Weird/dangerous ACC/regen braking behavior
- Thread starter victor_2019
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CJC
Well-Known Member
I have read more than a few of those sort of stories on the UK Kona EV forum. Scary experience for you, but like you I am glad no one was tailgating you.
Esprit1st
Well-Known Member
Again: SCC/ACC is not designed to brake for stopped objects! It is designed to follow traffic and slow down with it (all the way to a stop if you have the ultimate version US). Just like the Tesla accidents where the autopilot didn't brake for the barrier or a stopped car.
Also the automatic emergency braking only works up to a certain speed (Not sure which).
It is important to understand the limitations of these systems.
So if you still use your SCC when you're on the off ramp and approaching stopped traffic you're playing with fire. I always deactivate it on the off ramp and use the paddle to decelerate. The adaptive Regen does the rest once you get closer to stopped traffic.
Although it's a nice game to try to time the paddle press exactly, you don't let it go and come to a stop at the perfect distance behind the car in front of you. [emoji12][emoji38]
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victor_2019
Active Member
No, that's not what i said, read the original message again.
Regen didn't work.
I never said the mechanical brakes didn't work, i said they weren't as strong as i expected, the force was less than regen level 3.
Someone asked how come i was able to stop if mechanical brakes were not as strong as level 3 regen and i said level 3 regen is already quite strong so having mechanical brakes less strong than that doesn't imply the car won't be able to stop.
The brakes work fine now. I doubt this is a mechanical problem, it's an electronic problem.
The brakes and regen is controlled by a brake controller which decides how to blend the regen braking and the mechanical brake.
It will ask for increasing regen and then will start to add mechanical brakes in the equation.
But if the regen braking it requests is not there, the force obtained from mechanical braking alone will not be strong.
It's not because the mechanical brakes are weak, it's because they are not ordered to be strong.
victor_2019
Active Member
I know ACC ignores already stopped objects, but in this case i wasn't approaching already stopped traffic, i was following cars which were slowing down while in a curve.
So it's entirely possible the radar lost track of the car in front.
What's wrong is that when i pressed the brakes there was no regen. I looked at the dash because the braking felt weak and i saw the power meter was in neutral, motor was coasting.
And no, i wasn't using the paddles.
I couldn't reproduce this after, every time i pressed the brakes after i got strong regen.
So it's entirely possible the radar lost track of the car in front.
What's wrong is that when i pressed the brakes there was no regen. I looked at the dash because the braking felt weak and i saw the power meter was in neutral, motor was coasting.
And no, i wasn't using the paddles.
I couldn't reproduce this after, every time i pressed the brakes after i got strong regen.
Esprit1st
Well-Known Member
Ok, I see. Thanks for the clarification.
BTW. When you push the brakes with your foot there is always friction brakes applied. You can test that any time you come to a stop and you just barely touch the brakes you will notice that once the car comes to a stop it will not rock back and forth like it does when you use only the paddle which uses Regen only.
Maybe there was some rust on your brake discs because you didn't use them? Some people kind of brag about not using their friction brakes at all, and I'm sure if they had to rub off the rust they will have less breaking power. [emoji2369]
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BTW. When you push the brakes with your foot there is always friction brakes applied. You can test that any time you come to a stop and you just barely touch the brakes you will notice that once the car comes to a stop it will not rock back and forth like it does when you use only the paddle which uses Regen only.
Maybe there was some rust on your brake discs because you didn't use them? Some people kind of brag about not using their friction brakes at all, and I'm sure if they had to rub off the rust they will have less breaking power. [emoji2369]
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victor_2019
Active Member
I checked brake fluid, it's at max
I think the issue is electronic.
I did a test today and gradually pressed the brake.
The regen increases proportional to the pedal pressure until a point, after which the brakes engage and you can feel the harder deceleration. But the whole time there's something like 3 or 4 bars of regen in the meter, depending on speed.
When i was braking that time the power meter in the dash was in neutral, no regen bars were displayed.
I think the issue is electronic.
I did a test today and gradually pressed the brake.
The regen increases proportional to the pedal pressure until a point, after which the brakes engage and you can feel the harder deceleration. But the whole time there's something like 3 or 4 bars of regen in the meter, depending on speed.
