Limited slip differentials vs electronic control of brakes?

[g-force_addict]

Which is better?

I understand traction control is banned so teams must resort to limited slip diffs.
Even so the driver adjusts the locking as not to interfere with smooth cornering.

On the other hand E-diffs overheat and wear the brakes.
Maybe if allowed they could use two sets of disc brakes, maybe one inboard Jaguar independent rear suspension style to handle the e-diff and other set outboard to brake the car?

[spacer]

A proper differential distributes the available energy in such a way to (try and) maximise it's efficient usage.
Braking is turning part of this energy into useless heat. Not what we want.

[Jersey Tom]

On the other hand E-diffs overheat and wear the brakes.

An e-diff is a differential, not a brake system. E-diff's are limited slip differentials, just controlled electronically (hence the 'E') rather than mechanically (like with ramps in a Salisbury diff).

[riff_raff]

An electronic differential could only affect the relative rate of rotation between the rear wheels of an F1 car.

Of course, on many production cars, the ABS system is used quite effectively for stability control. By selectively applying the brakes at each corner, the vehicle can be actively steered independent of driver inputs at the steering wheel.

[JoaoB]

By the way, when a F1 E-diff acts to reduce the relative speed of the rear wheels, what is the mechanical way of working? Friction between surfaces? Electromagnetic fields? Fluid viscosity?

Is it allowed in F1 to have active diffs that actually force the outside wheel to rotate faster then the inside wheel, creating a proper torque vectoring effect?

[Jersey Tom]

I could be mistaken, but I believe that E-diffs have sets of clutch plates, like a Salisbury (ramp & clutch) would. The pressure on each set is somehow electronically controlled, but I'm not sure what actually puts the pressure on the plates.

That being the case you should be able to control how much pressure goes to the left- and right-side plates and do the "torque vectoring" stuff. I would think that'd be quite challenging to get the control strategy just the way you want it. Hell of a lot easier and probably just as effective to keep it equal L/R and adjust the overall gain from the steering wheel.

[autogyro]

The FIA control the technology used in F1 differentials.
AFAIK they are all electronicaly controlled mechanicaly operated torque vectoring designs.
They must not vector torque to achieve traction limiting from the complete axle.
This (as is the case in most powertrain regulations) eliminates all other types other than the FIA's choice.
Because of the limitations forced by regulation, the way the current diffs work adds to the problems achieving balanced braking, energy recovery and controlled rear tyre wear.

[JoaoB]

The FIA control the technology used in F1 differentials.
AFAIK they are all electronicaly controlled mechanicaly operated torque vectoring designs.
They must not vector torque to achieve traction limiting from the complete axle.
This (as is the case in most powertrain regulations) eliminates all other types other than the FIA's choice.
Because of the limitations forced by regulation, the way the current diffs work adds to the problems achieving balanced braking, energy recovery and controlled rear tyre wear.

If I understood right, torque vectoring is free as long as it is not removing power from the rear wheels like a TC would do... right?

[JoaoB]

I could be mistaken, but I believe that E-diffs have sets of clutch plates, like a Salisbury (ramp & clutch) would. The pressure on each set is somehow electronically controlled, but I'm not sure what actually puts the pressure on the plates.

That being the case you should be able to control how much pressure goes to the left- and right-side plates and do the "torque vectoring" stuff. I would think that'd be quite challenging to get the control strategy just the way you want it. Hell of a lot easier and probably just as effective to keep it equal L/R and adjust the overall gain from the steering wheel.

Thanks Jersey Tom. I would be surprised if teams would not try to get advantage of E-diff mapping to full extend regardless of the complication. At Monaco the diff must be extremely important to get brake and turn in stability without undesired understeer. Am I wrong?

[Tim.Wright]

There is a half decent discussion around here about the diffs. I'Ve been meaning to update ever since I got hold of my Ferrari F2000 book from Peter Wright. There is a cutaway section drawing of the diff there. Granted its quite old now but the design looked to be an hydraulicly actuated limited slip diff. No ramps, only an epicyclical gear train to do the initial torque split (which based on my dogy calcs on a 10 hour flight do not even split the torque 50:50 left right) and then the locking is controlled by the hydraulic piston acting on the clutch pack.

I'm pretty sure its not torque vectoring because torque vectoring diffs have a step-up stage of speed and this was missing in the drawing.

As to what they have now, I'd love to know. This clause about using it traction control doesn't rule out torque vectoring in my eyes but I've not put much thought into it to be honest.

[autogyro]

IMO a torque vectoring diff with some form of control is essential to being able to achieve reliable energy harvesting and to balance braking under deceleration and corner entry.
Torque vectoring also allows some control over under/oversteer through corners.
The limits of use would be the level of rear tyre wear.

An hydraulic CV Diff with toque vectoring would be the ideal but it would almost certainly be against the regulations because of the difficulty negating its inherent traction control properties.

[Jersey Tom]

I think you could do torque vectoring just with left- and right-side clutch engagement. Effectively lock (or partially lock) one half shaft to the input, force the load path. Hell, a Detroit Locker does "torque vectoring" by locking one or both output shafts while letting the other ratchet.

In any event, you don't need left/right torque vectoring to control under/over-steer balance on entry and exit. Can do it plenty with equal L/R clutch engagement. Hence my point of... why add the extra complexity? I mean, maybe it's a gain, maybe not.

[thisisatest]

i thought the diff had to mimic a mechanical limited slip, and the electronics function was to offer different settings of what a typical ramped friction plate diff could be adjusted to.

[Tommy Cookers]

agreed !

generally some open/nearly open diff' setting on corner entry
and locked/ nearly locked for exit

[autogyro]

Torque vectoring can still be mechanical with electronic control over apply clutches.
Vectoring allows a far better distribution of toque between each rear tyre.
It does have a direct effect on over/under steer both in corner entry under braking/harvesting and exit under power.
It is also the best method using a mechanical system for traction limiting without actualy being TC.