B settings in icy conditions

[greendwarf]

Er, all very clever, anko, but rather incomprehensible (to me :lol and nothing really to do with the ABS which stops the wheels locking so as to offer assistance in a skid. My point is that the question about Regen & ABS is irrelevant as there is no interplay between them and by the time ABS gets involved Regen has long ceased to function - do you agree?

 

[anko]

I do agree. My response was triggered by the "no actual braking occurs". Not by the ABS remark. Should have left that out when quoting you

 

[greendwarf]

Ah, yes I see. Of course, I meant no application of an external mechanical force to the wheels by the car to effect braking, when the energy conversion is into heat through friction. My understanding is that the use of the motors in reverse is to "suck" away the excess kinetic energy, which does produce a negative torque and slows the car - but then I failed A-level physics 50 years ago, so prefer to think in layman's terms.

 

[TonyL]

Thanks all for your contributions.

There is some really interesting discussion here but i am not sure we have established whether the scenario I presented is a real possibility.

For those that make the point that if the wheel isn't turning there is no regen., it does seem that traction and steering could still be lost under regen. with dramatic consequences.

For others who comment on the fact that regen. is not like traditional braking and, therefore, would not be linked to ABS, seem to be missing the point that ABS actually restricts the braking to allow the wheel to turn and provide traction/grip. This is why it is less useful in snow, as you find yourself with a car not stopping and a solid brake pedal!

The above happens because ABS is monitoring the individual wheel speeds and my question was really, is ABS linked to the regen. function. That is, is something monitoring the wheel speeds when regen. is active and would it be reduced stopped if traction is lost?

Thanks again.

 

[anko]

The above happens because ABS is monitoring the individual wheel speeds and my question was really, is ABS linked to the regen. function. That is, is something monitoring the wheel speeds when regen. is active and would it be reduced stopped if traction is lost?

If there was, it would have to be on a per-axle basis and not on a per-wheel basis, as regen is controllable per motor, hence axle, and not per wheel.

From what the Dutch distributer told me, regen was designed to provide a specific deceleration (for example B5 should result in 0.11 G or 1 m/s2 in B5). Regen power should be adopted to result in that specific acceleration. They said that when towing or heavily loaded, regen power should increase in order to result in the the same amount of deceleration (whether that is true?). But this would also mean that regen power could be increased when the car was not slowing down as fast as planned for ... because of wheel spin.

I cannot imagine they would be that stupid ....

 

[Steepndeep]

Sorry for being late into this discussion but I thought I add my 2 cents.

First, ABS and E-regen (Electricity regeneration using B settings) are to my knowledge 2 totally separate systems. Have nothing to do with eachother. This is my assumption but I may be wrong (I do not think so though).

On ABS as there seams to be some misconceptions whether it is good in snow or not. In scandinavian countries since ABS has been introduced crashes in snow has dropped considerably. ABS is the best thing that has happened and there is almost no condition when it is not better than a very, very good driver. All ABS systems work roughly the same. Above a certain low speed (5-10 km/h) they work and below that they are switched off. When they work they quickly break each wheel until the wheel stops turning and then they release and start all over, this within 0.5 seconds or less ( the better system the shorter time). So effectively each wheel skids for a short time and then start breaking again. When breaking with ABS you should always break with maximum force (to enable ABS) and will feel the vibrations in the breakpedal from the ABS system.

B regen is just feeding power back to batteries and B5 is a fairly strong power feedback. I guess if it was black-ice (extremely slippery, so slippery that you almost cannot stand on 2 feets on a level surface) and you applied B5 all wheels would stop imediately and the car would start skidding. Of course the regen would then stop and the wheels be released but that would be TOO LATE. You would be heading for the ditch already and having a hard time recovering.

E.g. I was driving a Skoda Fabia Diesel some years ago on black-ice and realised too late that I was on black-ice. Took my right foot of the gaspedal in 5´th gear and both front wheels immediately skidded. Fortunately straight road so freewheeling fixed it but it was so slippery that it was impossible to increase speed without going into the ditch. Note that in Sweden all roads are slightly convex to get rainwater off the surface but that was enough to make it impossible to accelerate. And that was with top of the line winter tyres.

