Brake energy regeneration?

V

Visionist

Member
Is this only for 2013+ cars with start-stop or do all E89s have them? How does it work? Obviously there's no electric drive motor for gathering surplus energy during braking so...?
 
I believe that the the alternator is only used to generate electricity during engine braking and is decoupled when the throttle is open
 
PerryGunn said:
I believe that the the alternator is only used to generate electricity during engine braking and is decoupled when the throttle is open
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Surely that can't be right? On a long motorway journey of several hundred miles you would end up with a flat battery if that were true!
 
Firstly, all vehicles with efficient dynamics have it, it does not just apply to start stop engines. Efficient dynamics can be any number of specific items which help with efficiency of the car. My 2009 E88 had brake regeneration, was auto with no stop start and the E89s are all listed as efficient dynamic vehicles. Efficient Dynamics was introduced to vehicles from March 2007, any new or facelifited models after this date had efficient dynamic technology as standard.

You may find this page of interest to actually gauge what efficient dynamics is all about. http://www.bmw.com/com/en/insights/technology/efficient_dynamics/phase_2/introduction.html

And here is the official line on brake regenration

With Brake Energy Regeneration, BMW EfficientDynamics points the way to a more energy-efficient future. As soon as you brake or take your foot off the accelerator, the kinetic energy is captured and fed to the battery. This reduces the amount of power the battery takes from the engine and hence lowers fuel consumption. When the driver presses the accelerator, on the other hand, the alternator is decoupled from the drivetrain. With fewer components drawing power from the drivetrain, more of the engine's output can go into accelerating the car.
 
I put a plug in voltmeter into cigar socket and haven't seen much change in the voltage output.
Probably why a new battery needs coding. The alternater charging circuit needs to know a nominal level, when it drops the alternator kicks in as required. So it tries not to charge when batteries full and chooses deceleration as a opportunity to charge the battery. If not a lot of braking, then it just applies a top up charge as required.
Probably how they get the battery to last 5 odd years (or at least through the warranty period!) rather than 2 odd with standard battery.
 
So pretty useful technology for increasing battery life then, cool :)

Still, you'd think BMW would crow on about a five year battery more than a 3% increase in touring range, it's a more impressive feat...

At least the car still has conventional hydraulic brakes and none of the problems with brake feel regenerative hybrid setups have. How do the brakes feel on the E89? Quite a bit of pedal travel? Easy to modulate at different speeds?
 
Can I ask what you currently drive? Apart from a Type R civic for 16 months, I've always driven bmws so the brakes seem as responsive as I expect. To be honest, the brakes are very quick and can stop the car pretty quickly in dry conditions. They have a good feel to them and apply just enough but if you step on them, they'll bring you to a stop very quickly.
 
Currently I'm car-less, and if circumstances fail to become favourable, I'll be hard pressed to afford to run a 35i or even any half-decent car for the foreseeable future... :driving:

Now THERE'S an incentive to get my ar$e in gear ahahha
 
Visionist said:
How do the brakes feel on the E89? Quite a bit of pedal travel? Easy to modulate at different speeds?
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The E89 brakes are very good and progressive. It is easy to get just the degree of braking you require and there is no huge amount of travel before they bite - they are just right.

I have had 6 BMW's and all have had flawless brakes.

When I drove BMW's at work as a Traffic Policeman they had immense punishment at times but never suffered fade or warped discs. The braking efficiency of them was second to none. When we have cars tested to see if they are up to our use many fail unless a manufacturer fits uprated brake discs and pads. The BMW's all pass on standard setups. A few years back we apparently tested a Subaru Impreza turbo. It failed the test as we effectively set fire to the standard brakes. That doesn't happen on BMW's !
 
Visionist said:
Currently I'm car-less, and if circumstances fail to become favourable, I'll be hard pressed to afford to run a 35i or even any half-decent car for the foreseeable future... :driving:

Now THERE'S an incentive to get my ar$e in gear ahahha
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what makes you ask about brake regeneration then? Most cars do this.
 
