KERS3 and ice

[MonsterMonster]

I was wondering how does the KERS3 mode perform when slowing down on icey or slippery roads. Is it safer than using brakes?

 

[busa]

Aren't brakes for braking?

 

[Jomarkh]

I was wondering how does the KERS3 mode perform when slowing down on icey or slippery roads. Is it safer than using brakes?

I had the same thought the other day.
I mainly switch into eco and kers3 and have not had any issues with this.
I probably dont get so much snow down south but did wonder about wet leafy roads.

 

[Cocijo]

This is an interesting topic that spans all EV’s really.
As far as I know there is no abs active under kers so if grip is lost the car will skid - but I’ve never actually had this happen, so I can’t confirm this from my experiences. The first part of applying the friction brakes (I think) applies some kers initially then the friction brakes take over if more brake pedal pressure is applied (again this may vary depending on the set up/model).
There has been much debate about using regeneration in slippery conditions. The general consensus appears to be to set it to a low (or turn it off if available) regen level if very slippery.

 

[Ozzie1989]

One thing to remember is that KERS operates on the front wheels only so any significant KERS braking with the front wheels on ice could result in loss of grip and skidding.

However from past experience on ice it is sometimes the application of the brakes on the rear that causes the vehicle to skew rather than remaining straight which can alter the outcome of the skid.

As with any loss of grip situation the main enemy is momentum so keeping it slow and making your actions smooth is key, hence KERS may help as you can feather the throttle and use it to your advantage without lifting your foot between pedals or accidentally stabbing the brake causing a skid.

 

[Kithmo]

This is an interesting topic that spans all EV’s really.
As far as I know there is no abs active under kers so if grip is lost the car will skid - but I’ve never actually had this happen, so I can’t confirm this from my experiences. The first part of applying the friction brakes (I think) applies some kers initially then the friction brakes take over if more brake pedal pressure is applied (again this may vary depending on the set up/model).
There has been much debate about using regeneration in slippery conditions. The general consensus appears to be to set it to a low (or turn it off if available) regen level if very slippery.

Had this a few times with the Prius, it gives the impression that the car is suddenly accelerating, not noticed it yet with the ZS though.
KERS is automatically decreased when the battery is cold anyway, as the battery can't take as much charge.

 

[Alb]

You really need to experiment.
Transitions in speed need to be smooth so you may find in some circumstances that KERS3 is too much.

 

[busa]

What about ABS? does that operate with KERS? brakes are for braking

 

[Cocijo]

KERS is a form of brake

 

[busa]

so KERS operates the ABS, traction control??

 

[Cocijo]

You tell me, but it‘s still a form of brake.

 

[busa]

NO it doesn't operate the ABS or Traction control

 

[Cocijo]

It’s called regenerative braking

 

[busa]

OMG, I really didn't know that!! ever day is a school day......maybe I'll get a few eggs and suck on those, so your happy to use KERS only in snow???ice, forget about the ABS, traction control, small little things like those safety devices????

 

[busa]

In fact I can't be assed with an argument over this so fill you boots, say what ever you want I'm out

 

[MonsterMonster]

In fact I can't be assed with an argument over this so fill you boots, say what ever you want I'm out

Good

 

[djenson]

Im talking about performance in Slowing down here not breaking to a full stop


Never used An MG in snow, but when we had that really bad lot of snow in the UK a few years ago we had a hybrid ford fusion on hire with a Low Range. SLowing down with the engine/motor breaking in the low gear felt much more stable and consistent and felt more in control compared to typically pedal breaking. I think is because where the low gear is just trying to get the wheel to slow down to a certain speed, the breaks are trying to stop the car completely. As Alb Says though, you would need to experiment in safe conditions to see what happens in the MG.

@busa I think you thinking that @MonsterMonster is trying to replace the normal breaks with KERS. That's not his goal from my understanding. Breaks should obviously be used when you need to stop quickly, But he is asking is it safe/stable to slow the car using the KERS system in slippery conditions, or is the car going to go sideways.

 

[MonsterMonster]

Thanks for the mostly helpful replies. KERS3 is pushed as a feature to slow the car when lifting off. I'll find out soon enough as there is a fast exiting fork junction off the A158 which is a muddy icey lane with an adverse camber. Braking here is always fraught.

 

[AnonymouseDriva]

NO it doesn't operate the ABS or Traction control

Interesting concept though - it doesn't operate ABS by pulsing brakes, but should prevent wheel lock in it's own way. (albeit not one I would be relying on in icy conditions!)

my logic (albeit guessing here - feel free to correct!) is that KERS is using the motion of the wheels to generate electricity. the 'braking' force is actually the resistance generated by this process.

the deduction therefore is that stopped wheels = no motion = no generation and therefore no resistive force, so the 'brake' has been 'released' preventing wheel lock.

Outside of my deductive musings though and back to documented functions, the manual says that energy cannot be regenerated or limited under some conditions, one of which is "During torque intervention (SCS or traction control operation) ". Whilst it refers to regeneration there, it doesn't specify whether braking continues via alternative means (although if you have ever run over a drain cover when slowing on KERS, you'll already know that it doesn't!)

It does imply though that traction control is in fact active and ready to intervene even when slowing on KERS, although the intervention seems to be to just stop regen and coast... hence (I suppose) the big warning at the top of that page:

Back to OP's question though, that of using KERS3 on icy or slippery modes.
I would say, probably best not to use it for three reasons:

• As @busa said, you don't have 'proper' ABS. It'll just stop slowing, meaning that after your reaction time to move to the brake, you'll then have to brake harder (which you don't want to do)
• KERS only applies braking force to the front wheels in this car. I'm no engineer, but it seems to me that you would want to guarantee maximum traction in icy conditions with the braking force distributed across all contact points with the road.
• Believe it or not (and to be fair, I only know now because I looked when replying to this thread) it literally says not to use KERS3 on slippery roads in the manual! P164 - "It is recommended to choose Light or Moderate levels on surfaces that have low adhesion levels (e.g. icy roads)."

Personally, I'm an Eco / 3 kinda guy, but I haven't driven this in ice or snow yet. I think I'll be looking at Eco / 1 for that when I do.

 

[biffo]

OMG, I really didn't know that!! ever day is a school day......maybe I'll get a few eggs and suck on those, so your happy to use KERS only in snow???ice, forget about the ABS, traction control, small little things like those safety devices????

I don't think the original question was a binary, either/or concept - at least not to me anyway. It felt more analogous to using engine braking in an ICE car vs the brakes - but not to the exclusion of them.

This is an interesting topic that spans all EV’s really.
As far as I know there is no abs active under kers so if grip is lost the car will skid - but I’ve never actually had this happen, so I can’t confirm this from my experiences. The first part of applying the friction brakes (I think) applies some kers initially then the friction brakes take over if more brake pedal pressure is applied (again this may vary depending on the set up/model).
There has been much debate about using regeneration in slippery conditions. The general consensus appears to be to set it to a low (or turn it off if available) regen level if very slippery.

I'd read the same somewhere, that higher levels of regen can cause locking up of a wheel in very icy conditions - the same as strong engine braking can. I suspect, since KERS seems to be quite variable in strength based on battery temperature, charge level, speed, etc - combined with tyre traction due to road conditions and tyre abilities - and variables on a model to model basis too - then either experimenting in a safe location, or setting to minimum, might be wise.

Personally, I'll stick with '2' (as I'm lazy and usually leave in 'N2') - and if I skid when KERS kicks in, I'll knock it back to '1'.