But you’re probably using a significant amount of engine braking (which in this context, is the same as friction braking) on your 7 mile drive if you don’t touch the brake pedal. You’re not really coasting unless you put it in neutral.
If you truly coast (i.e. put the car in neutral) you’ll find, at least on the flat, you’ll need about half a mile to stop from 30 mph (and at such a slow deceleration, you’ll aggravate anyone behind you). Even my humble Honda Civic will coast seemingly forever if you put it into neutral and don’t mind how long it takes to stop (or how long you’re spending doing half the speed limit).
All fun and games :-)
I don’t take it to extremes or get in anyone’s way really, I just try to use the brakes as little as possible.
Engine braking… yes ok… but does an EV ever truly freewheel when not regenerating?
It depends on what the car designers wanted.
Taycan can be set up to behave like a ‘normal’ car and coast.
Tesla, not really, the closest is ‘creep’ + regen on ‘low’ which is a bit like an automatic car forced into a slightly lower gear.
Graham wrote:
does an EV ever truly freewheel when not regenerating
I don’t see why not. Brushless motors tend to feel very ‘notchy’ if you turn them by hand, but as you pass each notch you get out nearly the same energy as you put in. There will be some losses in eddy currents, but compared to all the work you need to do to spin an IC motor, it’s pretty minimal.
I laughed aloud when I read that the Victorians used regenerative braking, after a fashion. The London Underground is built such that as trains approach a station, they climb a slope to slow them down. Then they set off downhill again.
kwlf wrote:
The London Underground is built such that as trains approach a station, they climb a slope to slow them down. Then they set off downhill again.
Stockholm underground (first built in the 1950s) does, too. I believe that’s SOP for underground design.
40 or 50 years ago Lucas electric vehicles were using regenerative braking on Bedford vans and an Ogilvy designed taxi. You took your foot off the accelerator, the vehicle began to brake and at the same time the energy of the forward motion was sent to regenerate/recharge the battery. Back then, and I don’t think the principles have changed greatly, you only used battery energy when you depressed the acclerator and you didn’t really need brakes unless of course you had not taken your foot of the accelerator early enough. A bit like using or not needing to use the brakes when landing an aircraft.
I once drove (40 to 50 years ago) in a convoy of Lucas electric vehicles from Birmingham to London, down the M1.
It was a long time ago and not a great deal has changed with regards to the functioning of electric vehicles. I still think that Lucas got it about right.
Cobalt wrote:
Steve6443 wrote:The latest Mercedes A250e models have a system where you can, in e-mode, adjust the amount of regeneration going on, from very little – ie coasting when you take your foot off the gas right up to single pedal operation – foot off the gas, it starts recuperating energy.
Does it then use regen when you use the brake pedal moderately (like the Taycan), or does it convert brakepads to heat (like the Tesla)?
To explain the system – you can use the steering wheel paddles on the A250e, in electric mode, to set the level of recuperation – so you can either have single pedal mode – foot off the gas, it slows down immediately or normal operation – foot off the gas and it coasts or something in between; the system has 4 or 5 distinct settings covering how much it will recharge when you take your foot off the gas. Apart from that, the system I believe is identical to that in my E300de which means that when the car needs to slow down, the generator, which is part of the gearbox, is engaged and draws current to charge the battery, which then creates the drag to slow the car. Apparently there is a clutch of some sorts involved.
As far as I’m aware, the car uses mainly this generator to create engine braking within the drive train – I’m not sure whether it is actually using the brake pads at all….
Graham wrote:
I don’t take it to extremes or get in anyone’s way really, I just try to use the brakes as little as possible.Engine braking… yes ok… but does an EV ever truly freewheel when not regenerating?
It must do, the energy must go somewhere.
I did a little experiment last night on my late-night trip home. Just coasting in neutral, from 60 mph, I was still going 20 mph almost a mile (1.6km) later – any normal driving you would maintain 60 till near the junction and would absolutely require braking of some sort so as to not aggravate every other driver behind you. If an electric car slows quicker than this when you take your foot off, the energy must be going somewhere, at least into a resistor bank. (A truly coasting electric car would probably be doing 30 mph a mile later, just because they weigh so much more than a petrol car, and have so much more kinetic energy as a consequence). (Trains for decades have had “dynamic brakes”, where the traction motors are used to brake – in the past they just dumped the power into a resistor bank, today – at least for electric trains – they are often regenerative. This isn’t new technology by any stretch of the imagination).
Regenerative braking for electric cars doesn’t involve extra weight of consequence – code doesn’t weigh anything (well, not that we can measure) and the additional power transistors won’t weigh much.
By the way, the Police suggest you do use the brake pedal. Engine braking gives no indication to drivers behind that you’re slowing – it’s good practise to press the brake pedal enough to turn on the brake lights even if you don’t intend to actually use more than engine braking.
alioth wrote:
Engine braking gives no indication to drivers behind that you’re slowing
Just to avoid any misunderstanding here – EVs do turn on the brake lights when regenerative braking is used, even if the brake pedal is not touched.
alioth wrote:
I did a little experiment last night on my late-night trip home. Just coasting in neutral, from 60 mph, I was still going 20 mph almost a mile (1.6km) later – any normal driving you would maintain 60 till near the junction and would absolutely require braking of some sort so as to not aggravate every other driver behind you. If an electric car slows quicker than this when you take your foot off, the energy must be going somewhere, at least into a resistor bank. (A truly coasting electric car would probably be doing 30 mph a mile later, just because they weigh so much more than a petrol car, and have so much more kinetic energy as a consequence). (Trains for decades have had “dynamic brakes”, where the traction motors are used to brake – in the past they just dumped the power into a resistor bank, today – at least for electric trains – they are often regenerative. This isn’t new technology by any stretch of the imagination).
Sure. I’m not saying I never use the brake pedal, just not very much. The drive I described in an earlier post is a 6-7 mile stretch of A-road with varying 50 and 60mph limits. Unless there is some traffic issue, I don’t brake from one end of it to the other – and I cover it more quickly that the average vehicle, no-one is waiting behind me. It’s just a case of having your speed right for the bends and not having to jump on the brakes, although a willingness to corner faster helps. It’s no coincidence that I can’t remember the last time I had to replace pads (let alone discs), but for many these are standard items at the annual service.
Agree the technology is not new at all, and for an EV is now trivial to implement in terms of any weight or complexity penalty. It’s not on ICE vehicles (much) because what’s recoverable does not justify the weight and complexity.
Cobalt wrote:
Just to avoid any misunderstanding here – EVs do turn on the brake lights when regenerative braking is used, even if the brake pedal is not touched.
That is probably useful if they are regenerating ‘hard’ with the vehicle slowing fairly rapidly, but potentially liable to mis-inform drivers behind if it happens during a deceleration akin to coasting? The purpose of brake lamps has never been to indicate that a vehicle is slowing down, but to indicate that the driver is applying the brakes.
alioth wrote:
By the way, the Police suggest you do use the brake pedal. Engine braking gives no indication to drivers behind that you’re slowing – it’s good practise to press the brake pedal enough to turn on the brake lights even if you don’t intend to actually use more than engine braking.
The Police in this country suggest a lot of things and I rarely consider them a source of wisdom. There are plenty of reasons not to ride the brakes.