SO8 said:
Visionist said:
How do the brakes feel on the E89? Quite a bit of pedal travel? Easy to modulate at different speeds?
Click to expand...

The E89 brakes are very good and progressive. It is easy to get just the degree of braking you require and there is no huge amount of travel before they bite - they are just right.

I have had 6 BMW's and all have had flawless brakes.

When I drove BMW's at work as a Traffic Policeman they had immense punishment at times but never suffered fade or warped discs. The braking efficiency of them was second to none. When we have cars tested to see if they are up to our use many fail unless a manufacturer fits uprated brake discs and pads. The BMW's all pass on standard setups. A few years back we apparently tested a Subaru Impreza turbo. It failed the test as we effectively set fire to the standard brakes. That doesn't happen on BMW's !
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thats intersting , as time and time again i read how rubbish bmw brakes are, that the calipers are only single pot , that they fade etc etc but i have never had an issue on the 3m or the 4m, a good balance beteen good braking and wear and noise imo, the only thing i find sometimes ,is if i brake a little quickly they feel overbraked on the initial top of the pedal making for a harsh first bite. :driving:
 
flybobbie said:
I put a plug in voltmeter into cigar socket and haven't seen much change in the voltage output.
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I wouldn't expect to see much change at the cigar lighter as it needs a constant output.
 
Angie4m said:
With Brake Energy Regeneration, BMW EfficientDynamics points the way to a more energy-efficient future. As soon as you brake or take your foot off the accelerator, the kinetic energy is captured and fed to the battery. This reduces the amount of power the battery takes from the engine and hence lowers fuel consumption. When the driver presses the accelerator, on the other hand, the alternator is decoupled from the drivetrain. With fewer components drawing power from the drivetrain, more of the engine's output can go into accelerating the car.
Click to expand...

One must remember that words from the marketing department are not necessarily reality, just their interpretation or understanding of an engineers explanation. So I wonder if the alternator is physically decoupled from the engine or just decoupled from the battery on a no load cycle as this would be so much less complicated.
 
Battery voltage is 12.2 (measured) engine not running.
Cigar lighter socket varied from 14.5- 14.7 volts after a few seconds and only when engine running. Need to check on a good run, then down hill with engine braking.Probably so as to not let us run stuff and flatten battery and all the problems that would create. Don't think there is anything special about the voltage regulation.
All they have to do is on deceleration either detect that the throttle position is closed, ie engine braking, or use the fuel overun cut signal to switch on alternator if the system detects a drop in volts.

I think a bit of licence has been used in the term 'Brake energy regeneration'. Might be so on a electric vehicle where a motor could become a generator.
I would have called it 'Engine braking energy recovery'.
So whats the gain in mpg.
I suppose for 2.5 litre engine they are quite economical.
 
Basically a smart alternator - Any load on the alternator will transfer to resistance on the engine. so when full power is required the alternator will be backed right off to drop this load from the engine and again when the engine is slowing down or the driver is braking then power may be taken from the alternator to charge the battery / power the electrical items on the vehicle. The alternator in mine is 170 A or about 2.4kw thats a fair bit of power. The components coding required to do this is much less than the benefit it provides so its incorporated to add to the green credentials.
 
This;
http://www.z4-forum.com/forum/viewtopic.php?f=45&t=71492
could be touching on some off the problems with trying to be too clever by not having a traditional alternator/charging setup.
Knowing that failure off the roof could give the car a bad name, best look after the electrics by monitoring alternator and battery charging.
And pass it off as some fancy eco thing.
Load shedding by limiting the function of non essential services could be the first indication of charging or battery problems.
Maniac, haven't you said elsewhere about slow roof operation?
 
Nah I don't have a slow roof, it can be a tad jerky at times when the weight shifts as it moves tho which could be battery or a million other things.
 
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