Driver + Regen Braking

[R1Sky Business]

When using adaptive cruise control or highway assist, is the braking entirely Regen braking or is there help from mechanical brakes?

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[RexRemus]

Regen unless that's not enough, at which point friction brakes will be blended in

 

[R1Sky Business]

Regen unless that's not enough, at which point friction brakes will be blended in

Not enough meaning a sudden braking scenario....

 

[RexRemus]

Possibly but that would get into collision mitigation system territory but it would absolutely use the friction brakes for that.

But "not" enough could just be a large enough speed delta between you and the car in front of you that it exceeds the ability of regen alone to be able to keep a safe following distance - it might not be "sudden" it could develop gradually as in the driver ahead is braking for an exit but they underestimate the distance and must brake harder than expected - this would potentially be "aggressive" deceleration, it might happen in multiple stages, but it would not be "emergency stop" conditions - they still end up at 35-45 mph for the exit. But it might mean an aggressive drop from 85-45 that begins as a gentle drop from 85-70 and a harder drop from 70-45.


Not trying to be nit-picky about the differences or whatever, just still saying if the vehicle has a need to slow down, it uses regen until regen isn't enough and then it adds friction brakes - that could be because collision avoidance kicks in, or any other safety system that can trigger such a thing. But if/when the vehicle deems it necessary to "slow down" and regen isn't cutting it, brakes get added.

Is there some specific scenario you're worried about? If so why not just explain it so others can validate/test?

 

[R1Sky Business]

Possibly but that would get into collision mitigation system territory but it would absolutely use the friction brakes for that.

But "not" enough could just be a large enough speed delta between you and the car in front of you that it exceeds the ability of regen alone to be able to keep a safe following distance - it might not be "sudden" it could develop gradually as in the driver ahead is braking for an exit but they underestimate the distance and must brake harder than expected - this would potentially be "aggressive" deceleration, it might happen in multiple stages, but it would not be "emergency stop" conditions - they still end up at 35-45 mph for the exit. But it might mean an aggressive drop from 85-45 that begins as a gentle drop from 85-70 and a harder drop from 70-45.


Not trying to be nit-picky about the differences or whatever, just still saying if the vehicle has a need to slow down, it uses regen until regen isn't enough and then it adds friction brakes - that could be because collision avoidance kicks in, or any other safety system that can trigger such a thing. But if/when the vehicle deems it necessary to "slow down" and regen isn't cutting it, brakes get added.

Is there some specific scenario you're worried about? If so why not just explain it so others can validate/test?

Just curious

 

[zefram47]

That's always been unclear since the brake pedal does move when using ACC and the truck slows down at all, say going down a hill. I really hope it's not using the friction brakes since that is usually unnecessary in most situations. Note, Rivian did add the regen assist feature (bottom of the Driver+ settings, IIRC) that *will* blend in friction brakes if there is a regen limit due to temperature or other factor. They do that transparently and no longer show the regen limitation if the feature is on. With all the hills/mountains I have around here, I keep that feature OFF so I know what is going on.

 

[srkz]

I suspect that Driver+ is handled entirely by the Mobileye SoC and since Rivian doesn't have blended braking they're using mechanical brakes to play nicely with this "off the shelf" ADAS system. You can feel the brake pedal moving when Driver+ makes speed adjustments, and the brake pedal is mechanically linked to the master cylinder (no blended braking.)

Tesla is the only other OEM that doesn't have blended braking, but they rolled their own ADAS so presumably they figured out how to use regen to moderate the speed. Every other OEM uses blended braking so even if they're using an off the shelf Mobileye system for ADAS the "brake" command always blends regen in first. I think Rivian is the only EV OEM that uses an off the shelf Mobileye SoC for ADAS but also doesn't have any blended braking.

I've read at least one anecdote from an owner that spent a majority of time in Driver+ and also had to replace worn out brake pads which should basically never happen in an EV, so I'm personally thinking it's always mechanical braking when needed in Driver+.

One easy way to test this would be to start at the top of a hill with cold brakes, set cruise control, descend the hill or mountian, and then check the temperature on the rotors - if they're hot then Driver+ doesn't use regen.

I do live at the top of a hill... brb.

