Regeneration brake lights

[SDP79]

Bit of a safety fail this. When slowing down with KERS and adaptive cruise do the brakes operate as well? If they do then the brake lights should operate to warn other drivers. Decrease in speed can be quite dramatic at times so not brake light activation is a bit of a worry!

 

[defeatedbythecat]

I believe that if the breaks are applied as part of AAC then the lights do come on. But that's only from what I seem to recall reading elsewhere.

 

[johnd973]

Bit of a safety fail this. When slowing down with KERS and adaptive cruise do the brakes operate as well? If they do then the brake lights should operate to warn other drivers. Decrease in speed can be quite dramatic at times so not brake light activation is a bit of a worry!

I believe that any time the friction brakes operate, the brake lights illuminate regardless of whether they are operated by the foot pedal or autonomously

 

[Ozzie1989]

Exactly, everyone speaks of these drivers who abide by basic road sense e.g. keeping a safe distance from the car in front. Where do you find them these days? ?

Their fault or not, I'd rather they didn't run into the back of me when the kids are on board or a dog in the back.

Personally even in my ICE vehicles when slowing using engine braking I was always taught to cover the brake pedal and lightly press it to warn drivers behind if required (e.g. roadcraft teaches you to always be aware of what's going on behind as well as in front and to the sides). I'd continue to do this but not everyone does, so it makes sense that if the vehicle is slowing over a certain rate the brake lights come on.

For those who say the vehicle wouldn't have been released without thorough testing I completely agree, however the statement below from MG isn't very confidence inspiring!

"After looking into this, we can confirm the MG5 EV would require this feature to be fully functioning in order to pass regulations.... "

 

[johnd973]

I would guess the reason the 5 and ZS are not true one pedal cars is because the regen has been intentionally been kept at a level below that where brake light activation is required for certification. It's quite complex to calculate when you show the brake light (think of the complexities around steep hills and high speed traffic) and therefore a lot easier to make sure you never have to show it under regeneration.

Ultimately this is a car which is for sale, having passed certification in a large number of countries. Given how aligned global vehicle type approvals are I really cannot imagine a scenario where a vehicle with a compliance issue would pass type approval in multiple countries.

 

[Fluffykins]

There’s a much higher amount of deceleration caused by regen KERS compared to engine braking on an ICE car.

Not if you drop an ICE car a cog or two for a corner.

 

[JimB]

I cannot imagine the 5 or ZS would be on sale in the UK if they did not meet construction and use regulations. Type approval is carried out by the vehicle certification agency on production samples of vehicles before they can be sold in the UK and is quite a rigorous process.

I believe there are other EV's which also do not illuminate their brake lights under regen (Renault Zoe, Kangoo and first generation Nissan Leaf), it's not an exclusive trait of the MG's.

If someone runs into the back of you under regen then they were not maintaining a safe stopping distance in accordance with the highway code and were possibly driving with undue care and attention. I don't think the regen is strong enough that it should take anybody driving sensibly by surprise! It's no different than driving an ICE car and changing down from say 4th gear to 2nd to slow down!

The ice engine braking example is a good point well made.

My Outlander phev is 6 years old and therefore maybe not built to current regulations, but brake lights only illuminate using level 5 regen (highest level) and then only if over (I think) 30 mph.

Otherwise, as said, the constant illuminations would be inconsistent with the pattern exhibited by ice cars on the overrun or engine braking.

 

[JimB]

There's another complication that ice cars don't have....irrespective of your speed and kers setting, if your battery is fully charged the car is hardly going to slow down at all when you take your foot off the accelerator, because, as you know, you can't regen into a full battery.

Great if the software can factor in the battery state to decide whether to light the fires on the rear end.

 

[johnd973]

There's another complication that ice cars don't have....irrespective of your speed and kers setting, if your battery is fully charged the car is hardly going to slow down at all when you take your foot off the accelerator, because, as you know, you can't regen into a full battery.

Great if the software can factor in the battery state to decide whether to light the fires on the rear end.

