Driver-adjusted differential locking

[Tim.Wright]

Well you cant do that with a clutch & ramp style diff no matter how much gagetry you add to it.

[autogyro]

Its not realy a diff then is it.

[Steven]

Ok I spoke to XTrac, they provided Marussia (Virgin Racing) with a gearbox and differential in their debut year.

They confirmed me this: "The differential is an active hydraulic type controlled by a Moog valve which can operate at approximately 200bar pressure. The 50/50 left to right torque split is achieved using an epicyclic with an annulus, sun gear and planet gears."

[Tim.Wright]

Its not realy a diff then is it.

Well it allows the rear wheels to rotate at different speeds, so in my mind it fits the definition

[autogyro]

Its not realy a diff then is it.

Well it allows the rear wheels to rotate at different speeds, so in my mind it fits the definition

It would not be 'allowing' anything if it was actively applying torque under control.
It would be torque and traction control.
I have designed both a hydraulic method and an electronic.
It is not possible to control any type of conventional diff in this way.
Conventional diffs have a defined mechanical link between the two wheels.
Any control system used with them is passive and not active in its operation.

[autogyro]

Ok I spoke to XTrac, they provided Marussia (Virgin Racing) with a gearbox and differential in their debut year.

They confirmed me this: "The differential is an active hydraulic type controlled by a Moog valve which can operate at approximately 200bar pressure. The 50/50 left to right torque split is achieved using an epicyclic with an annulus, sun gear and planet gears."

The 'control system' in this diff is 'active' moog controlled hydraulic but its effect on the differential is passive.
The gear set in the diff still transfers the torque from one side to the other and forms the actual differential.
If it were an active hydraulic 'type' it would not use a planetary gear set.

[Tim.Wright]

So I think we can agree its a "normal" locking diff (albeit with a planetary gear set) with hydraulic control of the clutch locking?

[autogyro]

Yes Tim, but X Track describe it incorrectly.
It is definitely not an active hydraulic differential.

[autogyro]

It is also not a 'locking' diff Tim. it is a slipper diff with hydraulically controlled slipping.
The main problem is high wear rate if such diffs are used ambitiously.

[Tim.Wright]

I think we have a different definition of locking diff here. When I say locking diff I mean a diff which has ramps in the cage which operate a clutch pack. If this is what you call a slipper diff, then I agree with you.

With respect to the Xtrac description, I think its fair to call that a hydraulic diff. Its a diff that has hydraulics in it. Ok its not transferring the power to the wheels hydraulically but there are no diffs commonplace in either road or race cars which are, correct?

The only part I can't figure out (at least immediately) is how to achieve the initial 50/50% torque split with a planetary gearset. When I imagine a scheme of a single stage planetary gearset with the diff input applied to the planet gear carrier and the outputs being the sun ring gear, the torque split is not 50% because the planetary gear contact force is applied at different radii for the left and right wheels. what do you think?

[autogyro]

I agree Tim no single planetary gear diff can apply equal torque to both outputs.
That is why it is always one wheel that 'lights' up before the other on take off with an 'open' diff, all else being equal.
A ramped diff uses the ramps to control the rate of friction plate application, so a conventional ramped diff cannot use variable hydraulic apply to vary the limited slip action. Usualy they have a pre set plate torque contact figure, or no plates at all. I made a lot of trial modifictions to Jack Knight roller lock diffs to prevent sudden power on lock ups, also major development on the 'Salisbury' plated types, mainly to reduce wear when used hard in rally cars.
These are some of the basic difference between LSD and a locker diffs.

[Tim.Wright]

I'd like to continue this discusion until we arrive at a likely schematic for an F1 diff. Its pretty interesting.

A ramped diff uses the ramps to control the rate of friction plate application, so a conventional ramped diff cannot use variable hydraulic apply to vary the limited slip action.

This is not completely true, one possible arrangment is to have a hydraulic piston operating in parallel to the ramps. This way you get some locking even without the electronics helping, then the hydraulics apply an extra plate force on top of that.

One thing I'm having a hard time believing is that they have a torque bias from the planetary arrangement. They must use some other gearing to give a normal 50% torque split like an open diff.

Tim

[autogyro]

I dont deny that there are some clever guys out there Tim.
However, I agree with you.
If there is a conventional planetary diff between the wheels, then I cannot see how it is possible to control the amount of torque applied to each wheel.
The only use I can see for the X track design would be for controlling the locking or slipping of the diff outputs, to prevent a loss of traction to the side that shows a sudden increase in wheel rpm and a sudden reduction therefore of torque at that wheel.
This is conventional limited slip action and not torque vectoring however.
Maybe they use the plates to 'brake' the shaft on one side to reproduce Gordon Murrays brake steer system.
If they do it will annoy him no end as the ban on his system was part of the reason he left F1.
Controlled braking on one side would allow torque vectoring to the other side.
This would help control over/under steer and would be usefull under braking to balance KERS with rear tyre deg.
If I am right no wonder they are having gearbox problems using such a heath robinson cock up.
Aero forcing the issue again of course.

To control the amount of torque applied to each wheel 'sensibly' you need first to remove the planetary set.
An annulus driving two clutch drums connected through the plates to the drive shafts would be one way.
Excess plate wear would result in loss of drive though and how would you police traction control?
I had a better design using small hydraulic pumps one on each side rotating with the shafts.
With the flow through the pumps valved off the pumps locked and the amount each pump bled fluid controlled the slip action and vectored the torque
Again how do you police traction control?
Should be easier to police than with slipping plates though.
Maybe I should sell it? hahaha

[strad]

Picture a posi rear end with it's clutch pack, but with the ability to hydraulically apply those clutches when you want instead of when a wheel slips. Ever drive something with a nice new tight clutch pack, oh say on the freeway for a distance and when you get off and make a turn at the end of the off ramp you skip a bit around the corner because the clutches have swollen with heat and locked up like a spool? Think of being able to do that to varying degrees by applying pressure..Now you can have pressure on the inside wheel and MAKE the car want to turn in.

[Tim.Wright]

Auto I need some time to digest all of that.

Think of being able to do that to varying degrees by applying pressure..Now you can have pressure on the inside wheel and MAKE the car want to turn in.

I don't get exactly what you mean there. Applying pressure to lock the plate on the inside wheel will increase the torque being sent to it, and this will be trying to turn the car out of the corner.

With this type of diff, even with total control over the clutch force using hydraulics, you cannot bias the torque to the faster wheel (which is usually the outside wheel).

Tim