Opinion on regenerating brake

Yep same here, that's the DSC trying to help you get around those corners tighter. I really do not like how the intervention feels so I turn it off literally all the time unless the weather is bad. You should notice the car fights you less and is a much smoother cornering experience, but of course do so at your own risk as the nannies do prevent certain tendencies and can save your butt if your inexperienced (not directed at anyone in particular).

 

I think you may need to retest... straight from the manual:

Energy cannot be recovered in the following situations:

• Selector lever position N is engaged.
• While drive stability control systems, for instance DTC, are active and controlling the vehicle, even though this is not indicated by an indicator light.
• The high-voltage battery is fully charged.
• When temperature of the high-voltage battery is very low or very high.
• In winter it might be possible that the energy recovery is temporarily unavailable after startup.

I can both hear my brakes and feel the change in the brake pedal (more firm) at high SOC. It's also been documented that regen will cutout during aggressive cornering (bullet 2).

Are you using high regen? Because regen is not perfectly efficient, you'll never get back to above 100% SOC unless you start on a hill. The real limit is the current back into battery at high SOC (or during cold weather). The current from high regen is more than the battery can handle so brakes are blended in.

 

I will retest tomorrow after a full charge and try and see if I can capture it on video.

But also just because the battery cannot receive or recover the energy delivered from the motor, does not mean the motor itself cannot slow you down to a stop. The energy could be burned off through capacitors or resistors, but that I do not know.

What I do know, is that I should not be able to touch relatively cool brake discs after a stopping from 50+mph full regen if the brakes were facilitated.

 

It'll be a shared braking load between friction and regen so I don't think they'd get that hot after just one stop.

Try a slow speed with the windows down, it's pretty easy to hear them.

Or try pressing the brake pedal when slowing with regen. If it's firm without the typical squishy bit, the car is already using the brakes to slow down

 

Oh I can easily hear the brakes when they are being used, some of the most noisy brakes in a vehicle I've owned lol.

I will test with multiple runs and temp check after each run.

 

Kind of unrelated, but has anyone had problems with accidentally brake-checking people on the hard regen setting?

 

After getting used to the max regen setting (which took me about 5 minutes and my wife about 30 minutes because she never had a car with a manual transmission), such an accidental "brake-check" is as likely as accidently jamming one's foot on the brake pedal.

 

One quickly learns to be gentle with the right foot, unless one needs to slow quickly. (I'm thinking of those stop-and-go freeways.)

 

I stand corrected. My apologies to everyone for spewing false info before running a more conclusive test in the first place.

So as promised, I ran a much more extensive test and found that the SE does in fact blend friction brakes with Regen braking.

Fully charged, DSC fully off to eliminate any screwing of results, rotor temp check before leaving garage for baseline temps (avg 72.9°f).

Used my mainly empty rural neighborhood with many stop signs in a row to check temps at every stop, made it a point to hit 40mph everytime and immediate full max regen, no throttling. Once stopped, recorded temps, and immediately proceed to next run to keep rotors from cooling.

Finished testing with 98% soc.

Outdoor ambient 86°

Front and rear rotors Avg F. temps:
Baseline: 72.9°

1st stop: 76.3°
2nd stop: 79.1°
3rd stop: 84.2°
4th stop: 88.1°
5th stop: 92.7°
6th stop: 97.9°
7th stop: 101.3
8th stop: 101.8
9th stop: 102.5
10th stop: 102.9

Conclusive evidence of brakes being blended into Regen. I do want to note, that the amount of brakes being blended in is absolutely miniscule and is almost pointless IMO. The main slowing force is still the electric motor even at 100% soc. So friction brakes may equivalate to roughly 10-15% of declaration force, I suppose it's good for maintaining and keeping the surface rust at bay. What's also funny is I cannot hear or feel the brakes being blended in at all, but as soon as I breath on the pedal you can hear and feel them for sure. Engineers did a great job, at least on my MY23, on the blending.

Another worthwhile note is the plateau in temp increases the last 4 runs.

