[deepskier]

Usually in travel assist, if I manually brake it's a light tap to turn off the system so I can coast.

However I've had a few times when I've needed to manually brake firmly and immediately while travel assist was active, and it felt like I got no regen and went directly to friction brakes. No movement in the green bar either, also indicating no regen. Regen was definitely available and it kicked in with the next application of the brake pedal.

Anyone else experience this?

 

[ericy]

Usually in travel assist, if I manually brake it's a light tap to turn off the system so I can coast.

However I've had a few times when I've needed to manually brake firmly and immediately while travel assist was active, and it felt like I got no regen and went directly to friction brakes. No movement in the green bar either, also indicating no regen. Regen was definitely available and it kicked in with the next application of the brake pedal.

Anyone else experience this?

Yeah, I have noticed this as well. I dont know if this is a big or feature.

 

[Perfesser]

I have observed this, too. My best guess: the first part of the brake pedal travel gets you regen and, at a certain point, regen stops and you get friction braking. I doubt that there is any special programming for brake settings in travel assist mode, but it's logical that if you hit the brakes "firmly and immediately" you probably passed through the regen portion of the pedal travel so fast that it does not register any regen. I have always thought there is a little lag in the green regen bar, as if it is reporting the regen you collected a second earlier. FWIW, I'm quite satisfied with the way VW has handled the transition from regen to friction braking.

 

[Nai3t]

If you haven't seen it, check out this document outlining the ID.4 braking system: https://static.nhtsa.gov/odi/tsbs/2021/MC-10189711-0001.pdf

Hydraulic braking is computer controlled. The foot pressing the pedal is responsible for only about 12% to 14% of the hydraulic braking force via direct input, under normal operation. Braking input is read by the computer, which then blends appropriate amounts of regen and friction braking based on demand and battery condition.

I mention this only to point out that even if the driver stomps on the brakes in panic stop type scenario, the computer is right there all along, and although VW says their hydraulic booster is fast, I suspect calling for regen is equally rapid, so I can't see the system calling for one but not the other.

So I'm really curious why this is the case that you all are noticing this! Could it be that applying full hydraulic braking is more consistent than regen so the system prioritizes it over blending friction + regen. Full hydraulic should have more than enough power to lock up the brakes (anti-lock is going to kick in anyway)?

 

[ericy]

I have observed this, too. My best guess: the first part of the brake pedal travel gets you regen and, at a certain point, regen stops and you get friction braking. I doubt that there is any special programming for brake settings in travel assist mode, but it's logical that if you hit the brakes "firmly and immediately" you probably passed through the regen portion of the pedal travel so fast that it does not register any regen. I have always thought there is a little lag in the green regen bar, as if it is reporting the regen you collected a second earlier. FWIW, I'm quite satisfied with the way VW has handled the transition from regen to friction braking.

It is specific to having travel assist on - if you press the brake pedal, you seem to get no regen at all. But once you come to a stop and start driving again, you again get regen when you use the brake pedal.

 

[Tinman]

Could it be that applying full hydraulic braking is more consistent than regen so the system prioritizes it over blending friction + regen. Full hydraulic should have more than enough power to lock up the brakes (anti-lock is going to kick in anyway)?

I think you may be onto something. Or, I'm not onto anything. Could the regen be too inconsistent (full battery/cold battery, etc.) for ABS to predict or too slow to release the wheel back to true ground speed for ABS to control its magic? I'm afraid this doesn't answer the, "It is specific to having Travel Assist on" above, though. I've not consciously noticed this...yet.

 

[Nai3t]

I suppose the next test would be to check if the behavior repeats during a non - TA panic stop.

I'll tell you, in my '17 i3 it's disconcerting when I'm braking heavily and hit a pothole or some other surface irregularity. The regen instantly cuts off because the wheel speed sensors detected a lock - up, and it feels almost like the car is accelerating for a moment while I press the brake pedal in harder to make up for my lost stopping force.

Supposedly this particular behavior was addressed in the subsequent model year with higher sampling wheel speed sensors, but it serves to demonstrate the point that the method for modulating a wheel lock situation is different for a hydraulic system vs. electric resistance, or that's even an ability of our vehicles. (Anybody know?)

 

[ID.Furkan]

i believe if you brake for no apparent reason [read: the sensors are not sensing any reason to brake at all] and you press the brake "quick/Hard" instead of gliding the brake pedal the brakes gets in an "alert" state instantly.

so full front brake = full body weight at front axle = almost no rear grip = no regen needed = so cutting "power"/free wheeling.

Happend enough times for me to feel the difference.. dont know if its a bug or an safety thing. 1 thing i know is that the brakes are working when needing them. with or without regen.

 

[igniztion]

I think it's related to ACC, not just TA. Sometimes when the car has started braking (regen) to slow down because of a car in front or intersection, I feel the car isnt slowing down enough and press the brake pedal. In this scenario, sometimes the regen stays at the same, relatively low level, and hydraulic brakes are used.

I assumed it was programmed that way so that the brake pads and discs are actually used every so often to avoid them rusting to pieces.

 

[Huey52]

Could very well be. Also related one reason we have rear drum brakes as being somewhat encapsulated they are more protected from the elements, which is important given how little they're used.

I think it's related to ACC, not just TA. Sometimes when the car has started braking (regen) to slow down because of a car in front or intersection, I feel the car isnt slowing down enough and press the brake pedal. In this scenario, sometimes the regen stays at the same, relatively low level, and hydraulic brakes are used.

I assumed it was programmed that way so that the brake pads and discs are actually used every so often to avoid them rusting to pieces.

 

[Nai3t]

I

I assumed it was programmed that way so that the brake pads and discs are actually used every so often to avoid them rusting to pieces.

There's a direct link from pedal to hydraulics, so at minimum the pads ought to be wiping rotors every press or the brake.

I'm convinced now this is probably an anti lock thing. Since my last post on this thread I've found a bunch of research papers (Google search) from 2008 to current looking into coordinated or combined braking, mentioning specifically the problem that hydraulics are needed for ABS modulation. The papers purpose different techniques to make these systems play nice together, since overuse of regen can lead to tire to slip.

 

[deepskier]

I should have said 'brake normally', the behavior doesn't require hard application of the brakes. I've adjusted my breaking habits to reach max regen quickly and not exceed the regen limit.

That's another topic... If you get to max Regen at say 45mph, with steady brake position, by the time you have slowed to 35mph, the Regen level is only 50 to 60%. You have to increase brake force to keep constant Regen. This is a programming choice by VW, and one I would prefer didn't back off as much.