Clutch Kiss point

[RH1300S]

You could but unless it is done with the driver controling the clutch biting point (correct term) without the assistance of a pre set electronic system

I think that is exactly what they are doing with the levers. I doesn't take much imagination to work out that two levers can do exactly the same job with one overriding the other and vice-versa if they are used together. The system logic could very simply say - whichever lever has most disengagement takes priority. So by holding one fully in and the other partly in - the fully in lever has priority until it passes the position of the partly held lever (which then has priority). In effect it is like any of us taking off in our car and letting the clutch foot up to a precise biting point. The only difference is the driver doesn't have to guess when he has reached that point (his other hand is already there).

My understanding is that there are ways the driver can adjust the clutch settings from the steering wheel - perhaps this controls how aggressively the clutch bites? But these adjustments are made before a start not during.

Those levers are fly-by-wire but effectively operate like a cable or hydraulic clutch lever. Not binary switches.

[Pup]

But 9.2.1 says that multiple clutch devices must have identical travel characteristics and identical mapping. So a second clutch assembly has no advantage.

While 9.2.1 regulates the control of the clutches, it says nothing about the characteristics of the clutch plates themselves, or how much pressure is ultimately applied to them. There might even be an argument that 9.2.1 only applies to the clutch lever, and not any gradual release mechanism within the clutch unit itself.

Then again, perhaps a hand clutch is easier to operate than I thought. There's a lot more travel in DC's video than I thought there was. Works on bikes, after all.

[747heavy]

There is a small difference between a bike clutch (hand operated) and a F1 clutch.
On a bike, you have a force feedback, which is direct related to the clampload in the clutch. On a F1 car the hand clutch is a drive by wire device with no force feedback.
So there is only the position of the lever which the driver can control.
This lack of force feedback, makes it difficult to gauge/control and modulated the release of the clutch.
RH1300S is correct in the discribtion of the system. The two clutch levers are in "parallel", and you could operate the clutch with both of them.
When the driver finds the "bite point" of the clutch, he holds this position, and overrides it with the second lever. When the second lever is released/droped, the clutch comes back to it´s "bite point", with the driver now being able, to modulate the clutch with the second lever.

Now, there is one thing, we need to know about a clutch and a carbon/carbon clutch like used in F1 in particular.
The torque the clutch can transfere is depentend from the following factors,
the effective radius/diameter of the clutch plate (does not change), the number of the friction surfaces/clutch plates (does not change), the clamp load/force of the spring - this is one of the parameters that changes during clutch operation from 0 N
for the fully open/disengaged clutch to max clamp load for the fully engaged clutch.
The clampload is a function of the releaser travel, the release bearing pushes/or pulls on the fingers of the membrane spring, this via a leverage results in a relase of the pressure on the clutch discs. The membrane spings pivots around a ring.
The relation between releaser travel and the reduction in clampload can be linear, but most of the the time it is not.
The other important factor is CoF of the clutch plates. As higher the CoF of the material, as more torque the clutch can transfere. And this is an important point.
In a normal road car clutch the CoF of the clutch plate is fairly constant, and drops with an increase in temperature, fading - similar to overheated brakes.
And here comes the main difference of Carbon clutches into play.
The CoF of carbon/carbon is far from constant and increases with temperature (until very high temps ae reached, and the discs start to oxidate, disintegrate).
It´s similar to an racing tyre on the road.

Now, to start a car with a carbon/carbon clutch, we have the two main parameters which define the torque we can transfere, clampload which is dependend on releaser/pedal position and CoF which depends from the temperature.
In normal conditions the CoF of a carbon/carbon clutch changes from ~0.15 to ~0,57, depenting on temperature and also on the slip (rpm difference). As CoF is a function of temperature and temperature is a function of slip, we have an interesting mechanisem at work here.

So what has all that to do with our starts.
We have two parameters which have an equal large influence on the amount of torque, we transfere, the position of the lever (clampload) and the CoF of the clutch (temperature). To control both at the same time is very difficult, as the relationship is not linear. So what happens?
In simple terms:
- what the drivers does is using the temperature effect to his advantage.
- he sets the clutch to his "bite point" and holds it there with the second lever.
the clutch now slips and why it does so, heats up and the CoF increases, and with that the amount of torque transfered.
When the car has picked up sufficient speed, he just fully engages the clutch, releases the lever. In the start phase the clutch is similar to a slipper clutch.

What is the art is to warm up the clutch correctly, as a difference in temperature will mean a difference in transfereable torque. It is "easy" to control the clampload of the spring via the position of the lever. The remaining variable is the temperature (initial CoF) of the clutch. For the same lever position (clampload) it is possible to have too much or too little torque depending on the CoF/temperature of the clutch.
This is one reason, that sometimes, a driver will make a bad/good start. The lever position is only one variable he can control in the process.