Another case in point, I let the brakes cool a bit, to around 90°, enabled roller mode, which turns off Regen braking 100% and made a 40mph stop with equivalent braking force as high Regen (Regen display bar/needle still works, possibly deceleration rate based...) and recorded a temperature of 138.6° after 1 stop. Huge difference from 1 run, im sure a 2nd run would have hit 150°...

My next quest is to find out what SOC% stops using blended brakes...

 

Nice data. Kudos to you for following up and in such a detailed manner.

 

Thanks for the data points - but you're not truly 100% charged when you're going from 40 to 0. You used some charge - less than 1 percent, but not nothing - to get to 40 mph, & you get some (but not all) of it back as you come to a stop. Is there an OBDII reader that shows 100ths of a percent SoC (mine only shows whole integers)? If so, that'd get you the %SoC returned to the battery if you looked right when you let your foot off the pedal & again when you come to a stop.

Otherwise if you always used only regen braking, then you'd always get home with the same SoC you left with, which is clearly not true.

 

I'm not quite sure what your getting at here. I was only providing data to prove, whether or not, that Regen braking blends in friction brakes.

Regen braking is clearly not able to recapture the energy spent accelerating, but that wasn't even the point of this test.

 

I don't think you'll find a consistent number here. My educated guess is the brake blending is ultimately controlled by the battery management system based on SOC, battery temp, and other factors to calculate a maximum acceptable current. It should somewhat follow the DC charging curve which tapers above 73%

I'm not sure how accurate it is but with a quick test at 65%, the instantaneous efficiency meter on the dash shows a maximum regen of -0.8mi/kWh. At the ~55mph I tested it at, that would be 68.7kW which is already higher than the DCFC peak. I guess this is possible because it's a short peak current vs the sustained charging?

I wonder if that -0.8mi/kWh is sustained at higher speeds or if brakes are blended in to reduce it. At 75mph, that would be 93.7kW!

 

This interesting thread showed up in my InsideEVs search as to how the Mini SE braking system works. I own a Kona EV but am considering the Mini EV in the future and am researching the relevant technologies. I was under the impression that the Mini has a simple electrically-boosted master cylinder like Tesla and perhaps the i3, but it looks like I'm mistaken.
The Kona has a fully-integrated unit combining a master cylinder, a second servo-motor-driven master cylinder and a number of solenoid valves that divert brake fluid as needed to prioritise regen over the disks whenever possible, within the motor's torque/power envelope. It includes ABS, stability and collision avoidance functions. In practice the disks appear to be only applied when under a walking pace (or of course when the car is coasting in Neutral or the battery is at 100%) and there is no perceptible transition other than the slight sound of the pads touching the disks.
Does the Mini work like this or does it rely on accelerator-based regen only?

 

Accelerator regen only, the brake system does not add any regen. I believe it uses an electric vacuum pump (from the i3) and shares the same brake components as the ICE MINI

 

The dynamic slip control (DSC) unit (passenger glovebox area) probably has expanded duties to regulate front/rear brakes and throttle input during brake regen. It's the same part #34517916190 as the X1/X2/i3. You could probably go as far back as 2007 on BMWs to see what they were doing for 12V battery regen as well.

Honestly I prefer one-pedal driving using high brake regen on the MINI. High regen feels like 1st gear engine braking, and low regen feels like 4th gear engine braking (at higher speeds).

 

Somehow this post slipped under my 'inside evs' radar - I missed it. Very interesting. Thanks for testing this out!

 

I'm pretty sure the regen traction control is done by the inverter (aka ECU below), it's the same control as preventing wheel spin just in reverse. Also, DSC is dynamic stability control

Here's a slightly credible source

"which has a special traction control system called ‘Active Slip Regulation’... Mini says it’s quicker reacting because the system is actually integrated into the ECU, basically just a few lines of code, so doesn’t have its own dedicated control unit."​

 

I can tell you from driving a pre-LCI i3 that the traction control in the SE is 50X better, and the i3 was no slouch either. The traction system is one of the most impressive parts of this car.

 

Thanks my smooth brain isn't so great for late night!

So this Active Slip Regulation works for acceleration, would it also be used for regenerative braking to blend in the friction brakes?