Optimum charge conditions for HV battery, Mk4 Jazz

[Kenneve]

Now, we know that the amount of charge given to a battery, by regeneration, is a function of Power (Kw) x Time (Hrs).
So, Given a suitable long downhill stretch of road and  appropriate traffic conditions & speed limits etc.
Is it better to descend the hill at speed, which assume higher charge rate, but shorter time, or, descend at a lower speed, which assumes lower charge rate, but for a longer time?
Does anyone know what the optimum speed should be?

I guess given a really long hill, we could completely charge the battery and regeneration would cease.

[Hicardo]

Hi, well I cant answer technically, but ive experienced what you describe many times, most recently in the yorkshire dales / moors last week.  the effect seems to be when the battery is fully charged and you are still going downhill in recharge mode, the engine revs will suddenly rise, as if the excess energy is being used up by the car 'shifting down'. I guess it has to go somewhere. told you it wasnt technical answer! 

[John Ratsey]

If you go faster then more of the potential energy will be consumed as drag losses. If you want to maximise regeneration going down a long hill then the challenge is to reach the top with the battery charge at the low end of its working range. If the battery happens to be at 70% when you start the descent then it will soon be full and you'll hear the engine wake up and run in braking mode (>3k revs judging by the sound) which means wasted energy, whereas if you started the descent at 30% charge then you can get moe than twice as much regeneration into the battery for re-use.

If you regularly visit the hill then you have the opportunity to experiment with the approach driving style so that the battery has low charge at the top. If the hill is up followed immediately by down then the charge is likely to be low but if you've got a flat section of road before the descent adjusting the approach speed (traffic permitting) so you run on battery may achieve the objective.

I'm wondering when Honda will store a digital terrain model in the vehicle and combine this with knowing which road is being used to predict the optimum battery operation. The technology is there and waiting to be used although it could get it wrong if there's a junction approaching. That would, however, get the battery operation right more often than the current situation of the vehicle not know if it's about to go up or down or along the level.

[Bristol_Crosstar]

Now, we know that the amount of charge given to a battery, by regeneration, is a function of Power (Kw) x Time (Hrs).
So, Given a suitable long downhill stretch of road and  appropriate traffic conditions & speed limits etc.
Is it better to descend the hill at speed, which assume higher charge rate, but shorter time, or, descend at a lower speed, which assumes lower charge rate, but for a longer time?
Does anyone know what the optimum speed should be?

I guess given a really long hill, we could completely charge the battery and regeneration would cease.

The main object is to minimise use of the brake, if you end up going too fast down a hill and have to hit the brake that energy is wasted.

There are steep hills around where I live and I regularly charge 100% going down them, the car has made some strange noises once the battery's full and the car is still going downhill, best to change back to 'D' if this happens.

[madasafish]

Theoretical calculations mean little in real world conditions..eg slow driver braking at every corner in front of you going down hill.Or junctions you MUST stop at. Or roundabouts or a herd of cows or horse riders....
(I travel a lot in the country.)

[Lord Voltermore]

The main object is to minimise use of the brake, if you end up going too fast down a hill and have to hit the brake that energy is wasted.

There are steep hills around where I live and I regularly charge 100% going down them, the car has made some strange noises once the battery's full and the car is still going downhill, best to change back to 'D' if this happens.

When a generator is charging it activates its electromagnets .These exert quite a bit of drag, hence a more powerful generator requires a more powerful engine to drive it. .  Regenerative  braking  makes use of the momentum of the car to help drive the generator. Even in D.  It saves fuel and the electromagnetic drag gives some 'engine braking'  . Using B increases the strength of the electromagnets, increasing drag, and  therefore engine braking  and charging the battery quicker.

But when the battery is fully charged  the electromagnets need to be switched off to prevent overcharging.  The car will no longer  have  'engine braking' and could surge ahead faster than before.   .  So , I believe , the     conventional brakes then compensate  by taking over extra  retardation duties, using its battery powered brake servo and advanced abs features.   Its this that makes the new noises. Some energy will be wasted until the battery can again take some regenerated charge.   

[culzean]

If the battery happens to be at 70% when you start the descent then it will soon be full and you'll hear the engine wake up and run in braking mode (>3k revs judging by the sound) which means wasted energy, whereas if you started the descent at 30% charge then you can get moe than twice as much regeneration into the battery for re-use.

This makes sense to use the engine as braking rather than overheat the conventional brakes and wear the parts out.. Those 'retarders' used on big lorries and coaches use the drag of an air compressor to slow down the vehicle...

[Hicardo]

'The main object is to minimise use of the brake, if you end up going too fast down a hill and have to hit the brake that energy is wasted'.....

Are you sure about that?  I thought that the first light press of the brake pedal has a regeneration effect, and that its not until you press brake pedal hard that it actually uses the friction pads?

[Mellorshark]

Correct. When I descend a nearby hill in B mode, slight brake pedal pressure increases regeneration.

[Kenneve]

Correct. When I descend a nearby hill in B mode, slight brake pedal pressure increases regeneration.

I don’t know how you can tell the difference between regeneration and friction braking in that situation.
Obviously overall braking effort will increase, but surely, only due to the additional friction braking.
I don’t see any indication of any increase in regeneration, unless I’m missing something.

[Bristol_Crosstar]

Correct. When I descend a nearby hill in B mode, slight brake pedal pressure increases regeneration.

I haven't seen this explanation anywhere in the owners handbook. Have you read it somewhere or is it just your opinion?

[culzean]

'The main object is to minimise use of the brake, if you end up going too fast down a hill and have to hit the brake that energy is wasted'.....

Are you sure about that?  I thought that the first light press of the brake pedal has a regeneration effect, and that its not until you press brake pedal hard that it actually uses the friction pads?

Shouldn't the system already be regenerating when it senses that the wheels are now driving the motor ?

[Kremmen]

I just let it get on with its stuff

[Pine]

My experience is of Toyota hybrids.  In their handbook and their tips for driving a hybrid it states that light braking increases regeneration.  On the dash one of the graphics you call view does show the amount of regeneration and with light braking it does increase.  The friction brakes only come into play with firm braking and at low speed to bring you to a complete halt.  The brake pads on a hybrid can last forever if driven gently. The only downside is that the discs can go rusty through lack of use.  When I leave home I go downhill to the main road, I usually knock it into neutral which stops the regeneration and makes the car use the friction brakes and that helps to keep them clean. 

[Lord Voltermore]

There is a limit to how much retardation is possible from regenerative braking alone  before it has to be supplemented by ordinary friction brakes.  Light application of brakes might stimulate the regenerative  effect to increase its contribution if and when it can .
  But unless there is still enough battery capacity to store the resultant free ,eco friendly energy, it is wasted. Or more precisely its not produced and  its a wasted opportunity . In a similar way that not utilising solar, wind, hydro electric, wave power etc   is wasted energy.   

Its  unavoidable unless you lug around a much heavier battery  99% of the time to capture a small amount 'wasted'   regenerative energy 1% of the time. (I made the figures up to illustrate the point -not factual)   

If  you need to  apply the footbrake hard or for any length of time  its likely  the friction brakes are used most.
 Which could be  a factor on a long descent ,such as a mountain pass, due to heat and brake fade.