[Lowrent]

Hi everyone,
I might have good news for those living in a snowy and icy country.

The recent Alex on Cars review turned my eyes wide open when he talked about regenerative braking. See Alex on Cars @ 24:17

It appears that what Tesla touts as "Regenerative braking" is in fact only "Lift off regeneration", when coasting.
As soon as you touch the brake pedal, you engage the real brakes. I was not aware of that.

I had a disappointing experience driving a Model 3 last winter, on a highway during a snow storm.
Every time I left my foot of the accelerator, I could feel the car moving left and right in a really scary manner.
The car was trying to regenerate, with the rear motor.
The solution was to turn off "Regeneration". All regenerative potential is lost but you gain control/safety in return.
Owners experiencing the same issue : Tesla forum - Youtube rear slip

In the Polestar 2, there is no way to turn off regeneration completely, the setting is for one-pedal driving only, aka "Lift off regen".
The car features blended braking; the brake pedal will always use true "regenerative braking" first, and engage the pistons only if you really need to brake, harder.

I was getting a bit concerned because if regeneration is not done right, I might experience the same problem as with the Model 3, and have no way to fix it.
I asked Polestar support some technical questions, not expecting much back, and got really insightful answers from Alane :

The maximum regenerative deceleration is 2.2 meters per second squared and happens typically around 70km/h.
Maximum regenerative peak power : 100kW
Brake bias : 60 (front) / 40 (rear).
Polestar 2 handles snow and ice quite well

Good, looks like a regular braking bias (brake more in the front than the back, to avoid rear slip).

I'm not an engineer but I assume it's feasible by having identical Permanent Magnet motors in the front and the rear.
They have the same "braking" potential and can be tuned accordingly .

The Model 3 has two different motors. A powerful one in the rear, doing all the job.
And an efficient one in the front, used rarely. Watch F Torque and R Torque in Bjorn testing AWD.
For comparison, the Model 3 maximum regenerative peak power is 60kW for RWD and 77kW for AWD.
Reason behind this choice is that the induction motor is really much better for the range, it can spin freely when not in use.

My guess/hope is that in exchange of shorter range on highway, we get better city-driving efficiency (stop and go) and better traction and regen on slippery roads.

 

[Doc S]

Great detective work, and good on polestar for giving out those details. Hopefully the real world experience follows the theory.
Another benefit of having a car designed in a northern country rather than California!

 

[polerad]

Hi everyone,
I might have good news for those living in a snowy and icy country.

The recent Alex on Cars review turned my eyes wide open when he talked about regenerative braking. See Alex on Cars @ 24:17

It appears that what Tesla touts as "Regenerative braking" is in fact only "Lift off regeneration", when coasting.
As soon as you touch the brake pedal, you engage the real brakes. I was not aware of that.

I had a disappointing experience driving a Model 3 last winter, on a highway during a snow storm.
Every time I left my foot of the accelerator, I could feel the car moving left and right in a really scary manner.
The car was trying to regenerate, with the rear motor.
The solution was to turn off "Regeneration". All regenerative potential is lost but you gain control/safety in return.
Owners experiencing the same issue : Tesla forum - Youtube rear slip

In the Polestar 2, there is no way to turn off regeneration completely, the setting is for one-pedal driving only, aka "Lift off regen".
The car features blended braking; the brake pedal will always use true "regenerative braking" first, and engage the pistons only if you really need to brake, harder.

I was getting a bit concerned because if regeneration is not done right, I might experience the same problem as with the Model 3, and have no way to fix it.
I asked Polestar support some technical questions, not expecting much back, and got really insightful answers from Alane :



Good, looks like a regular braking bias (brake more in the front than the back, to avoid rear slip).

I'm not an engineer but I assume it's feasible by having identical Permanent Magnet motors in the front and the rear.
They have the same "braking" potential and can be tuned accordingly .

