How can you lock the rears?

[peanutaxis]

without stalling the engine?

[Robbobnob]

'locking' the rears generally refers to the term when the rear tyres are under rotating for a given car speed - e.g. the tryes surface velocity is slower than the cars velocity. Also F1 cars have an anti stall system, however I am unsure whether this would kick in in such a situation.

What usually happens is one tyre will 'lock' when the contact with the surface lifts - over a bump under braking - or when braking on a slick patch - such as the white line in Massa's incident. Once the tyre loses its static friction with the ground it has less grip and causes the rear to rotate.

[Tommy Cookers]

'locking' the rears generally refers to the term when the rear tyres are under rotating for a given car speed - e.g. the tryes surface velocity is slower than the cars velocity.

well said !!

locking flatspots the tyre, under-rotating doesn't
99% of the time when they say locking it's really under-rotation

also remember the diff action is open or nearly open on entry to most corners, especially in the wet
so locking one rear wheel wouldn't stall the engine

[autogyro]

locking flatspots the tyre, under-rotating doesn't
99% of the time when they say locking it's really under-rotation
also remember the diff action is open or nearly open on entry to most corners, especially in the wet
so locking one rear wheel wouldn't stall the engine

Yes and flat spots occur on the front tyres and only very rarely on the rear tyres and then usualy only when the car is spinning or the engine does stall.

[peanutaxis]

Hmmnn. Seems a bit weird that ABS and traction control, stability control are banned but fancy diffs are in. It bucks the trend.


I don't think Massa's accident was because of the paint. The point at which Johnny Herbert stopped the video when Massa's front wheel was almost on the paint he was steering 90 degrees to the right, meaning that his rear wheels were off to the right also.

[Cold Fussion]

Hmmnn. Seems a bit weird that ABS and traction control, stability control are banned but fancy diffs are in. It bucks the trend.

Are the fancy diffs a closed loops system though? That would be a critical difference.

[peanutaxis]

Are the fancy diffs a closed loops system though? That would be a critical difference.

Not that sure what you mean but apparently the diffs are free on entry to corners and stiffen up in the exits. That's quite a manipulation.

[raymondu999]

Are the fancy diffs a closed loops system though? That would be a critical difference.

Not that sure what you mean but apparently the diffs are free on entry to corners and stiffen up in the exits. That's quite a manipulation.

Indeed. The diffs are open loop. For those unfamiliar with the terminology, open loop means it does as its told. Closed loop means it does as its told, then readjusts itself according to external stimuli. For example, traction control activates and adjusts itself to the detected amount of wheel slip.

[peanutaxis]

[quote="peanutaxis"
Indeed. The diffs are open loop. For those unfamiliar with the terminology, open loop means it does as its told. Closed loop means it does as its told, then readjusts itself according to external stimuli. For example, traction control activates and adjusts itself to the detected amount of wheel slip.

So I imagine the diffs react to a change from zero throttle to some throttle and stiffen up. Would that be open or closed?

[thisisatest]

the electronic diffs are only allowed to emulate mechanical ones. the electronic switching is the effect of putting in a limited slip diff with different plate, ramp, and preload settings. within a given setting, they change in "locking" friction based on driving and braking torque.
this is open-loop.

[raymondu999]

[quote="peanutaxis"
Indeed. The diffs are open loop. For those unfamiliar with the terminology, open loop means it does as its told. Closed loop means it does as its told, then readjusts itself according to external stimuli. For example, traction control activates and adjusts itself to the detected amount of wheel slip.

So I imagine the diffs react to a change from zero throttle to some throttle and stiffen up. Would that be open or closed?

Nah - that's still "reacting" - and in my book that means open loop. Not sure how the regs view it though.

[autogyro]

I am not even sure that most F1 powertrain engineers know what the difference is.
It seems to change depending on who is reading the regulations.

[thisisatest]

if it stiffens up with an increase in torque, it's still open loop.
if the diff, say, senses the need for a tighter turning radius and opens some to allow greater wheel speed differential, that is closed loop.
i think.
according to wiki, it is sometimes subject to interpretation.
the way i see it, you increase torque, the diff stiffens up always. did you want it to stiffen up? maybe not. the diff doesnt care. that is open loop.

[raymondu999]

The way I define it is a stubborn system that refuses to change unless you give it a direct order. Indirect inputs such as throtlte opening is counted as closed loop. But then again, the FiA ruled DDRS legal last year - which does imply that they are considering only primary inputs and not indirect secondary ones

[autogyro]

The problem next year will be the increased energy that needs to be controlled from energy harvesting.
If the diff control remains as it is, it will be nigh impossible to control the rear of the car during deceleration and turn in and rear tyre wear will be almost uncontrolable. (see Pirelli tyre thread and Fric)
Open loop diff control is the ideal place to develop better control over these problems but it will by default include open loop operation and therefore traction control.
At the moment the only area of development looking at controlling rear tyre traction is Pirelli with their seriously limited tyre testing arrangements.