Regen Braking for Beginners.... I have questions

Trandall

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I have some experience with regen deceleration in my Accord hybrid. I think the to get the greatest benefit Rivian will need at least 3 modes or regen ranges. One which truly coasts without regen to maximize efficiency, one with moderate regen to give middle ground between coasting, putting back energy and saving mechanical brakes, and one with high regen to reduce brake wear and reclaim energy when coasting is unwanted. I have found frequent driving situations where any one of the three is the best choice so hopefully Rivian will provide the means to do at least these three.





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Gshenderson

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Ouch, so round trip of 64 miles uses 87 miles of range at 79mph. wouldn't that be 36% less than Tesla's stated range. This is something I'm going to need to get used to.
Pushing it at 80mph up that mountain uses a lot of juice! My 4Runner has to drop two gears to go that fast and is running all out.
 

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Ouch, so round trip of 64 miles uses 87 miles of range at 79mph. wouldn't that be 36% less than Tesla's stated range. This is something I'm going to need to get used to.
SLC to Park City is climbing what’s probably the second most treacherous mountain pass with an interstate. I-80 through Parley’s Canyon is a huge climb on the way up, I’m surprised it’s not more tbh. No vehicle I’ve ever driven could maintain a steady 79mph higher than like 3rd gear.
 

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Once you've gotten used to one-pedal driving, strong regen instead of coast, and no creep, it's hard to go back. I was skeptical (and grew up driving manual), but Tesla's approach won me over -
  1. Braking is totally unambiguous - it actuates a physical brake and there's no mystical blending action. If you want maximum regen, don't use the brakes. If you need to stop fast, use the brakes. I very often will wrap up my entire commute without ever touching the brakes except to put the car in gear. (I really like that this encourages healthy following distances and helps smooth out stop and go, too.)
  2. Achieving maximum regen is simple: avoid unnecessary speed fluctuations, give yourself room to brake primarily via regen, only use the physical brake if you need to.
  3. While it's a little bit "lurchy" before you get used to it, with a little practice it's far easier to do "limo-style" smooth stops and incredibly graceful deceleration with one-pedal driving. The trick is to never lift off of the gas suddenly (unless you really need to) - the rapid swing from "acceleration" to "deceleration" happens way faster than it ever can in a two-pedal setup and is super uncomfortable for passengers.
One pedal combined with an excellent hill hold is also amazing in a place like Seattle - you can inch your way up the steepest hills with total precision with almost no effort. It's terrific.

Tl;dr, regen is great and any coasting or friction braking feels like such a waste of potential energy once you're used to regen. I really, really hope Rivian takes a similar approach (or at least makes it configurable - my wife hates everything I've described above.)
I understand what your saying about “Hold’’ for hilly situations and I agree. But using Creep is smart, sensible and above all else it is safer at low speeds. I record creep because I dot want anybody to be ‘’that guy’’ who runs into something or someone brocade they weren’t ‘’covering’’ the break pedal or because thus made other mistakes that so many new to electric vehicles have made. So use creep and be safe. IMHO.
 

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I have some experience with regen deceleration in my Accord hybrid. I think the to get the greatest benefit Rivian will need at least 3 modes or regen ranges. One which truly coasts without regen to maximize efficiency, one with moderate regen to give middle ground between coasting, putting back energy and saving mechanical brakes, and one with high regen to reduce brake wear and reclaim energy when coasting is unwanted. I have found frequent driving situations where any one of the three is the best choice so hopefully Rivian will provide the means to do at least these three.
I'm not sure I understand the "coast to maximize efficiency" approach here. Coasting gains nothing over the same deceleration curve in one-pedal driving. But it comes with blended braking, which offloads complexity to the driver. With blended braking, there's no wasted energy while regen is engaged, but tons of waste once you engage the physical brakes. The driver either has to actively manage/intuit the threshold between regen and physical braking to optimize recovery, or just accept that braking is more lossy than it could be. In this regime it seems like it's actually harder to maximize efficiency.

With the one-pedal approach, optimizing for efficiency is simpler and maps controls more directly to the vehicle's functions: The accelerator makes the vehicle go. At all other times (slowing/downhill/etc), the motors will regenerate any energy that they can. The driver doesn't need to do anything special to maximize the potential energy reclaimed; just tell the vehicle how fast to go, and let it "coast" to a stop at all other times. Software manages the last tiny bit of blending in physical brakes as needed to reach a complete stop. If you need aggressive/fine braking maneuvers, that's where the brake pedal comes in: A pedal which actuates friction brakes and does nothing else. Simpler, more efficient, and your brake pads last forever.

During any deceleration, missed regen is a missed opportunity. Any time the physical brakes engage, you're wasting potential energy. The "best" approach should optimize for these factors, maximizing passive regen and preserving physical brakes for actual necessity to achieve desired deceleration.
 

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SLC to Park City is climbing what’s probably the second most treacherous mountain pass with an interstate. I-80 through Parley’s Canyon is a huge climb on the way up, I’m surprised it’s not more tbh. No vehicle I’ve ever driven could maintain a steady 79mph higher than like 3rd gear.
Gotcha, so not you average incline over a rolling hill this includes a mountain pass. That gives a little more perspective.
 

Trandall

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I'm not sure I understand the "coast to maximize efficiency" approach here. Coasting gains nothing over the same deceleration curve in one-pedal driving. But it comes with blended braking, which offloads complexity to the driver. With blended braking, there's no wasted energy while regen is engaged, but tons of waste once you engage the physical brakes. The driver either has to actively manage/intuit the threshold between regen and physical braking to optimize recovery, or just accept that braking is more lossy than it could be. In this regime it seems like it's actually harder to maximize efficiency.

