Unexpected lack of regen braking

[Harald]

I do live near the top of a hill - but we're not talking Zugspitz, it's about 1.5 km at 15% gradient, with the same again up the opposite side of the valley. When the car is (normally) fully charged, even B5 can't prevent it accelerating down the hill. But returning home with a depleted battery, B5 is more than sufficient to hold the speed (there's a 50 mph limit, so I can play with the regen settings to maintain the appropriate speed, and gain a mile or two of charge as well).

You might "simulate" a hill top loading function by loading in a time slot that is preset too short for reaching full capacity.

 

[ChrisMiller]

Thanks Harald. I don't have any problem, I've learnt to live with my little hill. There's no chance that the disc brakes won't be able to handle such a relatively short descent.

If I'm heading eastwards, I can run along the ridge for about 4 miles and only then have to descend. By that point, the battery has depleted sufficiently for almost full levels of regen braking to be available. And I can reach the bottom of the hill with almost the same range as when I left my house.

 

[Harald]

If I'm heading eastwards, I can run along the ridge for about 4 miles and only then have to descend. By that point, the battery has depleted sufficiently for almost full levels of regen braking to be available. And I can reach the bottom of the hill with almost the same range as when I left my house.

I just did a short calculation for the energy that can be harvested when driving down a 2000 kg vehicle for a 200 m altitude difference.
This is approx. 1 kWh and fits perfectly to your "almost full again" description after 4 miles along the ridge.

1000 meter in altitude difference can be sufficient for charging the battery by max. 50% of its capacity.

 

[ChrisMiller]

Thanks again, Harald! Not much chance of a 1,000 m descent in England

When I'm returning, I often go down the opposite side of the valley, and that adds 1 or 2 miles to the range indicator. If we assume 1.5 miles, that (at 3 miles/kWh) equates to 0.5 kWh. Which gives a reasonable efficiency of ~50% for regeneration.

 

[Hypermiler]

I don't think mine is necessarily related to stopping a charge. Yet I am also feeling my regen isn't working properly. Even with a pretty much empty battery I find it works to an extent to b3 but b4 and b5 don't seem to add anything. I really needed it on a steep descent with s trailer on ice today! Could it be anything to do with freezing temperatures?
Thanks

 

[Austen]

I do live near the top of a hill - but we're not talking Zugspitz, it's about 1.5 km at 15% gradient, with the same again up the opposite side of the valley. When the car is (normally) fully charged, even B5 can't prevent it accelerating down the hill. But returning home with a depleted battery, B5 is more than sufficient to hold the speed (there's a 50 mph limit, so I can play with the regen settings to maintain the appropriate speed, and gain a mile or two of charge as well).

Aren't you going uphill on the way home?

 

[ChrisMiller]

I do live near the top of a hill - but we're not talking Zugspitz, it's about 1.5 km at 15% gradient, with the same again up the opposite side of the valley.

 

[HHL]

I do live near the top of a hill - but we're not talking Zugspitz, it's about 1.5 km at 15% gradient, with the same again up the opposite side of the valley. When the car is (normally) fully charged, even B5 can't prevent it accelerating down the hill. But returning home with a depleted battery, B5 is more than sufficient to hold the speed (there's a 50 mph limit, so I can play with the regen settings to maintain the appropriate speed, and gain a mile or two of charge as well).

Actually... I just put the thing in B5 by flicking the gearshift back twice and then use the accelerator pedal to maintain speed... easier than fiddling with the paddles....................

 

[Harald]

Not sure if this has already been discussed:

If regeneration is set to less than B5, what happens if the brake pedal is used?
Does the car automatically increase regeneration as it logically should do?

Did anybody check this already by surveying OBD2 data?

 

[anko]

If regeneration is set to less than B5, what happens if the brake pedal is used?
Does the car automatically increase regeneration as it logically should do?

Yes, it does. But it does so in B5 as well. But in lower levels it does not do it to the same extend as it does in B5. This is why I have always said / claimed that, when moving along with normal traffic, B5 would be more efficient than B-less-than-5.