Yep, there are a lot of complicated technical issues to address and an unimaginable number of scenarios to consider when designing the software. If you are cost sensitive and aiming your products at a particular market segment then it's much cheaper and easier to bypass the problem by making sure the regen is never strong enough to require the brake lights to come on. I suspect this is the approach Saic have taken.

 

[Alb]

I'd consider it quite a simple problem technically.
The motor controller constantly monitors torque so the lamp drive just needs to be triggered when it exceeds a preset negative value.

 

[JimB]

I'd consider it quite a simple problem technically.
The motor controller constantly monitors torque so the lamp drive just needs to be triggered when it exceeds a preset negative value.

When you think that even most mobile phones have a 10 cent accelerometer in them maybe there's another possible cheap solution.

 

[johnd973]

I'd consider it quite a simple problem technically.
The motor controller constantly monitors torque so the lamp drive just needs to be triggered when it exceeds a preset negative value.

Now throw in a steep hill, up or down and imagine the effect that has on your measurement at different throttle positions and in different road conditions! Now load the car with as much luggage as you can and add a roof box! What is your torque measurement doing now? Now add some ice, bald tyres and put Lewis Hamilton behind the wheel! Now just for fun chuck in a 30mph head or tail wind!

Too many scenarios, much easier to avoid the problem!

Have a fair amount of experience in software engineering in the automotive industry and there is no such thing as a simple problem.

 

[evmick]

So, there is indeed a statement in the Type approval regs (not sure if these have been superseded) stating

Electric regenerative braking systems as defined in paragraph 2.17. of this Regulation, which produce a retarding force upon release of the accelerator control, shall generate the signal mentioned above according to the following provisions:

Vehicle decelerations
Signal generation ≤ 0.7 m/s² The signal shall not be generated

0.7 m/s² and ≤ 1.3 m/s² The signal may be generated
1.3 m/s² The signal shall be generated

In all cases the signal shall be de-activated at the latest when the deceleration has fallen below 0.7 m/s².

See https://unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/2018/R013hr4e.pdf, section 5.2.22.4

Not saying I am massively worried about it, like others I generally tap the brake pedal anyway if I want to make sure whoever is behind knows I'm slowing down quickly (I tend to drive in KERS 3 all the time). But it does feel like a software update will have to be issued by MG at some point.

 

[smokie]

When I had my test drive the saleslady told me how to put it in KERS3 which felt less aggressive in its braking than my Ampera, which also doesn't show lights.

 

[Prof1967]

With everything said on this topic has anyone actually been back ended while using KERS as yet?

 

[Justin H]

With everything said on this topic has anyone actually been back ended while using KERS as yet?

Not yet but people do get worryingly close. I have done over 4000 miles now on motorways and A/B roads. I think that at a certain level of breaking force in kers 3 the break lights should come on. Experience shows that other road users do struggle when they are driving behind me regardless of how slowly I reduce speed with the regenerative braking.

 

[smokie]

Someone detailed the scientific measurement of when the brake lights should be lit up further up this thread. Either Kers3 reaches or it doesn't reach the standard, hopefully someone has thought to test it. I imagine there is a similar standard in all countries.

Maybe those who feel strongly ought to ask the relevant body whether the standard is still appropriate, and ask MG whether the car meets the standard.

 

[Justin H]

Someone detailed the scientific measurement of when the brake lights should be lit up further up this thread. Either Kers3 reaches or it doesn't reach the standard, hopefully someone has thought to test it. I imagine there is a similar standard in all countries.

Maybe those who feel strongly ought to ask the relevant body whether the standard is still appropriate, and ask MG whether the car meets the standard.

If you look further up the thread Kompins seems to have done just that. He has an interesting response from MG.

 

[smokie]

Oh, yeah, forgot that, thanks! Good that MG UK have accepted and escalated the potential for an issue.

 

[Kompins]

I chased up my contact at MG last week and have had a positive response, basically they have test vehicles set up in the UK and China and "We are nearing completion of the testing, and will let you know the outcome within the next 2 weeks."