Optimum conditions for best HV battery charge.

[Kenneve]

Have been trying to assess the best conditions, to achieve max charge in the HV battery.
Consider a long downhill slope, running in ‘B’ mode.
Is it best to:-
Run downhill at best speed to achieve best charge rate? (Assuming higher speed = higher Amps)
Or
Run slower down the hill to allow more Time, for charging and subsequently achieve a better overall rate?

There is a very good video on the Internet, which shows how the e-HEV works mechanically, but there seems to be not much available, that shows how it works electrically.
My own view is, slower Is better, although I can’t prove it!

[John Ratsey]

Any hill that is long enough and where you need to use the brakes to stop the car gaining excessive speed will get the battery to 100% after which engine braking is activated. It's the excess gravitational force (potential energy) above that needed to overcome friction and aerodynamic drag which will be used to charge the battery. The amount of excess energy depends on the gradient and vehicle speed: The higher the speed then the more of the energy is absorbed in keeping the car moving.

[nowster]

Just drive normally in B.

Pretty much whatever you do (apart from putting it in neutral and coasting, or doing a ton down the hill) will charge the battery.

Feathering the brake pedal will also initially use some regen braking until the battery can't take any more.

[Bristol_Crosstar]

I have found it best to drive in D mode and then use B to slow down where possible instead of using the break pedal other than in stop-start situations like traffic queues where B mode is best. If in B all the time then the accelerator will be pressed more if you slow down where you don't need to so not necessarily the most efficient way to drive. Pressing the brake pedal wastes energy, regen only occurs when neither the brake or accelerator are being pressed.

[Kenneve]

Understand all that has been said.
I was just trying to work out how best to secure the best regeneration, out of a given hill.
I assume there is a limit to the current rate, the battery will accept, hence whether descending slow of fast is best.
For example, whether descending with a regeneration current of 60 amps for 2 minutes, is better than 100 amps for 1 minute?
Or maybe I’m just looking for problems that don’t exist?

[ColinB]

I hope this is a purely theoretical question that you don’t intend to put into practice. Our roads really don’t need people driving with their attention on the ammeter in order to deliberately drive fast or slow chasing some kind of ideal regeneration condition. So, speaking as the driver who might be in front of you or following you down that hill, I’d prefer that you drive according to the road and traffic conditions.

[John Ratsey]

I was just trying to work out how best to secure the best regeneration, out of a given hill.
I assume there is a limit to the current rate, the battery will accept, hence whether descending slow of fast is best.
For example, whether descending with a regeneration current of 60 amps for 2 minutes, is better than 100 amps for 1 minute?

A lower charge rate is better for the lithium chemistry and there must be a limit but even if this is half the maximum discharge rate (which provides a lot of power) it's quite high. It's jamming on the brakes at 70mph which is likely to overload the battery.

Your other challenge is to reach the start of the descent with a fairly low charge level in the battery.

[culzean]

I hope this is a purely theoretical question that you don’t intend to put into practice. Our roads really don’t need people driving with their attention on the ammeter in order to deliberately drive fast or slow chasing some kind of ideal regeneration condition. So, speaking as the driver who might be in front of you or following you down that hill, I’d prefer that you drive according to the road and traffic conditions.

Yup, far too many distractions being introduced into vehicles,  the only place you should be looking when driving is at the road in front and a quick glance at speedo and in mirrors frequently.

[Kenneve]

I hope this is a purely theoretical question that you don’t intend to put into practice.

Yes it is, I'm not quite that daft!

[Kremmen]

Initially I'm going to be in "D" because my most frequent journey is through smart motorway roadworks and I use cruise to stop me drifting over the average limit.

I'll monitor the charge level whilst stuck at 50mph for 20 miles or so. The sensors will no doubt kick in the ICE when needed which should indicate what they think is the charge level when the ICE temporarily shuts down.

[nowster]

Pressing the brake pedal wastes energy, regen only occurs when neither the brake or accelerator are being pressed.

That's not correct. If you're driving downhill on the limiter with your foot on the accelerator, regen will kick in.

If you're lightly pressing the brake pedal, regen is used rather than the brakes if it provides enough deceleration (and the battery can take the charge).

I drive in B around town and in D on highways. It takes a little while to get used to driving in B, as the right pedal controls desired speed, not acceleration.

[John Ratsey]

I'll monitor the charge level whilst stuck at 50mph for 20 miles or so. The sensors will no doubt kick in the ICE when needed which should indicate what they think is the charge level when the ICE temporarily shuts down.

I think you'll find what happens on a level road is: (i) car runs on engine in direct drive with some charge going to battery until the charge level reaches 70% (7 bars on battery gauge); then (ii) car switches to EV mode until the battery charge drops to 3 bars on gauge; then repeat from (i). However, hills will cause this pattern to vary including power from battery supplementing engine power in direct drive for going uphill and switching to EV mode when going downhill.

[Kenneve]

I think you'll find what happens on a level road is: (i) car runs on engine in direct drive with some charge going to battery until the charge level reaches 70% (7 bars on battery gauge); then (ii) car switches to EV mode until the battery charge drops to 3 bars on gauge; then repeat from (i). However, hills will cause this pattern to vary including power from battery supplementing engine power in direct drive for going uphill and switching to EV mode when going downhill.

I agree with all that John says here.
However with regard to the accelerator position, I believe regen will start as soon as you lift off the accelerator and the use of the footbrake makes no difference to the regen effect, in fact using the footbrake means less kinetic energy is available for regen.
I use mainly 'B' mode, which is almost like one pedal motoring in most conditions, using the brake only when coming to a stop.

[John Ratsey]

in fact using the footbrake means less kinetic energy is available for regen.

Pressing the brake pedal is a signal to the car that it needs to slow down and this will first be acted on by increasing regeneration with the brakes used only if the generator and/or battery can't handle the power. However, it's possible that, for safety reasons, there is a direct linkage between pedal and brakes but will only be active if the pedal is pushed hard.

I use mainly 'B' mode, which is almost like one pedal motoring in most conditions, using the brake only when coming to a stop.

That's the way I now drive although I spent the first few months rarely using B.