The Model 3 has two different motors. A powerful one in the rear, doing all the job.
And an efficient one in the front, used rarely. Watch F Torque and R Torque in Bjorn testing AWD.
For comparison, the Model 3 maximum regenerative peak power is 60kW for RWD and 77kW for AWD.
Reason behind this choice is that the induction motor is really much better for the range, it can spin freely when not in use.

My guess/hope is that in exchange of shorter range on highway, we get better city-driving efficiency (stop and go) and better traction and regen on slippery roads.

If I understand you correctly, this system should also have better efficiency for accel/decel in general, so like highway stop and go and weaving through traffic.
I guess need to wait and see how this pans out in each of our own use cases, but does anyone know of an efficiency test with changing speeds over time, instead of the usual setting cruise control at a speed and keeping that for a while?

 

[polerad]

Hi everyone,
I might have good news for those living in a snowy and icy country.

The recent Alex on Cars review turned my eyes wide open when he talked about regenerative braking. See Alex on Cars @ 24:17

It appears that what Tesla touts as "Regenerative braking" is in fact only "Lift off regeneration", when coasting.
As soon as you touch the brake pedal, you engage the real brakes. I was not aware of that.

I had a disappointing experience driving a Model 3 last winter, on a highway during a snow storm.
Every time I left my foot of the accelerator, I could feel the car moving left and right in a really scary manner.
The car was trying to regenerate, with the rear motor.
The solution was to turn off "Regeneration". All regenerative potential is lost but you gain control/safety in return.
Owners experiencing the same issue : Tesla forum - Youtube rear slip

In the Polestar 2, there is no way to turn off regeneration completely, the setting is for one-pedal driving only, aka "Lift off regen".
The car features blended braking; the brake pedal will always use true "regenerative braking" first, and engage the pistons only if you really need to brake, harder.

I was getting a bit concerned because if regeneration is not done right, I might experience the same problem as with the Model 3, and have no way to fix it.
I asked Polestar support some technical questions, not expecting much back, and got really insightful answers from Alane :



Good, looks like a regular braking bias (brake more in the front than the back, to avoid rear slip).

I'm not an engineer but I assume it's feasible by having identical Permanent Magnet motors in the front and the rear.
They have the same "braking" potential and can be tuned accordingly .

The Model 3 has two different motors. A powerful one in the rear, doing all the job.
And an efficient one in the front, used rarely. Watch F Torque and R Torque in Bjorn testing AWD.
For comparison, the Model 3 maximum regenerative peak power is 60kW for RWD and 77kW for AWD.
Reason behind this choice is that the induction motor is really much better for the range, it can spin freely when not in use.

My guess/hope is that in exchange of shorter range on highway, we get better city-driving efficiency (stop and go) and better traction and regen on slippery roads.

Question-
If coasting is generally more efficient than regen, and if the brake pedal uses only regen for the first X% of travel, then wouldn't the most efficient driving style would be to turn 'one-pedal' off, coast as much as possible, and brake so that you only stay in the regen mode?

 

[rgledhill]

There are three modes for regen - off (coasts freely), low (minor regen on accelerator lift-off) and single-pedal mode. So you should be able to use "off" in the snow, I think?

And yes @polerad the most efficient way to drive is with zero regen, coast while you can, then use the brake pedal gently so it's all regen. One pedal driving tends to introduce lots of little accelerations and brakings, all of which waste energy in conversion.

 

[Doc S]

And yes @polerad the most efficient way to drive is with zero regen, coast while you can, then use the brake pedal gently so it's all regen.

Zero regen with light braking as most efficient certainly makes sense for highway driving. I'm not so sure it's as true for city driving with frequent full stops where you need to use friction braking too.
Looking forward to testing it out for myself....one day soon.

 

[JRRF]

What still needs to be accounted for in slippery conditions, is that regen doesn't use any ABS capability whereas friction brakes do. So at some point you want your friction breaks to kick in to keep you from skidding as you're stopping power increases. My current car also has blended brakes, and it's best in the snow to simply hit the brake pedal harder so that the ABS kicks in rather than just trying to use regen.

 

[Guy]

What is your current car? My ex 2015 Leaf was reducing regen as needed to keep the car from skidding.

