Driver-adjusted differential locking

[Steven]

We all know that drivers can change the amount of lock on the differential by switching a button on their steering wheel.

However, knowing that teams use limited slip differentials, can anyone explain what does actually happen mechanically when a driver changes this setting?

[Jersey Tom]

I don't know this for fact, but I would venture an educated guess as follows:

I would presume them to have similar functionality to a Salisbury type differential with varying amounts of thrust on clutch plates providing the "locking" or slip-limiting action. In a conventional "ramp and clutch" differential, there is some preload applied to the clutches which provides a some "locking" even when no driving or braking torque is applied. Then there are ramp angles which determine how much the clutches are forced against each other either when throttle or applied or engine braking torque goes through the system.

I would expect that a Formula 1 differential uses an electronic and/or hydraulic means to apply the varying amounts of force to the clutch plates. As is seen sometimes on F1 steering wheels, "Entry" diff control would presumably control the gain of clutch plate thrust while under engine braking (decel ramps in a standard Salisbury)... "Mid" would be associated neutral-throttle preload, and "Exit" would control the gain of locking with engine torque (analogous to the accel ramps in a standard Salisbury)

[strad]

Electro-hydraulic devices are used in F1 to constantly change the torque acting on both of the drive wheels at different stages in a corner. This torque relationship can be varied to 'steer' the car through corners, or prevent the inside rear wheel from spinning under harsh acceleration out of a bend.

The FIA allows the use of these devices provided that their characteristics are fixed once the car is out on the track. A Moog valve will constantly adjust the friction between the two shafts around the track to maximise the performance of the car dependent on what characteristics have been entered into the on-board computer. The Moog valve opens and closes depending on what the software is telling it to do, but the valve must work to the same set of conditions that are pre-programmed whilst the car is in the pits. This means that the driver cannot actually alter the characteristics of the differential due to a change in tracks conditions for instance, which was allowed in the days of the many driver aids around 1993.

F1Technical
As said by JT..they can increase or decrease the pressure on the clutches in the diff.

[Kiril Varbanov]

El diferencial de un Formula 1 - http://www.youtube.com/watch?v=nsIViNL5w2c

[Dragonfly]

I wish I knew Spanish for that video.
My idea about the diff settings is also what was described above - the three distinctive phases of the period a race car goes through a turn.
What I don't know is whether the limited slip functionality is achieved solely by varying the engagement of the clutch or there are non-traditional gear couples or solutions, which are different than the classic planet-satellite gears, and have a built-in functionality for inherent lower slip when forces back from the wheels differ to some degree. And this functionality is retained even if the active control is not working.

[autogyro]

Electro-hydraulic devices are used in F1 to constantly change the torque acting on both of the drive wheels at different stages in a corner. This torque relationship can be varied to 'steer' the car through corners, or prevent the inside rear wheel from spinning under harsh acceleration out of a bend.

Diff control is not allowed to 'change the torque acting on both rear wheels', that would be traction limiting.
Diff control is allowed to vary the distribution of the torque available from the powertrain asymmetrically through the diff to the rear wheels.

This does allow a small amount of rear steer within the defined operational parameters controlled by the software.
The main benefits are better rear car control under braking and limited control over rear tyre degredation.

I did design a hydraulicaly operated diff that automaticaly compensated for tyre grip and could be electronicaly controlled.
Unfortunately it was a traction limiting device by definition and was not allowed. Shame that.

[strad]

It's like a regular limited slip. but with hydraulic pressure to enhance the normal operation...I believe.

[928S]

It's like a regular limited slip. but with hydraulic pressure to enhance the normal operation...I believe.

Well I know that is wrong, it should never been referred to as limited slip. It is an active differential. What I don't know is why they uses two sets of clutches? My active differential only has one set. An active differential applies the correct slippage needed to get around a corner, under braking and locking when leaving the corner, it doesn't limit the slip. The correct slippage reveres to the difference in wheel speeds when you go around a corner. So in an active diff you have précis slip not slip set up in a predetermined ratio achieved by differential ramps. In my case the slippage is achieved by varying hydraulic pressure, up to 210 bar which is apples to the clutch pack. It can achieve anything from 0 to 100 % locking.

My question is why they have two sets of clutches, is it achieving something like brake steer?

[strad]

My question is why they have two sets of clutches, is it achieving something like brake steer?
928S

Something like..

[Jersey Tom]

In a standard ramp and clutch diff there are two sets of clutches as the axial thrust element is right in the middle. Clutch for the left and right side half shafts

The whole idea is to reduce rear "steer" while on the brakes (i.e. what you get when you have locked / spool rear axle- understeer)

[Tommy Cookers]

IIRC from another thread the diff setting is almost loose or open on corner entry (so not to impede turn-in) and tight or locked on exit (that diff behaviour not causing problems at that point)

isn't the basic diff characteristic in F1 now kept quite simple (to help maintain the traction control ban) ??

[thisisatest]

it is my understanding that the driver has a few predetermined settings he can choose on his steering wheel. the diff is hydraulically controlled, but emulates a "conventional" limited slip differential, a rules requirement.

[Tim.Wright]

Interesting if thats the case. So there are actually no ramps etc, only a hydraulic actuator? Or a combination of ramps and hydraulic preload? Anyone know this for sure?

Tim

[strad]

Electro-hydraulic devices are used in F1 to constantly change the torque acting on both of the drive wheels at different stages in a corner. This torque relationship can be varied to 'steer' the car through corners, or prevent the inside rear wheel from spinning under harsh acceleration out of a bend. The FIA allows the use of these devices provided that their characteristics are fixed once the car is out on the track and settings can't be changed by driver.

TechnicalF1

[autogyro]

Electro-hydraulic devices are used in F1 to constantly change the torque acting on both of the drive wheels at different stages in a corner. This torque relationship can be varied to 'steer' the car through corners, or prevent the inside rear wheel from spinning under harsh acceleration out of a bend. The FIA allows the use of these devices provided that their characteristics are fixed once the car is out on the track and settings can't be changed by driver.

TechnicalF1

This definition is therefore incorrect because it allows full or partial traction limiting.The only way to prevent traction limiting is to state that 'the torque supplied from the energy source must not be reduced but can be applied to each rear drive wheel asymmetrically'.