Why regenerative braking belongs on the brake pedal

[mongo]

I grew up on manual cars, so I am used to the accelerator also being a decelerator.
Usability question for brake pedal induced regen: Say I'm on an open freeway through the mountains and I want to reduce speed on the downhills, but do not want to use any physical brakes (I don't mind being over the speed limit in this situation), how would I do that?


Edit for clarity: I like the Tesla way, this question was meant to show a potential issue with going to a regen on brake pedal system. Personally, I'd like a flappy paddle style lever on the steering wheel to engage regen (variable levels) or disable it (bad road conditions)

 

[EdA]

I grew up on manual cars, so I am used to the accelerator also being a decelerator.
Usability question for brake pedal induced regen: Say I'm on an open freeway through the mountains and I want to reduce speed on the downhills, but do not want to use any physical brakes (I don't mind being over the speed limit in this situation), how would I do that?

Just ease up on the accelerator, you shouldn't need any physical brakes.

 

[nvx1977]

I grew up on manual cars, so I am used to the accelerator also being a decelerator.
Usability question for brake pedal induced regen: Say I'm on an open freeway through the mountains and I want to reduce speed on the downhills, but do not want to use any physical brakes (I don't mind being over the speed limit in this situation), how would I do that?

In traditional implementations of regen on brake pedal, you can't tell at which point you're relying purely on regen and when friction braking is assisting. In a previous post, I suggested one usability improvement would be to place a tactile feedback mechanism in the brake pedal so you can feel when you've hit the threshold. Kinda like camera shutter buttons with 2 click levels - one for autofocus, and another to take picture.

I think a lot of us who drove manual will easily accept regen on accelerator (like downshifting to utilize engine braking) and no creep because manuals couldn't creep either.

 

[daniel]

I grew up on manual cars, so I am used to the accelerator also being a decelerator.
Usability question for brake pedal induced regen: Say I'm on an open freeway through the mountains and I want to reduce speed on the downhills, but do not want to use any physical brakes (I don't mind being over the speed limit in this situation), how would I do that?

You can't. Regardless of where the regen is located, there's a limit to how much regen you can get. I presume that the Prius (with regen on the brake pedal) is using all regen until it's at maximum regen, and then engages the friction brakes. You slow down as much as you need to to maintain your speed, and presumably the car is using regen for as much of that as it can.

In a Tesla, with your foot off the go-pedal you'll get as much regen as the car can produce under the conditions, and you'll use the brake pedal if the regen isn't enough to maintain your speed.

 

[Krazaak]

I skipped all but the first and last pages, but I'm happy with the Tesla regen setup. I actually wouldn't mind them adding a variable regen defeat pedal to the left of the brake. It wouldn't be used often, but it might be useful in low traction conditions where I want to limit the regen strength but have my foot over the brake. I could see it being particularly useful on RWD models, where you might want to apply light front and rear braking, but not have full regen engaged on the rear wheels.

 

[Rocky_H]

I skipped all but the first and last pages, but I'm happy with the Tesla regen setup. I actually wouldn't mind them adding a variable regen defeat pedal to the left of the brake. It wouldn't be used often, but it might be useful in low traction conditions where I want to limit the regen strength but have my foot over the brake. I could see it being particularly useful on RWD models, where you might want to apply light front and rear braking, but not have full regen engaged on the rear wheels.

All of this that you mention is accurate and useful, but the method instead of an additional pedal is to just change the regen setting to Low. That eases it up so it won't break loose the traction of the rear wheels in icy conditions.

 

[Krazaak]

All of this that you mention is accurate and useful, but the method instead of an additional pedal is to just change the regen setting to Low. That eases it up so it won't break loose the traction of the rear wheels in icy conditions.

Yeah, that does the trick as long as you've prepared properly, but it gets a bit cumbersome on a trip where you want to benefit from regen where you can and switch to lower regen only when you need it.

 

[Rocky_H]

Yeah, that does the trick as long as you've prepared properly, but it gets a bit cumbersome on a trip where you want to benefit from regen where you can and switch to lower regen only when you need it.

Why would you think so?
(1) Prepared properly -- It takes a few seconds to make this change either way while you are driving. You don't need to put this on your packing list and change the setting days ahead of time. So if it's snowing while you're driving, change it. You should have it ready before the instant you need it anyway. Better than trying to instinctively remember to use an additional pedal you don't normally use.

(2) "on a trip" -- When you are on those longer highway drives, you're in cruise control with your seed steady most of the time, and not doing a lot of intense speeding up and slowing down for the most part, so there's not a lot of gain to be had with higher regen overall anyway. So it's not all that relevant on long trips. It's mostly needed in city driving when you are doing more speed up and slow down, and yes, you should have it on Low regen on those days when it's icy.

 

[arnis]

Tesla's "brake pedal as only friction brake" is ok and Leaf's more complicated approach too.
Though Tesla does actually lack adjustment. Max and Low is not enough for everybody.
Off should also be available and Medium also.
On the other hand, brake blending should be a thing. And Tesla doesn't do that.
That means if regen is set to low or off, pushing brake pedal always starts with regen. Tactile feedback is welcome.
In case of FWD or RWD vehicle, blending starts with non-driving wheels' friction brakes. Until friction brakes apply
about the same braking action as regen. In case of slippery conditions, compensation should happen (regen limited
to whatever value and non-driving wheels continue with friction brakes).