 

[srkz]

Yep, I just tested it and I can confirm that Driver+ does not use regen at all, it uses purely mechanical friction brake pads to modulate speed.

I started at the top of a hill with cold (ambient temp) brake rotors, accelerated to 50 going downhill and set cruise control. I continued downhill on cruise control losing about 400 feet of elevation over roughly 1.25 miles. I rested my foot lightly on the brake pedal and felt it modulating the brakes to control my speed. The brake pedal is mechanically linked to the friction brakes so there is no regen blended in. Near the bottom of the hill I disengaged cruise control and allowed regen to bring me to a stop. I immediately got out and tried to touch the brake rotors but they were too hot to touch, I'd estimate over 130 degrees F.

Ergo, we can conclude that cruise control does not use regen on the R1 platform.

Don't use Driver+ too much if you live on a hill and care about your brake pad life!

 

[SwampNut]

Yep, I just tested it and I can confirm that Driver+ does not use regen at all, it uses purely mechanical friction brake pads to modulate speed.

I started at the top of a hill with cold (ambient temp) brake rotors, accelerated to 50 going downhill and set cruise control. I continued downhill on cruise control losing about 400 feet of elevation over roughly 1.25 miles. I rested my foot lightly on the brake pedal and felt it modulating the brakes to control my speed. The brake pedal is mechanically linked to the friction brakes so there is no regen blended in. Near the bottom of the hill I disengaged cruise control and allowed regen to bring me to a stop. I immediately got out and tried to touch the brake rotors but they were too hot to touch, I'd estimate over 130 degrees F.

Ergo, we can conclude that cruise control does not use regen on the R1 platform.

Don't use Driver+ too much if you live on a hill and care about your brake pad life!

If this is true, it could be the most retarded thing I've ever read, and another ridiculous disappointment compared to Tesla AP.

But a point, it MAY use regen, but also mechanical. Though it seems less likely. Wait, there's a display for this, showing power out and in. Did you watch that?

 

[srkz]

If this is true, it could be the most retarded thing I've ever read, and another ridiculous disappointment compared to Tesla AP.

But a point, it MAY use regen, but also mechanical. Though it seems less likely. Wait, there's a display for this, showing power out and in. Did you watch that?

Yes, the display showed the same amount of "regen" that it normally does when I'm going down the hill without cruise control, but that display doesn't really mean anything anymore.

Ever since they included the "Regen Assist" feature some updates ago they don't really show you an accurate display of regen in the gauge cluster anymore. It's more of a gauge of your total acceleration and deceleration. Even if you're at 100% state of charge going down a mountain and your regen is severely limited and the braking is almost entirely friction from Regen Assist, it will still show the power bar like normal with no indication that you're not actually getting that regen back into the HV battery pack.

For this test I had Regen Assist turned off, and there shouldn't have been any reason to limit my regen. As soon as I disengaged cruise control towads the bottom of the hill and actual regen turned back on, I felt the brake pedal relax and the vehicle started slowing down considerably harder than it had been on cruise control, which would seem to imply that it had plenty of regen left in the tank and wouldn't have needed to use friction brakes all the way down the hill.

 

[SwampNut]

I still want to not believe this insanity. Truly, other than needing a truck, there is no reason for anyone to buy a Rivian over a Tesla. But that was my reason for switching.

 

[srkz]

I still want to not believe this insanity. Truly, other than needing a truck, there is no reason for anyone to buy a Rivian over a Tesla. But that was my reason for switching.

Yeah... I'm increasingly angry that it turns out Tesla really is that much better than everyone else, but I wanted a truck and I can't fucking stand how ugly they are or being in any way related to Elon.

The R1 platform looks great, and seems to be way overbuilt with all of its various off the shelf components, but the engineering required to integrate it all in a way that makes sense and just works still seems to be a bit of amateur hour.

 

[SwampNut]

You'd find me RUNNING to pick up a CT if it were available. I don't give one damn about the petulant man-child running Tesla. I sure miss the fact that I let my Tesla drive itself 98% of the time.

 

[Mellowyellow]

I can also confirm this anecdotally. I drove the same 100 mile stretch of highway 4 times in a week and my efficiency numbers with Driver+ are significantly lower.

 

[Kidentist]

So don't use Driver + going downhill.......got it! how about "simple" cruise control??

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