 

[JRRF]

My daily driver is a Volt and I frequently drive a Bolt too. I've gotten them both to skid with pure regen. Maybe I was doing something wrong?

 

[TonyC]

Zero regen with light braking as most efficient certainly makes sense for highway driving. I'm not so sure it's as true for city driving with frequent full stops where you need to use friction braking too.
Looking forward to testing it out for myself....one day soon.

I'm not sure if this is widely known but the P2 regens with friction braking. Regen kicks in before the friction when brake pedal is depressed - one up on Teslas.

It's also wise to friction brake just for the hell of it as the performance of the brakes may degrade with lack of use - discs will rust over and pistons may seize.
Tony

 

[krheinwald]

Personally, I am not using OPD, as I think TPD (Two Pedal Driving) is more natural and is giving an extra degree of control. Nevertheless, I am sure this concerns OPD as well:

Is ABS active while braking on regen?

As I understand - and have experienced it over the last four weeks - the car will always brake using regen up to a certain deceleration (2.2m/S) which might lead to skidding in icy conditions. I couldn't find anything in the manual on this topic.

 

[JRRF]

I know other cars with blended braking have the same limitation with ABS. If you are regen braking the car will seem to fly forward if you hit ice or even a significant bump. The way around this is to simply hit the brakes as hard as you can in slippery conditions and let the ABS do it's magic.

Regardless, blended brakes are still way better for an EV.

 

[krheinwald]

I'm with you on the benefits of blended braking - when implemented properly. I do not hope blended braking is sending us back to pre-ABS times.

Not sure how hitting the brake hard to activate physical braking should help with preventing the strong regen from locking up your wheels, though.

All ABS does, is to briefly release the physical brake when it senses a wheel locking up. When regen is so strong - or the road is so slippery - that regen alone locks up the wheel, not braking - or releasing a brake - won't help.

Waiting for a reply from PS support, but not holding my breath for an answer.

 

[JRRF]

If you hit the brakes hard enough the friction brakes will take over and provide most of the deceleration and ABS function. In my current car I've tested this many times in the snow.

 

[krheinwald]

Is your current car a PS2? With regen being so strong on the PS2, ABS working on the mechanical brakes alone will probably not enough.

Is ABS active even when the mechanical brakes are not applied? I.e. does the ABS system sense lockes wheels due to regen breaking? In my feeling regen braking on the PS2 is so strong it could very well lock up the wheeks on its own. When ABS activates on the mechanical brakes, does it disable regen, as the locked wheels will most likeley not unlock with regen braking staying active.

I would assume/hope so. Looking for confirmation though, before being surprised by the opposite.

 

[ProfessorCook]

Can the regenerative action also be rapidly turned on and off? If so, your ABS system could work regardless.

 

[krheinwald]

As regen breaking is electronics only, it could - in theory - turn on and off even faster than you can modulate the brake pressure. Not sure about potential negative side effects on motors/electronics/batteries, though.

 

[JRRF]

Is your current car a PS2? With regen being so strong on the PS2, ABS working on the mechanical brakes alone will probably not enough.

Is ABS active even when the mechanical brakes are not applied? I.e. does the ABS system sense lockes wheels due to regen breaking? In my feeling regen braking on the PS2 is so strong it could very well lock up the wheeks on its own. When ABS activates on the mechanical brakes, does it disable regen, as the locked wheels will most likeley not unlock with regen braking staying active.

I would assume/hope so. Looking for confirmation though, before being surprised by the opposite.

I wish I was already driving my P2 😀. But in my current car I can regen over -50 kw with a blended brake system. All I can tell you is that ABS works very well with the brake pedal. What I can say is that the regen from one pedal driving does not engage the ABS. Whether the P2 system is substantially different I won't know until this winter. Hopefully I'll have the car by then 🙄.

 

[ProfessorCook]

I'll need to find a snow covered parking lot and do some research on this! ("No you see officer, I'm doing research here, sir." )

 

[krheinwald]

Please do. We won't see snow here until maybe January...