When i was braking that time the power meter in the dash was in neutral, no regen bars were displayed.
Esprit1st
Well-Known Member
victor_2019
Active Member
Do you have a source on that from Hyundai?
Esprit1st
Well-Known Member
FloridaSun
Well-Known Member
I believe that rege
I believe that regen will always be used first before friction brakes but below about 5 mph, friction brakes are used and I would think that when you pull the regen paddle at slow speed, it actually engages the friction brakes below 5 mph but I may be wrong. We know that the car is able to engage the friction brakes for the FCA, so it may be possible that this also happens at low speed using the regen paddle.
KiwiME
Well-Known Member
Esprit1st
Well-Known Member
You are free to believe whatever you want. If you actually try it like I described you will come to the same conclusion. Why would it apply friction brakes if the actual purpose of the left paddle is to come to a stop with Regen? And the same goes the way around for the foot brake. Why wouldn't it apply a tiny amount of you touch the brakes? Worst case scenario the Regen doesn't work (as possibly in your case) you wouldn't get any breaking action at first and then some with the brake pedal. I think besides it not making sense, I believe it would be a greater engineering offer to find a way around it rather than just applying some braking action anyways.
And again, use the same testing that I did to find out yourself. The engineering effort of applying brakes when you touch the brake pedal only below a certain speed rather than at a higher speed just doesn't make sense anyways.
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victor_2019 might have felt the lower level of regen (at the bottom of IV) to the middle of the slope where the friction brake presure kicks in (V)
BTW KiwiME where did you get this and thanks for the info , service manual ?
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Esprit1st
Well-Known Member
Very interesting and honestly I didn't expect it being that way. But it most certainly explains the issue. Since he slammed on the brakes the system skipped forward to scenario IV as you mentioned. That's why he didn't get Regen.
I suspect it also explains why the car doesn't rock back and forth since the speed is almost none, so only the last part V applies in my testing.
Good to know! We never stop learning. [emoji6][emoji106]
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I suspect it also explains why the car doesn't rock back and forth since the speed is almost none, so only the last part V applies in my testing.
Good to know! We never stop learning. [emoji6][emoji106]
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I would really like to get a copy of the service manual. The dealership says info only available for service tecks only.
KonaTom
Well-Known Member
I have one but it’s for kona ICE so not much use for thisI would really like to get a copy of the service manual. The dealership says info only available for service tecks only.
KiwiME
Well-Known Member
From personal observations the only event during which the friction brakes are not used by automatic systems is the Left-Paddle-Hold, hence the rocking. When SCC stops the car in a queue for example you can sometimes hear them groan on takeoff. Ditto, Autohold.
I would wildly speculate based on my possibly-outdated 1990s engineering experience designing industrial servo motor controls for automated factory machinery is that the LPH initiates a relatively-primitive programmed deceleration curve that can only be cancelled, not modified on the fly. The motor's rotational position must match a fixed curve within a small tolerance and as such will use battery power to ensure compliance, making it possibly less-efficient than just using the brakes when going slow (lol!). That's why we are stuck with just one decel rate. At both initiation and when a full stop is approached, the deceleration rate decreases to zero giving both a fairly smooth, jolt-free entry and exit. The rocking at the end is due to what is called "deadband", an intentional programmed slack of a few degrees of rotational position where motor current is brought down to a low value to avoid winding overheating while holding position.
In future models I would not be surprised if the feature either has a variable rate depending on how far back you pull, or the function is fully integrated into the accelerator pedal.
Yes, it's fricking complicated but I think most EVs have something similar. The best thing is that you can drive the car normally without suffering a loss of economy.
To add, the reason the mechanical brakes are used at slow speeds is because of the complexity of designing servo controls that can emulate the feel of a brake pedal near a full stop and reprogram on the fly as you modulate the pedal. It's just a lot easier to do it conventionally and it eliminates the deadband feeling as well.
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From what I see here the rear brakes are strictly hydraulic while the fronts are additionally software controlled by a ball screw applying pressure in the cylinder. My guess is #7 is a valve to bypass the motor input and apply hydraulic upon emergency type activation.
Thanks so much for the diagram ( outdated 1990 engineer speculation approved)
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