Regenerative braking - performance (torque\deceleration) variation

Howdie fellas, idrive my i3 in Atlanta and love it (being a 4- Quandrant drives-motors engineer myself). :shock:

I've noticed that sometimes , possible at higher speeds or after all-out acceleration, the regenerative braking performance is sluggish and not the maximum I usually get .

This happens at all discharge levels so the battery can theoretically take the charge. I simply release the "gas paddle" but don't get the full deceleration\brake power although the charge pointer goes to full brake.

This happens in Atlanta so temperature cant be the cause.

Thoughts?
Thx in advance!
H

Regen is affected by temperature but you've ruled that out. It's also limited when near full SOC and you've ruled that out. The regen is also limited to 50kW due to temperature restrictions within the Infineon six-pulse IGBT chipset within the EME.

Probably not a factor, but if you have/are going over bumps, the car limits the amount of regen during that time and for a short delay afterwards.

A recent software update reportedly reduced the maximum regen power at higher speeds with the regen power gradually increasing as the speed decreases. But this effect likely always occurs, not just sometimes.

janner said:

Regen is affected by temperature but you've ruled that out. It's also limited when near full SOC and you've ruled that out. The regen is also limited to 50kW due to temperature restrictions within the Infineon six-pulse IGBT chipset within the EME.

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Thx Janner! The temp.restriction sounds plausible as I might have chased the temp.up during acceleration (Max IGBT load >> 50kW) and then the subsequent braking is limited.

Thank ya'll! H

jadnashuanh said:

Probably not a factor, but if you have/are going over bumps, the car limits the amount of regen during that time and for a short delay afterwards.

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I must say that I have found this and have relied on the regen going down a hill to retard my speed only to have the car go over a bump and pick up speed unexpectedly ! Not a nice experience

I have since noticed that it is sensitive to steering angle/ sideways G load. So when going down a hill with an bend in it if you are using the regen to retard your speed the act of turning sharply to negotiate the bend will also make you pick up speed when you do not expect it making you likely to overlook the corner and want to dab the brakes mid corner.

Mito said:

jadnashuanh said:

Probably not a factor, but if you have/are going over bumps, the car limits the amount of regen during that time and for a short delay afterwards.

Click to expand...

I must say that I have found this and have relied on the regen going down a hill to retard my speed only to have the car go over a bump and pick up speed unexpectedly ! Not a nice experience

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It's probably better than having the tires freewheel, then be subjected to the potentially severe shock of having a wheel spinning way above the road speed of the vehicle! BMW did try to limit that in software during one of the firmware updates, but there are still limits. One always needs to be ready to use the actual brakes on these cars when trying to slow.

I don't know your location or what tyres you use, but it is a known fact in Norway, that when using winter tyres with soft rubber, the i3 senses this movement in the tyres and reacts as if there is a little slippery road and hence reduce the regen. I had my i3 delivered with Nokian winter tyres, and noticed a big difference in regen from the i3 demo car tested with Bridgestone wintertyres. Now on summer tyres with harder rubber, the full regen is back.

autowinder said:

I don't know your location or what tyres you use, but it is a known fact in Norway, that when using winter tyres with soft rubber, the i3 senses this movement in the tyres and reacts as if there is a little slippery road and hence reduce the regen. I had my i3 delivered with Nokian winter tyres, and noticed a big difference in regen from the i3 demo car tested with Bridgestone wintertyres. Now on summer tyres with harder rubber, the full regen is back.

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I live in Sunny Georgia / Atlanta but THX for the Insight ... H