Regen braking issues

[Sparklebeard]

The regen and friction brakes have to blend together.

Regen works very well the faster you’re going, but it’s worthless at low speeds and cannot stop the vehicle.

It’s possible you experienced the blending not working well, so the regen started to fade as you slowed down but the car misjudged how much friction brake to apply to keep the braking curve smooth

 

[Spektre]

I've been experiencing issues that I think may be related to Regen Braking and I was wondering if any of you had the same problem or if anyone would know exactly what the problem is.

So when you press the brake pedal lightly its not actually the brakes that kicks in but its the regen braking that starts the braking process. So far this happened to me twice, I'd press the brake lightly, the regen kicks in and the car starts slowing down. Then all of the sudden, it fell like the car starts moving forward fast again and I have to press the brake harder which results in a very unpleasant stop. It kind of fells like the regen braking stop working instantly for a fraction of a second.

Both time this happened, I was going down a hill and the weather was quite warm, not sure if that could be a factor with the issue I'm having. Also, I drive 100% of the time in B mode because I'm always in stop and go traffic and really enjoy one pedal driving.

So has anyone ever experienced similar issues while braking?

If your state of charge/battery % remaining is very high, you will not regenerate when you press the brake pedal or drive in B mode.

 

[Sparklebeard]

If it detects wheelslip it will cut regen, too.

Not sure what’s going on in your case. It wouldn’t hurt to contact the dealership, though unless it’s readily reproducible they might not do much about it. I don’t know of any firmware updates for the regen. My 2016 only ever had one for the battery charger control module.

How steep is the hill? If you can catch it happening on video that always helps, but that’s tricky when you’re the one driving and the issue isn’t readily reproducible!

 

[JoulesThief]

Try taking it out of "B" mode and driving in "D" mode using your foot brake 100%, and see if the problem goes away.

 

[uscpsycho]

If this was an ICE and you put the car in low gear on a steep hill your RPM could get too high and redline. I have no idea if there is anything comparable in an EV but perhaps your "RPM" are getting too high and the car is "upshifting" to prevent damage?

I don't know if you were in on the other thread, but do you realize that every time you come off the gas to coast in B your brake light comes on? Even if you are driving at speed. You are probably driving people behind you nuts in B all the time. I love driving in B but I significantly cut back my use of it because I think it's important to have good road manners.

 

[JoulesThief]

If this was an ICE and you put the car in low gear on a steep hill your RPM could get too high and redline. I have no idea if there is anything comparable in an EV but perhaps your "RPM" are getting too high and the car is "upshifting" to prevent damage?

I don't know if you were in on the other thread, but do you realize that every time you come off the gas to coast in B your brake light comes on? Even if you are driving at speed. You are probably driving people behind you nuts in B all the time. I love driving in B but I significantly cut back my use of it because I think it's important to have good road manners.

Psycho.... the e-Golf has a 1 speed transmission. Over revving the motor is impossible.

And, to quote you.... you don't know how he drives...



Overcharging the battery in regen mode, if battery is near full charge, might be possible, and cause loss of regenerative braking. Over revving the electric motor is impossible with a 1 speed transmission, the car is capable of 90 mph aprox. So is the motor and the transmission.

I've lost regenerative braking once, on a 100F hot day going down the Conejo grade on the 101 freeway, in CA, with gauge at about 5/8 showing. I think it's about 1200 feet or so lost at a 6 or 7% grade. I attribute it to the battery getting too hot from forced regenerative braking. I was in D3 at the time, holding 60 mph.

It's a VW "Safety Feature" with a passively cooled battery, instead of liquid cooled. One of it's cost /performance benefits to keep e-Golfs affordable, vs the extra cost and pricing of an actively cooled LiPo battery.

A VW "compliance" car is going to reach design limitations rather quickly, with the "Fast and Furious" style of driver.

 

[f1geek]

I have not had this happen and I've driven down a mountain on a hot day. I believe the Power gauge may provide useful information - I think when the battery gets hot or too low on SoC, the needle will move away from "Max" and into one of the other zones. You might want to glance at the power meter when this happens, if your pack SoC is above the red zone, because that may indicate a hot pack. Whether you use the brake pedal at less than the threshold force requested to switch to friction brakes or any mode with regen braking, the motor will slow the car by charging the battery. If you want to drive in B all the time, there is NOTHING wrong with that as long as you are able to module the accelerator pedal so as not to have heaving braking events when you don't want heavy braking events. If you brake hard either by pushing the brake pedal or by releasing the accelerator pedal to engage regen, the brake lights will come on as long as the deceleration rate is higher than the threshold value to turn on the brake lights. If this continues to happen, you should get it repaired at a VW dealer and also complain to VW corporate (get a case number).

 

[f1geek]

I just drove 236 miles today, including down 5000 feet. The battery pack was at 42.0 C when I got home (quick charged at ~40 kW from 15% SoC to 94% SoC after a 143 mile highway drive at an ambient temperature of about 93 F, to enable the 93 mile drive home). The car was flawless and I never saw the power gauge needle point to anything other than "Max". At no time did I have any loss of regenerative braking. The trip took 6 hours, including a 45 minute charge session.

 

[eGolfJoe]

I just drove 236 miles today, including down 5000 feet. The battery pack was at 42.0 C when I got home (quick charged at ~40 kW from 15% SoC to 94% SoC after a 143 mile highway drive at an ambient temperature of about 93 F, to enable the 93 mile drive home). The car was flawless and I never saw the power gauge needle point to anything other than "Max". At no time did I have any loss of regenerative braking. The trip took 6 hours, including a 45 minute charge session.

That's exceptional! Regarding the power gauge never moving off max, was this true even as the SoC was down to 15%? My power meter in freeway driving starts to drop at 41 miles remaining (with an average of 4.3 miles/KWh), and clearly in the 'normal' range when it hits around 31 miles remaining.

 

[f1geek]

Even at 15%, the power needle was still pointing to Max. I got the warning at 31 miles but performance did not change, even on the highway at 62 mph. Maybe you live in a very hot climate or are driving really fast with all A/C on full blast? I was driving as gently as I could in Eco mode the entire trip with the A/C set at 77 F (wearing shorts and a t-shirt, it was quite comfortable).

 

[eGolfJoe]

Even at 15%, the power needle was still pointing to Max. I got the warning at 31 miles but performance did not change, even on the highway at 62 mph. Maybe you live in a very hot climate or are driving really fast with all A/C on full blast? I was driving as gently as I could in Eco mode the entire trip with the A/C set at 77 F (wearing shorts and a t-shirt, it was quite comfortable).

Nope, this was 6:30am in the morning on the way to work. Cool morning ( 63 deg F) with an overcast marine layer, no ac or even heat running. Driving was on the freeway at 70 most of the way but the last mile is on surface streets. This happens each time the battery gets down to the last 40 miles

 

[nagaden]

Regen works very well the faster you’re going, but it’s worthless at low speeds and cannot stop the vehicle.

Using B mode at low speeds will slow my car almost to a stop, which works great in slow traffic. So, I think you are over exaggerating when you say “worthless” because it’s not.