Why Does The Model 3 Not Use Regen When Using the Brakes.

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msjulie

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#21
In terms of that particular argument/debate, perusing the forums reveals that it seems there is a consensus that your range is increased via the one-pedal / high-regen setting


I took a class about e-car building, etc and we were presented info from a study - regen was found to only increase range when the road course called for actual braking. The point was that recapturing energy on downhills did not recover more energy than letting the car speed up more on the downhill while coasting. Seems obvious I guess that you never recapture what it cost to get moving 100%

Regardless, 1 pedal driving is great and I love that I'm not wearing the brake pads down nearly as much as otherwise...
 

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#22
Great thread. Am I understanding that when the accelerator is released on th M3, regent starts, then when the brake pedal is depressed regent stops? Or does regen continue and the brakes work separately adding friction resistance through the brake pads. I’ve had this question since the consumer reports evaluation. I was surprised, assuming that there would be two systems simultaneously working to bring the car to a stop.
 

garsh

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#23
Great thread. Am I understanding that when the accelerator is released on th M3, regent starts,
Regen begins sooner than that. Regen is at its maximum when you completely release the accelerator.
then when the brake pedal is depressed regent stops? Or does regen continue and the brakes work separately adding friction resistance through the brake pads
It's the latter. Regen continues as you press the brake pedal.
 
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Blee

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#24
Regen begins sooner than that. Regen is at its maximum when you completely release the accelerator.It's the latter. Regen continues as you press the brake pedal.
Thanks. That adds to my surprise on the lackluster breaking distance. You would think there would be a distinct advantage built in.
 
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garsh

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#25
Thanks. That adds to my surprise on the lackluster breaking distance.
The braking distance issue was due to bad ABS calibration. It has since been fixed by an OTA update.

But also, braking distance has little to do with regen. Panic braking performance is due to the physical brakes, pads, and the ABS system that controls them at the limit.
 

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#26
I took a class about e-car building, etc and we were presented info from a study - regen was found to only increase range when the road course called for actual braking. The point was that recapturing energy on downhills did not recover more energy than letting the car speed up more on the downhill while coasting. Seems obvious I guess that you never recapture what it cost to get moving 100%
This is depends on the height of the "hills" in question. If you get into say the Rockies you're dealing with hills (that the rest of the country would call mountains) where it's not really a good idea. You'll be slowing down a lot, so time's a issue, and you'd be pushing a lot of wind and probably driving at unsafe speeds due to the drastically reduced braking distance of high grade slopes. Basically, you should be modestly braking the whole way down. Which the Model 3 will with just normal 1-pedal mode. It'll handle %15 grade no problem without using the friction braking because, at least the testing I've seen, the standard regen pulls about 0.16G. The % of the slope is directly a match to the % of 1G that you'd accelerate naturally down the slope.
 

garsh

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#27
This is depends on the height of the "hills" in question.
Yes, you are of course correct. Don't speed excessively just for efficiency's sake. Safety is more important.

The basic rule is:
  • Friction brakes are least efficient. All kinetic energy is just converted to heat.
  • Regen is better, because it captures some (~60%) of that otherwise wasted kinetic energy
  • Coasting is best as you keep all of that kinetic energy
    • Caveat: unless you're going fast enough that aerodynamic losses dominate (150+ mph). Slow down.
 

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#28
The braking distance issue was due to bad ABS calibration. It has since been fixed by an OTA update.

But also, braking distance has little to do with regen. Panic braking performance is due to the physical brakes, pads, and the ABS system that controls them at the limit.
Panic one time braking distance is only a function of ABS and tires (I’ve learned recently from TMC forums). Any modern disc brake is plenty capable of driving the tires to their traction limit. Performance brakes only make a difference in repeated very hard stops. I.e. racetracks.

Interestingly, Elon said regen on the AWD vehicle’s will be capable of braking force enough to ride the tire traction limit on the 18’s. I wonder how that will be implemented?
 

garsh

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#29
Panic one time braking distance is only a function of ABS and tires (I’ve learned recently from TMC forums). Any modern disc brake is plenty capable of driving the tires to their traction limit. Performance brakes only make a difference in repeated very hard stops.
The "lackluster braking performance" discovered by Consumer Reports occurred in a "repeated panic stops" testing situation.
 

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#30
The "lackluster braking performance" discovered by Consumer Reports occurred in a "repeated panic stops" testing situation.
What it seems like from the bits I've gathered is that the ABS algorithms were designed for normal "real world" use and that the testing environment is an atypical input that lead the systems automatic re-calibration to make poor choices. It's sort of the inverse of the technique of cheating by designing to the review benchmarks.
 

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#31
I'm not sure I see strong evidence for or against the OP's assertion so far in this thread. Consider one possible advantage of disabling the regen during hydraulic braking: to allow the ABS to do its job. In a slippery ice situation, regen by itself might generate enough torque to cause a wheel to start to slip. If regen is disabled, then the ABS has full authority over wheel slip. With regen, ABS authority would be slightly more limited.
 

Maevra

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#32
I'm not sure I see strong evidence for or against the OP's assertion so far in this thread. Consider one possible advantage of disabling the regen during hydraulic braking: to allow the ABS to do its job. In a slippery ice situation, regen by itself might generate enough torque to cause a wheel to start to slip. If regen is disabled, then the ABS has full authority over wheel slip. With regen, ABS authority would be slightly more limited.
Good point! Tesla actually does mention that strong regen may cause slippage in icy conditions for this very reason, so guess that's one more plus for the not having regen on hydraulic braking.
 

