVs have some sort of option to make them feel more like an ICE car. Although I think Tesla on some recent cars may have moved away from that.
But the point is that EVs (and hybrids) are different, they can recover kinetic energy and to maximise that recovery it's necessary to drive them slightly differently. Newer ones are probably better, but on mine that means thinking ahead and starting to slow down earlier. Having all regen on the accelerator and having friction come on only with the brake pedal is just what you need for immediate feedback that you are doing it properly: if you have to touch the brake pedal before you are almost at rest you have failed!
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