# Ankos latest post
Just saw it when I was uploading and decided to comment. I do not think the Dutch distributor is right. I have been towing a heavy load and did not notice a higher B5 regen, only same regen power and thus longer "stopping distance".

 

[anko]

B regen is just feeding power back to batteries and B5 is a fairly strong power feedback. I guess if it was black-ice (extremely slippery, so slippery that you almost cannot stand on 2 feets on a level surface) and you applied B5 all wheels would stop imediately and the car would start skidding. Of course the regen would then stop and the wheels be released but that would be TOO LATE.

Why would you think that releasing the wheels in case of of a regen induced skid would take any longer than it would with ABS brakes? Electronics versus hydraulics + mechanics. Electronics should be much faster (if programmed properly), if you ask me.

 

[Steepndeep]

#anko
Well I did not think of it that way. But now when you say it I do not agree. It is not electronics vs hydraulics, it is sw brain with hydraulics actuation vs. sw brain with electrical actuation. And comparing hydraulic actuation (engineered to be fast in ABS system) vs electrical actuation (not engineered to be fast, just my assumption because it was not engineered for black ice but for regen) I assume the ABS wins. But I do not know, will test when suitable wheather arrives

 

[Harald]

But I do not know, will test when suitable wheather arrives

Thank you, that's great.

 

[anko]

#anko
Well I did not think of it that way. But now when you say it I do not agree. It is not electronics vs hydraulics, it is sw brain with hydraulics actuation vs. sw brain with electrical actuation. And comparing hydraulic actuation (engineered to be fast in ABS system) vs electrical actuation (not engineered to be fast, just my assumption because it was not engineered for black ice but for regen) I assume the ABS wins. But I do not know, will test when suitable wheather arrives

So, you don't agree with me because of something you assume? Interesting

Have you ever used the CC? Have you noticed how well the PHEV maintains its speed over varying conditions? This is done using the same SW brain plus electronic actuation. Fuel consumption and ICE output is constant. But power to the wheels is manipulated by making the generator generate more or less power. Very effective.

 

[StevieB]

Some good points made.

Firstly though, selecting B5 when already going quite slow makes little difference on mine. I'm pretty sure that it is speed sensitive. It is already battery capacity sensitive.

On to the point of ABS, technically, I'll stick my neck out and say that it will not kick in at all via the direct ABS route if traction is lost. What will make it kick in regardless of braking if the wheel does loose traction (spins less or more than others) will be the ESP (ASC on Mitsi). I know the system utilises ABS to make it work, but the process is a seperate module.

So if you're travelling, and B5 makes you lose traction on one of the wheels, ASC will kick in. The general process though, would only be similar to if you geared down in the snow, say went from 5th gear directly to 2nd on a mnaual car. This could make you lose traction, but again, ASC should kick in, but it will have little affect on snow. Note doing this on a Ferrari or a Lambo etc, and doing higher speeds can make the back end spin round on you!

Generally, I use B5 on snow rather than brake, as it is like an engine brake - similar to using Low gear on a 4x4 and not touching the brake itself. I've done a fair bit of off-road driving in the past and found this the best way. Other than that, drive like it like any other car in snow, taking it steady and leaving plenty of room between car in front.

 

[greendwarf]

This discussion is still being fuelled by a lack of knowledge. I have always understood ABS is linked to the hydraulic system to modify the pressure being applied by the driver through the pedal and so prevent wheels locking. It might be that the PHEV has some special arrangement to include the Regen into the control but, at present, we have no info only supposition.

However, on the increased Regen when towing or heavily laden question - surely this just schoolboy physics again. A larger mass at the same speed will have more kinetic energy available for conversion into electricity for the battery. Unless the car limits the amount generated to protect the battery, the braking torque will be similarly increased but the braking "effect" will remain the same.

Whilst I accept that car can lose traction (skid) without braking e.g. cornering when lateral forces break the adhesion, I doubt that the deceleration from Regen would, on its own, be sufficient, especially as it stops before the wheels do. But, has anybody ever managed to induce a skid under, similar engine braking circumstances without actually using the brakes?

