Top speed and IMA

[mank]

Originally Posted by Tinytimmy80

I went to Berlin a couple of weeks ago and on my way back home I tried to keep up with some Polish criminals (pleonasm...) in their BMW 3 series.

HEY! I am of Polish descent and I resent that remark! LOL Just kidding! Actually that is kind of funny but I always thought it was Italian, Irish, German, Dutch, etc., etc, criminals!

[Tinytimmy80]

Yeah, you are right. It's just the running gag where I come from. In Germany as well.
The Polish people in my country always appear to be driving vehicles that are way too expensive for the kind of jobs they are doing.

I know the Dutch are renowned for drug trafficking and killing young blond American girls on small tropical islands , but keep driving very cheap cars .

[hessebauer]

yep; on our Polish borderline there are some signs (just another gag with a little bit trueness )
"Germans come around for vacation, your car´s are already there"

[Uriel]

Resurrecting an oldish thread here but just thought I'd mention some observed behaviour from my UK 2010 I2 ES.

Every day on my commute I go up a hill about 4km long with 100m rise (2.5 miles long 330 feet rise, althought the steepest part is the last mile) and a 70mph speed limit. The bottom of the hill is a roundabout so I'm usually effectively taking it from a standing start. The IMA charge almost always runs out and the car goes into regen before I hit the top unless I use a feather-footed drive with load technique. Most of the time I just head up at 65 to 70 mph though.

Just posting because I can avoid the forced uphill regen there so it may be relevant to top speed regen too.

Basically, if the car is in sport mode and I select 7th gear on the paddles while increasing throttle as necesary to maintain speed, it gradually stops assisting but does not regen until I either drop into a lower gear, switch to D, I lift off the gas pedal or the hills levels off. In 7th the car very gradually loses speed once the IMA assist drops off but 6th will maintain speed with a very slight regen.

I've seen the SOC indicator drop to zero using this technique but only when there's additional electrical load (headlights, radio, plus rear demister). Without the electrical load the SOC remains a little below half way after assist drops off.

Now in terms of overall fuel economy at the speed limit - assuming you do go into regen I think it's better to just let the IMA and CVT to do their thing when a regen occurs rather than manually over-riding. On that hill in normal mode at 70mph in regen the RPM on the tach sits somewhere over 3000 RPM. In Econ it goes to 4500 RPM. I think that's relevant because 4500 RPM is the peak torque of the ICE and therefore in it's most efficient range. What the car is doing is making the engine run at its most efficient and creaming off the excess to recharge the battery rapidly.

I suspect that the most fuel efficient way of tackling that particular hill is avoiding going into regen entirely, either by feather footing it and staying off assist as much as possible or by manually downshifting early so that more load is taken by the ICE earlier.

Going flat out at top speed - I'm assuming that you're already above the ICE's peak torque in the peak power range at 5000-6000 RPM. The CVT will already maxed out too and therefore can't compensate for the combined motor and engine power loss as it has nowhere to go. Without a fixed gear I think it'll do the same thing I see going up hill - regen yoyo! With the ICE and CVT both maxed out the ECU can't compensate for the parasitic IMA regen like it does on hills. I guess that means pretty much instant 14 BHP+ dropoff hence the lurching.