Brake blending is not easy, I agree. But some manufacturers have shown perfect 10/10 results. So it can be done.

Another approach without brake blending would be brake handles behind the steering wheel.
But not click-click type, but rather pressure sensitive (piezo type) with max-tactile-click in the end.
Coast with no pedals and adjust regen smoothly with handle(s). If that is not enough, use friction brakes.
This way, brake blending can be "bypassed".
Bolt has something similar, but it is OnOff button. Not good enough for comfort.

Separating regen from accelerator allows wider range adjustment for accelerator travel. That means more comfort and
more precise adjustments.
Right now, it looks like that (just an approximation):
0% -70kW
10% -30kW
20% -10kW
30% -0kW (coast)
40% 10kW
50% 30kW
60% 60kW
70% 130kW
80% 200kW
90% 300kW
100% 400kW
Notice how hard it is to drive efficiently without cruise control. Pedal should stay between 30%-60% all the time.
If we remove negative torque (0%-30%) we can expand accelerator travel.
And also, we can expand regen (secret: EV motor can actually regen as much as it can accelerate, battery can accept charge no slower than it can be charged, so no less than 100kW for Tesla). Win-win situation. 100kW regen is too much for comfort (and it is often not available). This is why Tesla (and all other manufacturers) have their own fixed "max" value when accelerator is released (secret2: Leaf has 30kW limit, but actually, with additional brake pedal, it will regen up to 50kW and then blend with friction, it will never show that on the graph though).

 

[mongo]

Tesla's "brake pedal as only friction brake" is ok and Leaf's more complicated approach too.
Though Tesla does actually lack adjustment. Max and Low is not enough for everybody.
Off should also be available and Medium also.
On the other hand, brake blending should be a thing. And Tesla doesn't do that.
That means if regen is set to low or off, pushing brake pedal always starts with regen. Tactile feedback is welcome.
In case of FWD or RWD vehicle, blending starts with non-driving wheels' friction brakes. Until friction brakes apply
about the same braking action as regen. In case of slippery conditions, compensation should happen (regen limited
to whatever value and non-driving wheels continue with friction brakes).

Brake blending is not easy, I agree. But some manufacturers have shown perfect 10/10 results. So it can be done.

Another approach without brake blending would be brake handles behind the steering wheel.
But not click-click type, but rather pressure sensitive (piezo type) with max-tactile-click in the end.
Coast with no pedals and adjust regen smoothly with handle(s). If that is not enough, use friction brakes.
This way, brake blending can be "bypassed".
Bolt has something similar, but it is OnOff button. Not good enough for comfort.

Separating regen from accelerator allows wider range adjustment for accelerator travel. That means more comfort and
more precise adjustments.
Right now, it looks like that (just an approximation):
0% -70kW
10% -30kW
20% -10kW
30% -0kW (coast)
40% 10kW
50% 30kW
60% 60kW
70% 130kW
80% 200kW
90% 300kW
100% 400kW
Notice how hard it is to drive efficiently without cruise control. Pedal should stay between 30%-60% all the time.
If we remove negative torque (0%-30%) we can expand accelerator travel.
And also, we can expand regen (secret: EV motor can actually regen as much as it can accelerate, battery can accept charge no slower than it can be charged, so no less than 100kW for Tesla). Win-win situation. 100kW regen is too much for comfort (and it is often not available). This is why Tesla (and all other manufacturers) have their own fixed "max" value when accelerator is released (secret2: Leaf has 30kW limit, but actually, with additional brake pedal, it will regen up to 50kW and then blend with friction, it will never show that on the graph though).

I may be off, but I think the pedal position maps to speed such that the constant velocity position is further down the pedal the faster you go. Deviations from the matched speed cause additional power allocation. Otherwise,like you mentioned, the usable band would be super small. (full regen to full acceleration pedal mapping without the speed factored in would make power matching low single digit velocities difficult/impossible).

People with Teslas: At a standstill, does the top of the range still map to regen (such that there is a dead band), or does it provide low torque drive?

 

[arnis]

I may be off, but I think the pedal position maps to speed such that the constant velocity position is further down the pedal the faster you go.

It should. My BMW had ABS sensor failure lately (one that was also responsible for speed signal) and driving it was a nightmare. Keeping pedal steady kept the power output also steady, even though speed got up, power was fixed. Trying to get to constant speed with adjustment was literally impossible. To drive at 100km/h one needs to hold the pedal at 31.5% +/- 0.1%, not possible to even find that spot. And oh god when road goes 0.5% uphill
As I fixed the sensor thing, it went back to normal. AFAIK, it even compensates slightly for speed change due to hills. So keeping pedal steady, speed at 100km/h, if speeds starts to drop, motor torque raises.
Like I said, simplification for sure. But overall idea is the same. I've done that with Leaf (reduce regen and note the simplification of adjustment). Same can be done with Tesla (regen low and observe).