 

[anko]

However, on the increased Regen when towing or heavily laden question - surely this just schoolboy physics again. A larger mass at the same speed will have more kinetic energy available for conversion into electricity for the battery. Unless the car limits the amount generated to protect the battery, the braking torque will be similarly increased but the braking "effect" will remain the same.

Indeed:

This discussion is still being fuelled by a lack of knowledge.

Braking force does not depend on mass, it depends on (negative) torque delivered by the E-motors.

The PHEV ECU sends messages to the E-motors via CANBUS (at a very high frequency) to request an amount of positive or negative torque (Believe me, I can see these messages. And also the messages the E-motors use to report back how much torque was actually delivered). Depending on mass, incline and other factors this torque (when delivered) results in a specific amount acceleration or deceleration. This amount of acceleration or deceleration is independant of speed.

The question that rises is: is the amount of negative torque requested from the motors during regen fixed (providing a given B-setting) or is it, for example when towing, adjusted by the PHEV ECU in order to establish the same predefined amount of deceleration? If it is fixed, it will result in less deceleration. If it is adjusted, it will result in higher regen torque (and thus power).

Bottom line: without intervention by the ECU adding mass will not result in higher regen power. Same as while accelerating: Adding mass does not increase power. It reduces acceleration. Unless you press harder on the GO pedal.

(all of the above ignoring any braking that might be going on on the trailer itself).

Whilst I accept that car can lose traction (skid) without braking e.g. cornering when lateral forces break the adhesion, I doubt that the deceleration from Regen would, on its own, be sufficient, especially as it stops before the wheels do.

Again, wheels do not have to be stopped to loose grip. The amount of grip you have allows for a specific amount of force to be transferred from the wheels to the road (acceleration) or vice versa (deceleration). When (positive or negative) torque from e-motors result in more force at the contact surface than grip can handle it will result in skidding. Even when the wheels are still turning.

BTW: not always is it the lateral forces themselves that make a car loose grip in corners. It is often the combination of lateral forces + forces associated with either propelling or braking the car. Together these forces form a force vector. When the size of this vector exceeds what grip can deal with, you will start skidding. You can be going around a corner very nicely and drift to the outside of the corner when you hit the go or stop pedal.

 

[TonyL]

OK everyone one. I have returned today from 40 degrres in Botswana to find the perfect conditions to test my concerns.

Crossing the Peak District with a good amounts of snow still on the road, I found it easy to lose traction with heavy acceleration or braking but could not get this to happen as a result of regen. (even on B5).

Admittedly, this was at speeds of no more than 20mph but my fears of an uncontrolled skid appear to be unlikely.

Thank you all for your contributions.

 

[anko]

On the Dutch Ampera E forum one person said that L-mode (comparable to B5) allowed them to drift (I think 'drift' is not really what he meant considering the Ampera E is FWD, but still). Another person said that on a very slippery stretch of road, he disengaged L-mode to keep more control while slowing down.

Both responses suggests that the Ampera E does allow regenerative braking to cause skidding.

 

[vlado61]

This morning I drove 40 miles on the icy roads on D5 and 4WD lock. It was perfectly ok.
Maximum speed 50 mph. The battery was full and lasted for 15 miles. The heater was blowing 25C all the time with the seat heating on - average consumption 5.5 L/100km (51.36 miles per gallon)! EV 51%!

 

[jaapv]

On the Dutch Ampera E forum one person said that L-mode (comparable to B5) allowed them to drift (I think 'drift' is not really what he meant considering the Ampera E is FWD, but still). Another person said that on a very slippery stretch of road, he disengaged L-mode to keep more control while slowing down.

Both responses suggests that the Ampera E does allow regenerative braking to cause skidding.

Oh, you can drift an FWD all right, just play around with the handbrake
It is just the other way around from an RWD, instead of breaking adhesion by feeding the rear wheels power, you do so by braking them.

 

[anko]

Oh, you can drift an FWD all right, just play around with the handbrake

Of course you can. But by means of (regenerative) braking the front wheels?

 

[jaapv]

A front-wheel drift? Might make things interesting... :lol:

 

[anko]

As interesting. But not nearly as impressive :mrgreen: