B settings in icy conditions

[TonyL]

Hi,

Does anyone know if ABS etc. is active when using the B setting to regen.?

The recent icy conditions have left me wondering if thing could suddenly lock up!

thanks for any responses.

 

[jaapv]

If the wheel stops turning there is no regen...

 

[orkneydave]

I expect that regen will be similar to using an exhaust brake on a truck or engine braking in a car so will be better at slowing on ice and will not involve abs (which in my experience in the past is horrible on ice!).

Ive still got a week until I pick up mine so am purely guessing about the regen.

 

[Regulo]

I'm not sure about recent implementations of ABS, but previous systems were pretty lethal to anyone expecting them to slow you on sheet ice. If all four wheels stopped rotating, as far as the ABS was concerned you'd come to a halt! Result - sliding along with all four wheels locked, at a high rate of knots, wondering why the ABS wasn't helping you! Wonder if modern cars could use GPS to decide if you were still moving?

 

[jaapv]

ABS works best if one side of the car is on ice and the other on a grippy surface, it will stop it from spinning out of control. According to insurance statistics, cars without ABS have fewer crashes on slippery roads.

 

[TonyL]

Many thanks for the replies everyone and perhaps jaapv has answered my question.

The question arose from my experience of driving a Freelander with Hill Decent Control (which is linked to the ABS) engaged in the snow. Because there was no grip, the ABS would release the brakes to ensure wheels were not locked, which allowed you to steer the vehicle. If the B settings are not linked to the ABS, I can see a situation where grip is lost, wheels locked and the driver being a passenger until grip is available again because regen is trying to come back in. If B settings are linked to the ABS system, I would imagine it would "drop out" until sufficient grip was available.

What do you think?

For info., I do still have the Freelander and will use it when the weather is severe. I would rather throw my 08 Freelander in the ditch in the Peak district than my MY16 4HS!

 

[Bladevane]

From my own observations I would suggest the degree of regenerative braking is proportional to speed and the vehicle therefore never reaches zero speed. In other words as the vehicle slows the regenerative effect reduces. Therefore I assume the wheels will never lock up unless the brake pedal is pressed, at which point ABS becomes a factor.

 

[anko]

From my own observations I would suggest the degree of regenerative braking is proportional to speed and the vehicle therefore never reaches zero speed. In other words as the vehicle slows the regenerative effect reduces. Therefore I assume the wheels will never lock up unless the brake pedal is pressed, at which point ABS becomes a factor.

I think braking torque is constant (although reduced at higher speed in order not to dump to much power into the battery), and with constant torque, regen power reduces as speed reduces. But normally, a car would eventually come to a complete stop even with very little braking torque. No, they programmed the car to keep rolling at very little speed, to mimic to "auto gear box" experience. As a matter of fact, at that low speed the motors will take power from the battery to keep the car moving. Even in B5.

 

[Dusz]

Back to school physics. The output of a generator is proportional to the rate of charge of the magnetic field. So, there is a higher output at faster speeds (modified by the electronics when you select the different B settings) and will reduce the slower you become.

 

[Harald]

Back to school physics...

Back to the original question, translated in other words:

In situations when regenerative braking has a higher braking torque than the grip on an icy surface can withstand:
Will the torque be reduced automatically similar to the ABS system or will the wheel(s) start to slip or what else will happen?

Defining the same question from the other side:
When regeneration level is set to a certain value, let's assume B5: What will the Outlander do, when grip on slippery surface is insufficient for turning the wheel as needed for B5 regeneration rate? Will the regen torque be reduced?

The time of the year is nice for testing this behaviour in a location where it can be done safely. Maybe somebody can do this when finding icy conditions on a large free parking place or similar?

Best regards, Harald

 

[Regulo]

the slower you become.

I find as the years go on, I'm becoming proportionately slower!

 

[anko]

Back to school physics. The output of a generator is proportional to the rate of charge of the magnetic field. So, there is a higher output at faster speeds (modified by the electronics when you select the different B settings) and will reduce the slower you become.

How is that different from what I said? Or was it not meant to be different?

 

[jaapv]

Back to school physics...

Back to the original question, translated in other words:

In situations when regenerative braking has a higher braking torque than the grip on an icy surface can withstand:
Will the torque be reduced automatically similar to the ABS system or will the wheel(s) start to slip or what else will happen?

Defining the same question from the other side:
When regeneration level is set to a certain value, let's assume B5: What will the Outlander do, when grip on slippery surface is insufficient for turning the wheel as needed for B5 regeneration rate? Will the regen torque be reduced?

The time of the year is nice for testing this behaviour in a location where it can be done safely. Maybe somebody can do this when finding icy conditions on a large free parking place or similar?