With the one-pedal approach, optimizing for efficiency is simpler and maps controls more directly to the vehicle's functions: The accelerator makes the vehicle go. At all other times (slowing/downhill/etc), the motors will regenerate any energy that they can. The driver doesn't need to do anything special to maximize the potential energy reclaimed; just tell the vehicle how fast to go, and let it "coast" to a stop at all other times. Software manages the last tiny bit of blending in physical brakes as needed to reach a complete stop. If you need aggressive/fine braking maneuvers, that's where the brake pedal comes in: A pedal which actuates friction brakes and does nothing else. Simpler, more efficient, and your brake pads last forever.

During any deceleration, missed regen is a missed opportunity. Any time the physical brakes engage, you're wasting potential energy. The "best" approach should optimize for these factors, maximizing passive regen and preserving physical brakes for actual necessity to achieve desired deceleration.
If I'm understanding "blended braking" then I think that's what I was trying to describe just that it wouldn't necessarily be only controlled with a pedal, could be combo of pedal & paddles on the column or selector know (preferably tactile not software). My thought on coasting for efficiency is on a long moderate decline just coast without regen loss would be preferable as long as no mechanical braking was required. Not sure if this is any clearer.
 

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I'm not sure I understand the "coast to maximize efficiency" approach here. Coasting gains nothing over the same deceleration curve in one-pedal driving. But it comes with blended braking, which offloads complexity to the driver. With blended braking, there's no wasted energy while regen is engaged, but tons of waste once you engage the physical brakes. The driver either has to actively manage/intuit the threshold between regen and physical braking to optimize recovery, or just accept that braking is more lossy than it could be. In this regime it seems like it's actually harder to maximize efficiency.

With the one-pedal approach, optimizing for efficiency is simpler and maps controls more directly to the vehicle's functions: The accelerator makes the vehicle go. At all other times (slowing/downhill/etc), the motors will regenerate any energy that they can. The driver doesn't need to do anything special to maximize the potential energy reclaimed; just tell the vehicle how fast to go, and let it "coast" to a stop at all other times. Software manages the last tiny bit of blending in physical brakes as needed to reach a complete stop. If you need aggressive/fine braking maneuvers, that's where the brake pedal comes in: A pedal which actuates friction brakes and does nothing else. Simpler, more efficient, and your brake pads last forever.

During any deceleration, missed regen is a missed opportunity. Any time the physical brakes engage, you're wasting potential energy. The "best" approach should optimize for these factors, maximizing passive regen and preserving physical brakes for actual necessity to achieve desired deceleration.
Regen is only about 50-70% efficient. Coasting down a hill and then using that momentum to avoid the throttle is much more efficient (but you are likely to exceed the speed limit). Coasting by definition means not applying slowing force by either regen or the friction brakes.

Blended brakes are not inherently more or less efficient than Teslas scheme of separating the two functions. With blended brakes, pushing on the brake pedal engages regen - the harder you push, the more regen you get. The friction brakes are only engaged when you are asking for more braking than the motors can provide (emergency braking or at slow speed). If a vehicle can come to a complete stop in one pedal driving, it is either using the friction brakes or battery power to do so since regen tails to zero as speed decreases (though minor, blended brakes can actually be more efficient).
It won't be an issue on Rivians, but 2WD vehicles only get regen from the drive wheels and this can create control issues in slippery conditions. Blended brakes sometime use the friction brakes on the non-drive wheels (usually at a reduced rate) to help with stability/control.
 
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I'm hoping Rivian blends the brakes in with one pedal driving that last little bit when coming to a stop rather than applying reverse motor current to keep the brakes clean and to hold position once stopped.
 

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Regen is only about 50-70% efficient. Coasting down a hill and then using that momentum to avoid the throttle is much more efficient (but you are likely to exceed the speed limit). Coasting by definition means not applying slowing force by either regen or the friction brakes.
Got it. I think the catch here is that it's comparing two different speed profiles. If we assume the car has cruise control on and maintains a given speed (without going over), regen is more efficient. Otherwise the "accelerating downhill coast" does make sense as a scenario where coasting is theoretically more efficient.

Blended brakes are not inherently more or less efficient than Teslas scheme of separating the two functions. With blended brakes, pushing on the brake pedal engages regen - the harder you push, the more regen you get. The friction brakes are only engaged when you are asking for more braking than the motors can provide (emergency braking or at slow speed).
This is what I'm struggling with a little bit. The thereshold between "pure regen" and "friction" is a weird thing to offload to a drive who is trying to maximize regen, versus making it a clear binary (if I push this pedal I've failed to achieve theoretical maximum regen). Of course we could go back and forth on whether gamifying delayed braking is a good incentive 😊

To be clear, when I talk about blended braking I specifically mean blended pedal function - it seems clear that some amount of software-driven friction braking is appropriate at the margins when coming to a complete stop.

I guess the good news is that at the end of the day most of this is pedantry; we're probably talking about minor efficiency differences and drivers will adapt. Subjectively, I love one-pedal and hope I get to keep it on my Rivian, but it's probably not a dispositive factor.
 

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Of note, there was a fat button on the rudimentary center control stack for the Long Way Up trucks that was labeled “one-pedal mode” or something to that effect.

They have definitely been thinking about this for a very long time.
 

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