I would definitely want to have regen adjustability with my fingers.
In case of Dual motor, one could adjust regen of front and rear axle independently with left-right flap. How awesome would that be

 

[Helmuth]

I didn’t read all the posts!

But I love the (more or less) one pedal driving with the Model X!
Why should I want to move my foot to the break pedal all he time if it’s enough to (partly) let go the accelerator?
It’s much more relaxing fo me to get used to the one pedal driving and using the brake pedal just to come to a complete stop...

 

[insaneoctane]

As several Model S owners have reported, once you're used to one-pedal driving, losing regen completely due to a cold or hot battery can be a real shock. (NPI) If regen is on the brake, this wouldn't be noticeable.

While I will not likely ever experience this problem in my geography, I appreciate it. Tesla could easily fix this OTA by using friction brakes to simulate regen until things warm up. They could throw an icon or info line on the screen to tell you how much this is happening. It would be more consistent, predictable and safer...

 

[SDRick]

I love the (more or less) one pedal driving with the Model X!
Why should I want to move my foot to the break pedal all he time if it’s enough to (partly) let go the accelerator?
It’s much more relaxing fo me to get used to the one pedal driving and using the brake pedal just to come to a complete stop...

Bingo!!!

 

[daniel]

People with Teslas: At a standstill, does the top of the range still map to regen (such that there is a dead band), or does it provide low torque drive?

I don't understand the question. Top of the range of what? What does "map to regen" mean? Dead band?

If you do not touch either pedal (top of the range of motion of the pedals) the car creeps forward (like an automatic) if you have selected Creep On. The car does not move if you have Creep Off.

 

[mongo]

While I will not likely ever experience this problem in my geography, I appreciate it. Tesla could easily fix this OTA by using friction brakes to simulate regen until things warm up. They could throw an icon or info line on the screen to tell you how much this is happening. It would be more consistent, predictable and safer...

I get where you are coming from, but I'd rather have the car do nothing on accelerator let up than brake. That is a totally unrequested action (And would be hard to implement based on brake performance, road condition, deceleration mapping)

 

[mongo]

I don't understand the question. Top of the range of what? What does "map to regen" mean? Dead band?

If you do not touch either pedal (top of the range of motion of the pedals) the car creeps forward (like an automatic) if you have selected Creep On. The car does not move if you have Creep Off.

My bad, top of the accelerator meaning the first bit of pressing.

Basically, does the same accelerator position do different things based on the speed the car is going.
If car is stopped 5% throttle is a slow acceleration. 15% is faster acceleration.
At 65 MPH does 15% keep you at a constant speed and 5% is moderate regen.
Versus
5% is always regen and 15% is always acceleration.

 

[Uncle Paul]

Tesla's regen on pedal is well thought out, even if some circumstances would make putting it on the brake pedal might be better.

For the casual driver it makes all the sense in the world. Need torque, press the pedal. More pedal = more torque. If you want no torque lift on the pedal until torque is gone. If you want negative torque, release the throttle more, until you get the precise negative throttle you desire.
If full release does not produce enough negative torque, add brake pedal as desired.

Set up for super easy one pedal driving most of the time, with significant regeneration produced when calling upon negative torque.
Regen can produce better than 90% of the braking force desired for daily driving by an aware driver, with mechanical braking being reserved for the final 10% to bring the vehicle to a full stop.

The reason not to use regen to fully stop the vehicle is that it is a good idea to use the mechanical brakes from time to time to keep them in good working order.

For most owners, driving a Tesla is an enjoyable and rewarding experience. Those desiring a system to be optimized for racing, snow covered roads, etc. might be able to make a case for a different system, but for most of us, the Tesla system works just fine.

 

[MXWing]

Please educate yourself first before commenting.

You are aware that there are two ways to decelerate a vehicle that isn't going downhill right?

1.) Letting your foot off the accelerator
2.) Using the brakes to apply friction in addition to #1?

If you can slow a car down, would you rather do it in 1 step or 2 steps?

I think I will go vape some tide pods before revisiting this thread. This "thesis" may make more sense to me then.

 

[daniel]

My bad, top of the accelerator meaning the first bit of pressing.

Basically, does the same accelerator position do different things based on the speed the car is going.
If car is stopped 5% throttle is a slow acceleration. 15% is faster acceleration.
At 65 MPH does 15% keep you at a constant speed and 5% is moderate regen.
Versus
5% is always regen and 15% is always acceleration.

Okay. Now I understand the question. Unfortunately, I don't know the answer.

I am kind of under the impression (but only vaguely) that accelerator position is mapped to speed. If you have the accelerator at a faster speed than the car is going, it will accelerate. The greater the distance between pedal position and car speed, the greater the acceleration. If the pedal position is less than the car's speed, it will apply regen, again proportional to the spread between pedal position and actual speed. Except that the slower the car is going, the less regen you can get. Below a certain speed there might not be any regen. But also, of Creep is set to On, then below a certain speed it will move when the pedal is at zero.

I could be completely wrong about all the above, but that's my very ignorant understanding.