THE BMW ActiveE FORUM

[woof]

Originally Posted by TomMoloughney

Unfortunately, I don't kow how this can be engineered out of the cars (and evidently neither does the engineers at BMW, Tesla, Toyota and the other OEM's that are making cars with regen) because there are conditions when the regen needs to deactivate.

In the case of our ActiveE's, when the traction control detects slippage, or loss of contact between the wheels and road surface, the car will suddenly disengage the regen. It needs to do so because you run the risk of total loss of control if the rear wheels begin to slip and the regen continues to apply resistance to slow the car down. This could be disasterous on icy road conditions or if you are un a turn, or going down a hill, etc. The traction control HAS to overide the regen because if the regen is allowed to continue to try to slow the car down while the tires are slipping you'll lose all traction. Do you apply the friction brakes when a car is slipping or skidding? Of course not, you'll have no control at all.

As I wrote in a previous thread about this, regen is only applied to two of the four wheels, unlike friction braking which is applied to all four wheels. Thus, when traction control cuts regen, it removes ALL braking force, not just from the wheels that are slipping as would occur during TC with all four friction brakes being applied.

I think the effect of disabling regen on the rear wheels during traction control events could be mitigated by applying friction braking to the front wheels during that time.

It'll be interesting to see how the Tesla Model X handles this, as it will have all wheel drive, and thus regen on all wheels.

[Reddot]

This happens to us daily.

[nilsbunger]

I agree I think it's just caused by regen disconnecting when it detects slippage. But it does feel scary, likethe car is surging forward, because you mentally treat regen as part of the braking.

The regen is only from the back wheels, which is probably why it kicks out more easily than abs brakes do.


Maybe the answer is for BMW to auotomatically apply the brakes a little bit when regen kicks out?

[Dominik]

I have that happen a lot too. downhill wile using regen / slight brake form high spee. I feel the surge and the Cahring/Drive gauge jumps from MAX regen to half regen - or so.

Tom's post outlines it very well and it matches my thoughts. I also thought that it can happen if the battery gets charged to fast.

But if you're prepared for it it's no big deal.

[TomMoloughney]

Originally Posted by Dominik

I have that happen a lot too. downhill wile using regen / slight brake form high spee. I feel the surge and the Cahring/Drive gauge jumps from MAX regen to half regen - or so.

Tom's post outlines it very well and it matches my thoughts. I also thought that it can happen if the battery gets charged to fast.

But if you're prepared for it it's no big deal.

But if you're prepared for it it's no big deal

Exactly. After driving these cars for three years now, It's second nature and I don't even flinch. It's never created a dangerous situation or any issue as soon as I figured out what was going on. I have to admit when I first encountered this it was quite unsettling and I thought there was a problem with the car.

[wchung1]

Originally Posted by TomMoloughney

But if you're prepared for it it's no big deal

Exactly. After driving these cars for three years now, It's second nature and I don't even flinch. It's never created a dangerous situation or any issue as soon as I figured out what was going on. I have to admit when I first encountered this it was quite unsettling and I thought there was a problem with the car.

With this is mind, I am trying to be more cautious when I am coming down a hill. Maybe a dumb question here. What do you when this does occur pr about to? Thanks for your help and others. I am curious is Matt from BMW has anything to add.

[TomMoloughney]

Originally Posted by wchung1

With this is mind, I am trying to be more cautious when I am coming down a hill. Maybe a dumb question here. What do you when this does occur pr about to? Thanks for your help and others. I am curious is Matt from BMW has anything to add.

With all respect to BMW_Matt and even the BMW engineers that can give you a technical explanation of why it happens or how it may be possible to improve(minimize) on the effect in future models, this is one example of an issue that your much better served talking to someone like me or someone else that has driven EV's for a while - in my case over 80,000 miles.

This is how I deal with it:

When I'm using regen, I always try to assume it can cut out at any time so I'm ready with my left foot to apply the friction brakes in circumstances that could create a problem if the regen does get interrupted. For example going around a tight turn or slowing down with a car in front of me. However, if I'm using regen going down a hill and there are no other cars on the road and losing regen wouldn't cause any issue then I probably wouldn't be at the ready though. For me, I found that the only time it could cause an issue is if I was either going too fast, or was driving too close the the vehicle in front of me.

The biggest thing is just being mentally prepared that the regen could cut out if traction control detect a problem. Even with out consciously thinking about it, my brain has been trained to be ready to quickly snap at the friction brakes.

It also important to leave enough space between you an the cars in front of you. I know you already know this, but I've learned to allow a bit more space between me and the car I'm trailing to let me use the regen and glide mode more efficiently. By leaving a bigger gap between vehicles(When possible) and gradually accelerating and decelerating you will dramatically improve your consumption rate, and there's an added bonus, your driving more safely!

I know this may sound like a lot, but if you practice for a while you'll see it not difficult to adjust your driving and then you'll do it naturally. Then even when you drive a gas car you'll be more efficient and safer.

[Dominik]

Originally Posted by TomMoloughney

talking to someone like me or someone else that has driven EV's for a while - in my case over 80,000 miles. ...


I know this may sound like a lot, but if you practice for a while you'll see it not difficult to adjust your driving and then you'll do it naturally. Then even when you drive a gas car you'll be more efficient and safer.

This is excellent advice! We are not (yet) in the age of self-driving cars, so driver skill is important.
Airplanes and cruise ships all will still require a skilled pilot. I think it is impossible to have a perfect response form the control systems at any time (I am a software engineer).


Thus the advice Tom gave is great. The driving will be smoother and the stress on the car will be less. This will go toward longevity of the suspension and drivetrain. As a race car driver one told me - smooth is fast and safe.

[electricb]

Originally Posted by TomMoloughney

With all respect to BMW_Matt and even the BMW engineers that can give you a technical explanation of why it happens or how it may be possible to improve(minimize) on the effect in future models, this is one example of an issue that your much better served talking to someone like me or someone else that has driven EV's for a while - in my case over 80,000 miles.

This is how I deal with it:

When I'm using regen, I always try to assume it can cut out at any time so I'm ready with my left foot to apply the friction brakes in circumstances that could create a problem if the regen does get interrupted. For example going around a tight turn or slowing down with a car in front of me. However, if I'm using regen going down a hill and there are no other cars on the road and losing regen wouldn't cause any issue then I probably wouldn't be at the ready though. For me, I found that the only time it could cause an issue is if I was either going too fast, or was driving too close the the vehicle in front of me.

The biggest thing is just being mentally prepared that the regen could cut out if traction control detect a problem. Even with out consciously thinking about it, my brain has been trained to be ready to quickly snap at the friction brakes.

It also important to leave enough space between you an the cars in front of you. I know you already know this, but I've learned to allow a bit more space between me and the car I'm trailing to let me use the regen and glide mode more efficiently. By leaving a bigger gap between vehicles(When possible) and gradually accelerating and decelerating you will dramatically improve your consumption rate, and there's an added bonus, your driving more safely!

I know this may sound like a lot, but if you practice for a while you'll see it not difficult to adjust your driving and then you'll do it naturally. Then even when you drive a gas car you'll be more efficient and safer.

This is good advice. I have experienced over the last few months and usually it happens over broken pavement with a slight bump. I have just prepared myself that I will feel that weird "surge" when I go over certain bumps.

[djm12]

Originally Posted by Reddot

This happens to us daily.

My wife and I have not noticed any loss of braking in 2000 miles of driving. So either we have just incredibly lucky or all Active Es are not alike. Maybe BMW is testing various software settings on different cars.