Why regenerative braking belongs on the brake pedal

[MXWing]

Please educate yourself first before commenting.

Flames to /dev/null

You gonna tell me next why I'm ignorant for building out IP4 infrastructure when I should be using the vastly superior IP6?

To do yourself a favor, I would not have a link to this article on your Github.

I will easily dismantle your rant below.

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"Regen helps improve overall efficiency, but relatively marginally."

Marginally depending on slope right?

"During oversteer, the tires at the rear of the car lose traction before the fronts. This can happen under extreme limit conditions such as an emergency while driving on the street or much more commonly during the rigors of racing. NASCAR <SNIP>"

I got all excited until I saw NASCAR and then I got sad as I would never run into this scenario with my remaining time on this flat earth.

"significant ergonomic and safety error that may contribute to crashes."

Can you cite a SINGLE source where regen on the throttle has been attributed to a crash?

"All major, modern race cars such as Formula One are mid-engined where the engine is in front of the rear axle, which is optimal weight distribution."

I am FURIOUS at Elon right now. First he said the Model 3 was a spaceship (he lies) and he didn't even know to incorporate Formula One mid-engine design into Teslas? Shame on him.

"But again most of the above only really comes into play during racing."

Right, I RACE to the mall. I RACE to Taco Bell. I RACE to soccer practice.

"Tesla drivers may disagree with the above, but most of their experience will be informed by a very limited set of driving experiences typical of most street use, and not racing, limit behaviors or emergency maneuvers."

Why did you leave out Jaguar, Honda, Toyota, Fiat, Ford, Chevrolet, Rimac.. etc etc etc? Or

Is it only Tesla drivers that drive on the street? Everyone else RACES from stoplight to stoplight
going up to 120MPH and rely on regen to slow them down?

"I happened to have a long talk with a Tesla engineer and brought up this issue with him. He mentioned that there were two camps of thought about it inside Tesla. Some agree that heavy regen belongs on the brake pedal and others feel it belongs on the throttle."

There was a layoff at Tesla last year. Hope they closed the correct camp.

 

[nvx1977]

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.

If the car is at a stop, the accelerator is all the way up (relative to the floor). So first depress of the accelerator moves the car. At speed, you can let go of the accelerator completely and it will return to that same point. But now the car is in regen.

 

[nvx1977]

@MXWing: no need to respond to JeffC. This was an old post that got resurrected recently and then again very recently. OP is no longer active around here it seems.

 

[MXWing]

@novox77

Thanks.

Saw the OP that came out swinging about education and ignorance. Wish I saw that two years ago. Oh well if @JeffC decides eventually if he want's some he can come get some.

 

[Krazaak]

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.

Depends on where you’re driving. The only place I usually deal with snow down here is up in the mountains where regen makes a huge difference. My last trip, 95% of the trip was clear roads with the occassional ice patch.

I agree though that it would get minimal use, especially from people used to automatics.

 

[Zippy_EV]

I know the thread is really old and recently resurrected but JeffC does make an interesting point...

I have plenty of seat time on racetracks and after reflecting would love to have a software setting to determine the regen pedal. How great it would be to have the option to move regen to the brakes for the additional control?!?! (I'd do it despite the fact I enjoy single pedal driving.) What a neat benefit of drive by wire.

 

[scaesare]

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.

It feels like the accelerator position is mapped to a torque request. Based on current state, that determines power request.

Thus at 0 MPH any pedal position > 0% is a positive torque request, and thus a positive power request.

At 60 MPH, if you drop the pedal back down to 5%, the torque request becomes less than your current cruising torque demand, and thus there is ramped demand downwards (regen) to your requested torque level. The downward ramp appears to attempt constant time up to a g-force cutoff point (I've heard 0.3g?). That is, the car will ramp downwards faster (i.e. regen more), the greater the delta between currend and requested torque, up to a max deceleration rate.

(all of the above seat-of-the-pants observation)

Does that answer?

 

[mongo]

It feels like the accelerator position is mapped to a torque request. Based on current state, that determines power request.

Thus at 0 MPH any pedal position > 0% is a positive torque request, and thus a positive power request.

At 60 MPH, if you drop the pedal back down to 5%, the torque request becomes less than your current cruising torque demand, and thus there is ramped demand downwards (regen) to your requested torque level. The downward ramp appears to attempt constant time up to a g-force cutoff point (I've heard 0.3g?). That is, the car will ramp downwards faster (i.e. regen more), the greater the delta between currend and requested torque, up to a max deceleration rate.

(all of the above seat-of-the-pants observation)

Does that answer?