Best regards, Harald

I would say that if a wheel loses grip during regen braking it will come to a stop, or at least lose rotational speed significantly. That in itself would reduce braking torque, creating a kind of autonomous ABS effect. (Disclaimer: this is a "stands-to-reason" theory which may well be disproved in a coming post )

 

[Harald]

I would say that if a wheel loses grip during regen braking it will come to a stop, or at least lose rotational speed significantly. That in itself would reduce braking torque, creating a kind of autonomous ABS effect. (Disclaimer: this is a "stands-to-reason" theory which may well be disproved in a coming post )

Yes, I agree. Let's see if somebody can proove it this winter.

Assuming a large parking place with black ice or similar:
Full loss of steering capability could be found out easily by simply shifting to B5.
Slip on rear wheel(s) only might be more difficult to identify. It's easy to take a video with the mobile phone but it might not have enough pictures per second for showing such dynamic behaviour.

 

[greendwarf]

Is it me or has Harald misunderstood what is happening with the regen "braking" effect. I thought it was just a reverse energy transfer rather than actual braking. Using B turns the electric motors into generators with the kinetic energy of the moving car converted into electricity for charging the battery. Entropy means that as this happens the kinetic energy (which is a combination of the mass of the car and the speed it is travelling at) reduces and, because the mass of the car stays constant, this reduction can only come by less speed - i.e. the "braking" effect. :idea:

 

[Harald]

Is it me or has Harald ...

Not sure what you mean ... and suggest to keep things simple.
The energy for regeneration comes of course from slowing down the car. (What else?)

The question in this thread is what happens when slippery conditions do not allow to transfer sufficient torque via the wheeels for a certain regeneration level. How will the car behave in this case?

 

[ps44]

This is a nice question....a bit the aeroplane on a treadmill :lol:

 

[Lance]

I think greendwarf is saying is that the braking force felt is the result of energy being transferred from the wheels to the motor rather than the other way round of the wheels being slowed as a result of a force being applied to them.

 

[greendwarf]

OK, I'll have another go.

As the Regen is only a function of the wheels turning and reducing the kinetic energy of a moving car rather than the application of external force in actual braking the question is irrelevant. There is no physical connection between the motors and the wheels, in the same way as a normal transmission, so no actual braking takes place and therefore the ABS is not involved.

However, in a real situation it is very likely the driver is also applying the brakes so ABS then becomes involved.

The advantage of Regen is that it is additionally reducing the speed of the car but that as the car slows so the "assistance" from Regen reduces and drops to zero long before the wheels stop (You can check this by putting car in B5 when stationary - it will move forward!) Because Regen on its own is self limiting in this way, I can't see how it can lock the wheels on its own and produce a skid but, of course, the car can have already lost grip without Regen or brakes playing a part. In these circumstances the wheels are probably already turning to slowly for Regen to be involved.

 

[anko]

As the Regen is only a function of the wheels turning and reducing the kinetic energy of a moving car rather than the application of external force in actual braking the question is irrelevant. There is no physical connection between the motors and the wheels, in the same way as a normal transmission, so no actual braking takes place and therefore the ABS is not involved..

Please no?

There are so many ways to approach this. Let me try two of them:

First there are several forces that can actively slow down wheels. Friction force from brake pads is one of them. Magnetic force from E-motors (or in this case generators) is another one. How would the tarmac, rubber and/or sheet of ice on the road know whether the wheel is slowed down by friction induced by a disc brake or by magnetic force induced by a generator? They don't, so they will react exactly the same.

Regen means feeding power back into the battery. This power fed into the battery comes from the wheels (to a certain extend, the e-motors or generators only play a role in converting mechanical energy into electric energy).It is calculated as Torque * RMP / 5252. In other words, Torque is calculated as Power * 5252 / RPM. So, imagine you are recovering energy at the rate of 20 kW while driving 40 km/h. At this speed the wheels are spinning at 301 RPM. So, combined torque at the axles must be 349 Nm. For ease of argument, lets say this torque is divided equally over all four wheels. Then the torque per wheel results in a force between wheel and tarmac of (349/4)/0.32 (radius of the wheel) = 272 N per wheel. You wanna bet this can make a wheel slip?

Don't forget, the wheel does not have to come to a stop to be skidding. Skidding means the wheel goes faster or slower than would be expected based on car speed.

BTW: Applying a certain amount of force per wheel will give a fixed positive or negative acceleration regardless of your actual speed. But the amount of power involved, does depend on speed. So, when we see the power needle returning from the 6 o'clock position to the 9 o'clock positing when we are loosing speed, it tells us stopping power is reduced. But it does not tell us stopping force is reduced.

(ignoring the fact that at higher speeds various forms of friction (wind, road, ...) eat up more power, resulting in less acceleration or more deceleration at higher speeds)