Now that my battery is deteriorating (which may be a result of frequent use of B5) B5 + brake pedal regen level is not as much as it used to be. As if it is throttled in order to prevent further damage to the battery. These days I don't see much difference between various levels anymore. At least, not once the brake pedal is applied.

Did anybody check this already by surveying OBD2 data?

Hitting the brakes first increases regen level and only when that is not sufficient it applies the friction brakes. I know this from monitoring pressure in brake lines via OBD.

 

[Harald]

Hi Anko,

thanks for the quick answer.

As per my understanding, I would expect 1 of 2 different approaches:
Either 1)
Brake pedal does not start regeneration at all. Regen delivers only as per the preset value B0-B5 when the foot is taken of the gas pedal.
Or 2)
Brake pedal starts regeneration and uses regen up to the max., doing the rest needed by the friction brakes.

It seems not logical to me that using the brake pedal initiates regeneration but not up to full level?
In case that you should have metering data that quantifies the effect, it would be great if you can share it.

Best regards, Harald

 

[greendwarf]

Hi Anko,

thanks for the quick answer.

As per my understanding, I would expect 1 of 2 different approaches:
Either 1)
Brake pedal does not start regeneration at all. Regen delivers only as per the preset value B0-B5 when the foot is taken of the gas pedal.
Or 2)
Brake pedal starts regeneration and uses regen up to the max., doing the rest needed by the friction brakes.

It seems not logical to me that using the brake pedal initiates regeneration but not up to full level?
In case that you should have metering data that quantifies the effect, it would be great if you can share it.



Best regards, Harald

Surely option !. is never going to be engineered into an automatic hybrid, as the whole point of regen is to recover energy from braking. With an automatic this would be lost under option 1. if drivers use a "left foot" braking technique.

 

[anko]

It seems not logical to me that using the brake pedal initiates regeneration but not up to full level?
In case that you should have metering data that quantifies the effect, it would be great if you can share it.

Unless the engineers realised that frequent heavy regen, like quick charging, could be bad for the battery? And they just failed to warn us about it?

 

[Harald]

Hi Anko,

As you have shown very nice graphs from your data recordings in other threads, I was just curious if we all could learn about this behaviour from real data.

I guess I still will use B5 as standard braking device because it hardly makes sense otherwise to drive a PHEV up and down the hills.

Best regards, Harald

 

[maby]

.....

Did anybody check this already by surveying OBD2 data?

Hitting the brakes first increases regen level and only when that is not sufficient it applies the friction brakes. I know this from monitoring pressure in brake lines via OBD.

Are you suggesting that the point at which the car switches from regen to friction braking is dynamically controlled by the car's electronics? I had always assumed that it was rather similar to the Toyota system - the brake pedal includes an intentional inch or so of free travel before it begins to make contact with the piston of the brake cylinder and there is an electrical sensor measuring that travel and controlling the regen levels. I'm not very fond of a pure "brake-by-wire" system - a Citroen that I owned many years ago almost killed me when the engine failed on a long downhill, resulting in a loss of pressure in the hydraulic system and a complete loss of braking!

 

[anko]

Are you suggesting that the point at which the car switches from regen to friction braking is dynamically controlled by the car's electronics?

No, I think that whether or not friction brakes are applied depends on far you depress the brake pedal. But I also think that how far you depress the brake pedal may depend on the amount of regen braking available. So, to a certain extend that brain of the car does have a say in it by controlling how much regen braking is available.

 

[anko]

As you have shown very nice graphs from your data recordings in other threads, I was just curious if we all could learn about this behaviour from real data.

I guess so. EvBatMon and PHEV Watch Dog should both be able to display such information. EvBatMon may allow you to add it yourself. With PHEV Watch Dog you depend on Daniel to have it added.

 

[Harald]

I guess so. EvBatMon and PHEV Watch Dog should both be able to display such information. EvBatMon may allow you to add it yourself. With PHEV Watch Dog you depend on Daniel to have it added.

Thanks. Maybe I will install one of these apps later.

Best regards, Harald