Thanks. That helps, I was pretty sure it wasn't a fixed power mapping, but wanted confirmation.

 

[daniel]

It feels like the accelerator position is mapped to a torque request. Based on current state, that determines power request.

Thus at 0 MPH any pedal position > 0% is a positive torque request, and thus a positive power request.

At 60 MPH, if you drop the pedal back down to 5%, the torque request becomes less than your current cruising torque demand, and thus there is ramped demand downwards (regen) to your requested torque level. The downward ramp appears to attempt constant time up to a g-force cutoff point (I've heard 0.3g?). That is, the car will ramp downwards faster (i.e. regen more), the greater the delta between currend and requested torque, up to a max deceleration rate.

(all of the above seat-of-the-pants observation)

Does that answer?

Except that the amount and direction of torque being requested is dependent on both pedal position and current vehicle speed. A pedal position that asks for a little bit of negative torque when going 80 mph will ask for a lot of positive torque if the car is going 10 mph.

 

[diamond.g]

Based on the power meter in my Volt, would it be better to say you are asking for a certain amount of kW more so than torque? If it take 23kW to maintain 55 mph and I reduce the power to 0 kW am I actually generating negative torque (in regen)? The meter would indicate that I am asking for 0 kW and not putting anything into the battery or out of the battery.

 

[mongo]

Based on the power meter in my Volt, would it be better to say you are asking for a certain amount of kW more so than torque? If it take 23kW to maintain 55 mph and I reduce the power to 0 kW am I actually generating negative torque (in regen)? The meter would indicate that I am asking for 0 kW and not putting anything into the battery or out of the battery.

Assuming the meter goes negative, 0 kW should be like neutral, no power in/ no power out (electrically), and deceleration is due to mechanical/ aerodynamic drag.

 

[daniel]

Based on the power meter in my Volt, would it be better to say you are asking for a certain amount of kW more so than torque? If it take 23kW to maintain 55 mph and I reduce the power to 0 kW am I actually generating negative torque (in regen)? The meter would indicate that I am asking for 0 kW and not putting anything into the battery or out of the battery.

I know nothing about the Volt. But regen by definition is using the kinetic energy of the moving car to power the motor as a generator. This generates torque against the motion of the car and generates electricity which re-charges the battery

If you are neither taking energy from the battery or putting power back in, then you are not using regen and are not generating any torque. Your car's speed is only influenced by factors such as wind resistance, slope, and friction.

 

[diamond.g]

Assuming the meter goes negative, 0 kW should be like neutral, no power in/ no power out (electrically), and deceleration is due to mechanical/ aerodynamic drag.

Okay, just wanted to make sure I was following, and yes my Volt does show regen as a negative value.

 

[scaesare]

Except that the amount and direction of torque being requested is dependent on both pedal position and current vehicle speed. A pedal position that asks for a little bit of negative torque when going 80 mph will ask for a lot of positive torque if the car is going 10 mph.

I don't believe so.. The torque request doesn't change as a result of speed/direction. The power required to achieve that request is dependent on current speed.

That's why I said:
" Based on current state, that determines power request."

For example: 0% pedal is always 0% torque. In that case the only change can be a negative one if you are moving.

25% pedal may be 40% torque. That can generate either a postivie or negative power request, based on your current vehicle state (speed/direction), but the torqu request is a static 40% every time the pedal is at that position.

 

[Rocky_H]

For example: 0% pedal is always 0% torque. In that case the only change can be a negative one if you are moving.

25% pedal may be 40% torque. That can generate either a postivie or negative power request, based on your current vehicle state (speed/direction), but the torqu request is a static 40% every time the pedal is at that position.

No, these things aren't true. Maybe it's just some misunderstanding of what the terms mean. Torque is applying force onto the drive axle. 0 torque is what is referred to as "neutral" or "coasting". There is no forward or backward force being applied. That can be accomplished at any speed or lack of speed by moving the shifter to Neutral to take it out of gear. Then the pedal position doesn't matter. But with it in Drive, the pedal position changes that, and it is mapped differently at different speeds, not static, as you say. When you are moving at some speed, you have to partially press the pedal some to get to that 0 torque, neutral type of position. Any less than that, and it is applying reverse torque to slow the car even more than coasting would. But at rest, the mapping is different. You don't have to hold the pedal partway in to keep it at rest with 0 torque or pull farther back to apply negative torque to make the car go backward. That would be a static mapping. Instead, when the car is not moving, you can have your foot all the way off the pedal, and that is applying 0 torque. There is no negative torque application in the pedal map at that point. The pedal is only 0 and up.

