Model X Brake Pedal - Friction or Regen?

[Falcon73]

Now that Scan My Tesla is working, I made an interesting discovery today. The brake pedal wasn't activating any regen. On non-Tesla BEVs I've driven, including our current stablemate the Volvo C40, the brake pedal will do regen first and then add the friction brake as needed. So, even with 1-Pedal "off" on the C40 it will still regen when braking with the brake pedal.

I don't remember what my 2021 MYLR did as the regen was always so strong on it anyway and I didn't think to test pushing the brake pedal while watching the power meter on Scan My Tesla.

I wonder if this is a Tesla thing or something else. Why wouldn't pressing the brake activate regen automatically?

So, I'm testing Low vs Standard regen on our 75D MX. So far, the range is looking to be less than expected, but still a lot more than the Leaf with the fried battery.

 

[KiwiME]

I own a Kona Electric which has blended braking and have been researching what other EVs have and don't have that feature, in case I decide to move on from the Kona. The Kona was intended to be driven like any other car and transparently uses regen optimally whenever possible, right down to a a walking pace. The system was initially used in the classic Ioniq and now the third generation hardware is used in the current Ioniq 5 / EV6 models. The unit also incorporates ABS and collision avoidance (autonomous) braking.

My understanding is that Tesla has not developed such a system and I would imagine it's not cheap to do so. I guess it's a matter of philosophy - should an EV require a different driving technique for maximum efficiency, e.g. one-pedal?

As an interesting side point the "master cylinder" unit costs more than the gearbox so I'm not going to skip on brake fluid changes.

 

[DCGOO]

I own a Kona Electric which has blended braking and have been researching what other EVs have and don't have that feature, in case I decide to move on from the Kona. The Kona was intended to be driven like any other car and transparently uses regen optimally whenever possible, right down to a a walking pace. The system was initially used in the classic Ioniq and now the third generation hardware is used in the current Ioniq 5 / EV6 models. The unit also incorporates ABS and collision avoidance (autonomous) braking.

My understanding is that Tesla has not developed such a system and I would imagine it's not cheap to do so. I guess it's a matter of philosophy - should an EV require a different driving technique for maximum efficiency, e.g. one-pedal?

As an interesting side point the "master cylinder" unit costs more than the gearbox so I'm not going to skip on brake fluid changes.

Tesla does “blended” braking. But the regen braking from just reducing the accelerator is so effective, touching the brake pedal is almost never required. There are a few instances when regen is not as effective, like when it is very cold (less than -10°C) or the battery is at 100%. Normally you will see a warning under those conditions. But if you are stepping on the brake, regenerative is also fully engaged.

Tesla does not call for any brake fluid changes, unless deemed necessary. Check it every two years is recommended. It is very rare that change is indicated. BTW, this should be done at the Service Center. There are specific procedures called for to avoid contaminating the system. Tesla has intentionally made it difficult to access for that reason.

 

[brainhouston]

Tesla has intentionally made it difficult to access for that reason.

Agree with everything else but its not difficult. Reservoir cap is right under the windshield on the drivers side just like any other car...

 

[MP3Mike]

I wonder if this is a Tesla thing or something else. Why wouldn't pressing the brake activate regen automatically?

On current Teslas the regen is fully activated when you fully let off of the accelerator. There is no additional regen available, so there is nothing for the brake pedal to activate.

 

[DCGOO]

Agree with everything else but its not difficult. Reservoir cap is right under the windshield on the drivers side just like any other car...

Yes but you have remove the large plastic cover first. They definitely do not want the owner to be opening that system. The only exposed fill port is for windshield washer fluid.

 

[brainhouston]

Yes but you have remove the large plastic cover first. They definitely do not want the owner to be opening that system. The only exposed fill port is for windshield washer fluid.

True but u also have to remove that plastic to jump start/replace battery/fuses etc. I don't consider that "intrusion prevention"

 

[brainhouston]

On current Teslas the regen is fully activated when you fully let off of the accelerator. There is no additional regen available, so there is nothing for the brake pedal to activate.

I guess one possibility is if Low regen is ON for older cars... then brake should activate full regen... would be curious if its like that or not

 

[DCGOO]

True but u also have to remove that plastic to jump start/replace battery/fuses etc. I don't consider that "intrusion prevention"

None of those things are considered owner service either. It doesn't mean you can't. It just means not recommended that you try. If access is exposed and labeled, it means they expect the owner to access it routinely. If it is hidden away and covered up, factory tech support is suggested. Heck, I've drilled through the roof of my X to mount antennas and torn in to the electrical system for low voltage power. But I've stayed away from things like the brake fluid that I am very likely to damage.

 

[Falcon73]

I guess one possibility is if Low regen is ON for older cars... then brake should activate full regen... would be curious if its like that or not

From my driving and testing since my OP, at least according to Scan My Tesla, braking isn't increasing my "Low" Regen, so it doesn't seem to blend. It seems that any time I'm pushing the brake pedal it only adds the friction brakes.