Sorry it´s a long winded explaination, but I hope it makes some sense.

[Pup]

Makes perfect sense; thank you. It also explains how the drivers can stall their car while sitting on the grid before the lights even come on, since they have to find the bite point before pulling back the second clutch lever. A bit too much, and you've stalled it.

[riff_raff]

Top fuel dragsters use a progressive clutch system to the one described. In fact, top fuel cars take the concept even further. They don't use any transmission at all. Instead they use a massive clutch pack that progressively locks up in multiple stages (ie. slips less) as the car accelerates from a standstill and up to over 300MPH.

ECU's are not permitted by the NHRA, so these clutch packs are controlled by a series of timers and relays.

The clutch:


The controls:

[Pup]

Interesting. Strad would know a thing or two about that, I'd bet.

[WhiteBlue]

Top fuel dragsters use a progressive clutch system to the one described. In fact, top fuel cars take the concept even further. They don't use any transmission at all. Instead they use a massive clutch pack that progressively locks up in multiple stages (ie. slips less) as the car accelerates from a standstill and up to over 300MPH.

ECU's are not permitted by the NHRA, so these clutch packs are controlled by a series of timers and relays.

The clutch:


The controls:

Looks like the dark age of dinosaurs and pre digital with a bunch of pneumatic logic. A bit like the Manhattan project in the 21st. century.

[EAKMotorsports]

wow great explanation. thx u guys.

[mach11]

raymondu999 has explained the main points quite clearly. You have to consider that F1 cars start with a semi closed, slipping clutch with a clutch torque well under the full level available from the clutch. The proper clutch torque launch value is pre determined by the driver with his race engineer. The two lever method insures that the driver launches with exactly the pre determined amount of torque and slip. After the immediate launch when the revs have stabilized the driver drops the second lever for full clutch torque and the the slip is eliminated.

I understood how the driver works the paddals.... but i could not quiet understand the part where the slip is involved...

Also, this clutch torque value... what is that???

Have you driven a stick shift car before? You don't just drop the clutch you slowly release it slipping it as you go. Once you have enough speed you can let it the rest of the way out. The two lever system lets the driver drop the clutch to the optimal point between tire spin and keeping the engine in optimal RPM range. the second lever lets him let the clutch the rest of the way out. See if you can find a video of a driver practicing launches and listen to the car it might make it more clear.

I have been watching a few videos... there is a clear distinction when one listens to the car.... i am able to understand the working of this... but when it comes to the actuation part... i am getting confused...

is there any animated vidoes about this... cause i am really interested in learning about it....

this forum is awesome....

[flynfrog]

nothing in the rules says that the levers have to be linear one lever could have a scale that is very exponential so that 80% of the lever is controlling the "bite point" the first and last little bit of travel take care of the rest. The second lever could be linear to let the clutch out the rest of the way


also I have a ton of Top Fuel pics I took a few weeks ago any one interested in seeing them

[WhiteBlue]

I believe that different clutch lever maps are not legal according to § 9.2.1

[747heavy]

I believe that different clutch lever maps are not legal according to § 9.2.1

not different maps, but you can alter the relationship between 0-max (linear, progressive, digressive etc.)
In a simliar way, you do with the throttle.
IMHO- thats what the dial "clutch" on the steering wheel is for.
You give more modulation around the area where the "bite-point" is.
Less releaser travel for x-amount of lever travel.

[WhiteBlue]

Non linear is ok but you cannot set the second lever to a different map as flynfrog suggested.

I reckon you can even have a flat plateau for 50% of the lever travel right in the middle. That would make it easy to hit the right launch torque with the second lever position. In fact that would almost make the clutch lever work like the binary switches which I proposed in the first place. You would find it very difficult to miss the optimum launch point prepared by the engineers.

[autogyro]

F1 engines have a very short stroke and about the same torque as an M3 BMW.
Very little at low revs.
They have no flywheel and a very small diameter clutch pack to gain the most for the engine.
The adjustable biting point pre set dual actuating clutch systems as described, are the only way any sensible form of control can be applied to clutch engagement.
IMO it is hardly a high technology method of establishing inertia to a vehicle, especialy a performance racing car.

[flynfrog]

F1 engines have a very short stroke and about the same torque as an M3 BMW.
Very little at low revs.
They have no flywheel and a very small diameter clutch pack to gain the most for the engine.
The adjustable biting point pre set dual actuating clutch systems as described, are the only way any sensible form of control can be applied to clutch engagement.
IMO it is hardly a high technology method of establishing inertia to a vehicle, especialy a performance racing car.

It works and works well doesn't it. Adding complexity is not always the answer.