T i m wrote:
On 06 Jun 2021 21:16:30 +0100 (BST), Theo
wrote:
I think gen2 Prius regen goes down to about 7-8mph.

That's lower than I thought but that said, I know all too well how
'heavy' a shorted electric motor can become when trying to push a
mobility scooter. ;-)

OTOH 1+ tonne of car has a lot of KE, even at low speeds. A 20hp motor
isn't a lot in comparison.

At that point the
amount of braking you can get from the motor alone is limited, and you want
it to stop accurately (going 1 metre extra across a pedestrian crossing
would not be great).

So it *will* actually bring you to a halt with motor braking alone,
noticeable above rolling resistance etc?

It won't let you find that out, it brings in the friction below 7mph.

So what does it do when descending hills, assuming you approach the
top of one with a fully charged battery? Two questions really:

Does it 'coast' if you don't touch the brake like a car in neutral or
'hang' on the motor / transmission like one in gear but with you foot
off the throttle?

I think it's like a regular auto - it won't brake unless you press the brake
pedal. It's not one-pedal driving like some EVs. It's not 'coasting' in
the sense of running away due to having the clutch disengaged (the
transmission is always engaged - I suppose you could try forcing it into
neutral but it would complain mightily). If you take your foot off the
accelerator then it's a fight between friction, gravity and momentum as in
any other car.

What if you apply some (electric) brake that would maintain the same
speed but then make the battery fully charged (either really or
technically), does it then apply the mechanical brakes on it's own
(like an ABS) 'instead' or start coasting faster till you use
mechanical brakes?

When the battery is full it'll use friction brakes. You can't select what
kind of braking it uses, you can only tell by paying close attention to the
sounds and the feel. You just use 'the brakes' and it decides how to
achieve it.

There is also 'B' mode which provides classical engine braking, in case
you're doing a heavy descent and are worried about your friction brakes
overheating. I've used it about twice, in neither case did I need it.

The motors on the mobility scooters we have seem quite large (by
comparison then) and the big one will bring it and me to a halt from
full speed (8mph) down a fairly steep slope in a bit over a second.
;-)

I imagine you don't weigh a tonne? :-)

Theo