Slot car controllers (for the old folks) had fixed mapping, and could be made to have that negative torque in there. They had some negative torque at the full release of the trigger for braking while coming up to a curve, and you had to keep the trigger held a little to keep the car from driving backward if you wanted it to sit still.

 

[FlyF4]

I test drove the i3 and found it regened heavily off throttle.?
.

You must have been going under about 30 mph to notice heavy regen. In all Teslas the amount of the regen and deceleration depends on the speed ;-) It is greatest at the lower end of the speed.

 

[daniel]

I don't believe so.. The torque request doesn't change as a result of speed/direction. The power required to achieve that request is dependent on current speed.

That's why I said:
" Based on current state, that determines power request."

For example: 0% pedal is always 0% torque. In that case the only change can be a negative one if you are moving.

25% pedal may be 40% torque. That can generate either a postivie or negative power request, based on your current vehicle state (speed/direction), but the torqu request is a static 40% every time the pedal is at that position.

There's a thought experiment:

In a Tesla, from a stand-still, move the pedal to 50% and hold it there. The car will rapidly accelerate to some speed, and then it will hold steady at that speed. At first it's applying a lot of torque to accelerate. Once it's reached that set speed, it's only applying enough torque to overcome wind resistance and friction.

The same will apply if you move the medal to 25% or to 10%.

Now, from that 50% pedal position, traveling on the highway (and with nobody behind you) release the pedal to 25%. The car will enter regen, applying negative torque (or simply torque in the opposite direction) until the car has slowed to some lower speed, and then the torque will change to positive, to keep the car going at that slower speed. In this case, starting from highway speed and then reducing pedal position, it becomes clear: Positive torque to keep the car going at 50% pedal position, becomes regen (negative torque) with the pedal at 25%, but once the car has slowed down, it goes back to positive torque to maintain the new, slower, speed.

 

[scaesare]

No, these things aren't true. Maybe it's just some misunderstanding of what the terms mean. Torque is applying force onto the drive axle. 0 torque is what is referred to as "neutral" or "coasting". There is no forward or backward force being applied. That can be accomplished at any speed or lack of speed by moving the shifter to Neutral to take it out of gear. Then the pedal position doesn't matter. But with it in Drive, the pedal position changes that, and it is mapped differently at different speeds, not static, as you say. When you are moving at some speed, you have to partially press the pedal some to get to that 0 torque, neutral type of position. Any less than that, and it is applying reverse torque to slow the car even more than coasting would. But at rest, the mapping is different. You don't have to hold the pedal partway in to keep it at rest with 0 torque or pull farther back to apply negative torque to make the car go backward. That would be a static mapping. Instead, when the car is not moving, you can have your foot all the way off the pedal, and that is applying 0 torque. There is no negative torque application in the pedal map at that point. The pedal is only 0 and up.

Slot car controllers (for the old folks) had fixed mapping, and could be made to have that negative torque in there. They had some negative torque at the full release of the trigger for braking while coming up to a curve, and you had to keep the trigger held a little to keep the car from driving backward if you wanted it to sit still.

You know... you are right... I didn't use the correct terminology there... thanks for pointing that out.

What I should have said is that it feels like throttle position is mapped to a torque target, and then torque demand is calculated based on vehicle state. That indeed will be a variable torque value (negative being regen) that will ramp to that target.

Again, at least that's what it feels like to me...

 

[scaesare]

There's a thought experiment:

In a Tesla, from a stand-still, move the pedal to 50% and hold it there. The car will rapidly accelerate to some speed, and then it will hold steady at that speed. At first it's applying a lot of torque to accelerate. Once it's reached that set speed, it's only applying enough torque to overcome wind resistance and friction.

The same will apply if you move the medal to 25% or to 10%.

Now, from that 50% pedal position, traveling on the highway (and with nobody behind you) release the pedal to 25%. The car will enter regen, applying negative torque (or simply torque in the opposite direction) until the car has slowed to some lower speed, and then the torque will change to positive, to keep the car going at that slower speed. In this case, starting from highway speed and then reducing pedal position, it becomes clear: Positive torque to keep the car going at 50% pedal position, becomes regen (negative torque) with the pedal at 25%, but once the car has slowed down, it goes back to positive torque to maintain the new, slower, speed.

Yeah. I was using "demand" to imply that a specific throttle position always called for a specific torque value to be applied... but that's only true after the car accelerates or regens to arrive at that point. The ramp to that point will indeed be variable.

In my reply to @Rocky_H I modified what I was trying to say.

Thanks @daniel .

 

[daniel]

I really think pedal position is mapped to a target speed, not to a target torque. Of course, this is just my impression. I could be full of beans.