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#33
The "lackluster braking performance" discovered by Consumer Reports occurred in a "repeated panic stops" testing situation.
The problem even occurred the next day. And it was fixed by removing a bug in the ABS calibration software.

My point is that better brakes do not have any effect whatsoever on stopping distances (panic or otherwise) in normal driving, only at the track.
 

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#34
Because it seems to me what's really happening in "standard" (higher) regen mode, is that you're actually having to put energy into the rotor/motor, which is set for more resistance in standard mode, so that you have to overcome that regen resistance in order to get the car to move. In a sense, you're using battery energy to turn the rotor, which is harder to turn because you've set the regen higher, but you're actually simultaneously returning energy to the battery because, well because you're regenerating at the same time. The car doesn't move forward until you've put more energy into turning the rotor than the regen resistance.
You are way over thinking this. The accelerator position is just an electronic input. The motor controller will either be in regen or power mode, at no point is it fighting itself. Low regen will only give you less regeneration all of the time you are off the accelerator, even when braking. In either mode you will have to keep a minimal throttle position to try and "coast" where you try to hit that sweet spot with minimal power or regeneration.
 

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#35
The worst is when you're braking down a steep road to just maintain speed, and you hit a pothole or other bump. The ABS kicks on for a second. When that happens, the car turns off regen altogether. It wouldn't be so bad, except the regen stays off until you take your foot off the brake pedal. So the end result is that whenever you hit a bump on a steep downhill, the car begins to accelerate. NOT AT ALL the type of behavior you want in that situation.
The Prius would do something similar with the blended brake. Hit a bump on a downhill and regen would stop and it would take a moment for the friction brakes to kick in. For a brief moment it feels out of control and your heart jumps into your throat. Largest problem is that this exact scenario occurs on our road about a quarter mile from our house and it was the wife's car so I would only drive frequently enough to forget about this little issue until my next minor heart attack.
 

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#36
The Prius would do something similar with the blended brake. Hit a bump on a downhill and regen would stop and it would take a moment for the friction brakes to kick in. For a brief moment it feels out of control and your heart jumps into your throat.
I know this exact feeling in my Prius, but I'm fairly certain it's all ABS and not the regen. The regen is so weak in the Prius, and it's effectively nil below 20 mph. I'm pretty sure you wouldn't notice if it wasn't working at low speed. There's a place where I hit a pothole right before exiting a parking lot. When the front wheel hits it, I think the ABS takes charge and removes all braking for a fraction of a second. It's pretty shocking when it happens. First time, I thought I got rear-ended.
 

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#37
I know this exact feeling in my Prius, but I'm fairly certain it's all ABS and not the regen. The regen is so weak in the Prius, and it's effectively nil below 20 mph. I'm pretty sure you wouldn't notice if it wasn't working at low speed. There's a place where I hit a pothole right before exiting a parking lot. When the front wheel hits it, I think the ABS takes charge and removes all braking for a fraction of a second. It's pretty shocking when it happens. First time, I thought I got rear-ended.
Yeah, we've owned 3 Priuses (Prii?) and the ABS software—in my opinion, at least for model years 2008, 2009, the best years—is janky and scary at times. Any time a wheel is jarred by a bump or pothole, breaking is effectively disabled for a second or two. No bueno.
 

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#38
A friend just drove his model S 100D up Pikes Peak yesterday. He said he used 30% of the battery getting to the top and regained 10% when he got back to the bottom. I would have expected more than 10% to be added back during the decent, but regen must have been doing most of the deceleration on the way down because his brake temperature at the checkpoint on the way down was only 77 degrees.
 

fsKotte

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#39
You are way over thinking this. The accelerator position is just an electronic input. The motor controller will either be in regen or power mode, at no point is it fighting itself. Low regen will only give you less regeneration all of the time you are off the accelerator, even when braking. In either mode you will have to keep a minimal throttle position to try and "coast" where you try to hit that sweet spot with minimal power or regeneration.
Not sure if I'm really over-thinking it actually. The electronic input isn't behaving like a binary switch. It isn't regen ON or regen OFF.

Instead, it's behaving like a rheostat, where the regen is increased/decreased depending on how much pressure you're putting on the pedal. This effect is borne out by the many folks who talk about "feathering" the accelerator to modulate their speed. This is clearly evident when you're in "one pedal" mode. If you're going a certain speed, and you *slightly* pull back on the accelerator input, the car slows a little, and regen is a little. But if you totally take your foot off the accelerator, then the regen kicks in very severely and it's like you've put on the brakes suddenly, and the green regen bar goes farther out.

So, either the regen resistance is being modulated, or regen resistance is constant and the balance between your battery power going to turn the rotor is being offset by the regen resistance, and the modulating of the pedal is simply altering that balance by modulating the amount of power being used to try to turn the rotor. Your modulating the amount of battery power you're putting into the system is being offset by the regen resistance. From how the car is behaving in "one pedal" mode when I drive it, this seems to be what's happening.
 

garsh

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#40
So, either the regen resistance is being modulated, or regen resistance is constant and the balance between your battery power going to turn the rotor is being offset by the regen resistance, and the modulating of the pedal is simply altering that balance by modulating the amount of power being used to try to turn the rotor. Your modulating the amount of battery power you're putting into the system is being offset by the regen resistance. From how the car is behaving in "one pedal" mode when I drive it, this seems to be what's happening.
Your explanation makes it sound like there are two opposing forces - power turning the rotor, and "regen resistance". This is not true. The motor is either generating power, or it's receiving power. At no point in time is the battery both putting power into the motor, AND accepting power from regen. It's one or the other.