I suppose a better way to tell would be the max regen I see. It typically maxes out on the -30kW range, but it can go to 50. I'm thinking max regen should be more on our '17 MX.

Let me test more on Standard regen. I don't like that mode as I still have to use the brakes at low speed and one needs to be ready for it when regen lets go, unlike our former '21 MYLR which definitely DID do One Pedal to a stop.

 

[brainhouston]

None of those things are considered owner service either. It doesn't mean you can't. It just means not recommended that you try. If access is exposed and labeled, it means they expect the owner to access it routinely. If it is hidden away and covered up, factory tech support is suggested. Heck, I've drilled through the roof of my X to mount antennas and torn in to the electrical system for low voltage power. But I've stayed away from things like the brake fluid that I am very likely to damage.

Everyone entitled to their opinion but i think it was meant to be accessible by owners just not as often as washer fluid. Very clever actually.
Depending on your expertise n comfort u can service more things that were meant or not.

FYI, Jump starting is on Tesla DIY page, so yeah it was intended to be accessible by user occasionally.
There's a reason its removable by hands without any tools.

 

[KiwiME]

Tesla does “blended” braking. ... But if you are stepping on the brake, regenerative is also fully engaged.

On current Teslas the regen is fully activated when you fully let off of the accelerator. There is no additional regen available, so there is nothing for the brake pedal to activate.

I guess one possibility is if Low regen is ON for older cars... then brake should activate full regen... would be curious if its like that or not

From my driving and testing since my OP, at least according to Scan My Tesla, braking isn't increasing my "Low" Regen, so it doesn't seem to blend. It seems that any time I'm pushing the brake pedal it only adds the friction brakes

Thanks everyone for responding and sorry for not getting back earlier. We don't seem to have an agreement on the question of "does pressing the brake pedal add more regen than is already present".

From a basic motor control perspective, regen is nothing more than the (upper-left) quadrant where the direction is forward and the torque is opposing that. So, does pressing the brake pedal add to any regen already present before engaging friction brakes? Specifically I'm referring to the Model 3/Y cars, if that matters. My understanding from other owners I've asked is that it doesn't, and I'm trying to confirm this one way or the other.

I'm also asking the same question of Mini E owners and to be fair they don't seem to agree either. The easiest way to check this is to watch the power indication with your foot off the accelerator, before and after touching the brake pedal. You should be able to hit very high regen power levels under hard braking, within the motor(s) torque envelope of course.

 

[KiwiME]

I see it's been addressed in this thread.

Does the brake pedal activate regenerative braking before the brake pads apply friction?

I'm not a fan of one-pedal driving, but I'm a fan of regenerative braking for longer range. So, I would hope that it's possible to set the car to coast in a manner similar to gas-powered car, but also that when the brake pedal is depressed, it uses regen braking before the brake pads. Friction...

teslamotorsclub.com

 

[EbS-P]

I guess one possibility is if Low regen is ON for older cars... then brake should activate full regen... would be curious if its like that or not

That probably means break by wire. Does anyone do that?

 

[brainhouston]

That probably means break by wire. Does anyone do that?

Not necessarily, it could just be tied to brake switch...
I think Prius is using some sort of blended braking...

 

[EbS-P]

Not necessarily, it could just be tied to brake switch...
I think Prius is using some sort of blended braking...

They have a planetary gear set and clutches.

 

[KiwiME]

It's certainly not just a wire off the brake light switch. Although electric brakes just happen to be under development now by Brembo, automakers currently stick with proven, low-liability-risk hydraulic technology. ABS/ stability control and collision avoidance systems are also considerations and can be combined rather than having separate units. Hyundai/Kia have developed a fully-integrated unit that does everything, video below, excuse the annoying music. There is an electrically-driven second master cylinder that does three functions , (a) provide force feedback to the foot pedal when in regen mode, (b) modulate the disk brakes in ABS mode, and (c) activate the brakes in collision avoidance mode.

The advantage of having a blended brake system is that (a) the driver has the option to drive the EV exactly like a conventional car without giving up anything in overall efficiency, (b) off-accelerator fixed regen levels can be lower (or zero) to exploit kinetic energy for coasting without having to position your right foot precisely at a transition point, and (c) brakes can be smoothly engaged at low speeds when no power can no longer be extracted from the motor.

It's worth noting that regen incurs losses of around roughly 25-30% and so the "rubber band" mode of driving is not ideal, if optimal efficiency is a consideration. Nissan seem to have something similar and even GM's 1990s EV1 had the origins of such a system.

 

[brainhouston]

i was simply stating that having car computer activate regen when it sees brake switch input (tapped/pressed brake pedal) is easy n much better option in my opinion rather than full on blasting regen when u let off accelerator...