Clutch mounting?

[xpensive]

Dave Killens,
...
Friction clutches are designed by thermal capacity, and not so much by an ability to transmit torque. If torque transmission was the only concern, then a single clutch plate could be made to work by increasing the clamping force. The reason multiple plates are used is to provide enough thermal mass to prevent the temperature rise in the plates during slippage from exceeding safe levels for the CRC plate materials. The reason small diameter plates are used is to minimize the polar inertia of the clutch pack and to keep the engine CL as low as rules permit.

The AP drawing I linked is for a 115mm (4.5 inch) dia clutch, which is quite small. I believe current rules require an engine crank CL at least 58mm above the reference plane (ie. the underwing OML). So a 115mm dia (57.5mm radius) clutch pack would seem appropriate

I'm afraid that I'm with Edis here riff, when torque capacity can be simplified as follows;

Torque-max = mu * Axial force * (outer radius + inner radius/2)

If Torque is 300 Nm (750 Hp at 18k), OR is 58 and IR is 43 mm like the AP, mu set at 0.6, you need a force of 10 kN
to transmit the torque through one friction surface, 5 kN with two and only 1.4 kN with seven surfaces as the AP.

When looking at the very simple spring loading device of the AP-clutch, I would think that such a low clamping force
as 1.4 kN (320 lb) is most advantageous for packaging and almost everything else.

Come to think of it, the above is of course another reason to standardize crank centerline.

[riff_raff]

xpensive,

Thanks for the reply.

However, consider this: That 7 disc (4 stator/3 rotor) 4-1/2 inch clutch pack has about 1 lbm of carbon. That carbon has an oxidation limit of about 1500 degF and a specific heat value of around .17 Btu/lbm-degF. And those carbon clutch discs are fairly well isolated thermally, so there's not much heat rejection.

If one assumes that those carbon clutch discs must absorb an average of maybe 200hp for about 3 seconds (ie. around 25,000 Btu) without exceeding a temperature rise of maybe 1400degF, it becomes apparent that thermal mass is of great concern.

Regards,
riff_raff

[xpensive]

riff_raff;
Lets see, when graphite has a heat capacity of 0.69 kJ/kg*K, 200 Hp (147 kW) over 3 seconds, 440 kJ,
will heat 1 lb (0.454 kg) of graphite to 1400 C in theory.

However, 3 seconds of slippage sounds like cooking to me, be surprised if it's more than one second in reality?

But all in all, I think it's safe to say that you need the seven surfaces for torque as well as heat dispersion.

[autogyro]

Sorry it does not depend on the torque available to transfer.
It depends on the capability of the tyres to maintain traction during clutch apply and the mass of the vehicle. A million ft ibs with F1 weight would simply see the wheels spin. The clutch would be fine.
It also depends to a great extent on the 1st gear ratio.
A very low ratio will result in little problem for the clutch.
Extremely low and you would barely need one plate.

[xpensive]

Sorry it does not depend on the torque available to transfer.
It depends on the capability of the tyres to maintain traction during clutch apply and the mass of the vehicle. A million ft ibs with F1 weight would simply see the wheels spin. The clutch would be fine.
It also depends to a great extent on the 1st gear ratio.
A very low ratio will result in little problem for the clutch.
Extremely low and you would barely need one plate.

Sometimes Gyro, I wonder if your keyboard is located in another universe or something, 'cause I don't have the faintest of what you are trying to xpress here?

[riff_raff]

xpensive,

Heat transfer and friction with carbon is a tricky subject.

As I noted, carbon-carbon definitely has an oxidation temperature limit. With a clutch pack, the heat is being generated at the sliding interface and must be transferred away from that surface. Pitch based carbon has good heat transfer in the axial direction, but poor heat transfer in radial direction. So getting a good heat conduction path out of a thick stack of rotors and stators can be troublesome.

With regards to Mu, carbon has a friction coeff. that varies with temperature. It is the opposite of most materials in that its Mu increases with temperature. Carbon clutches tend to slip very briefly until they heat up. Then the Mu increases and they quickly grab, almost like an on/off switch. That's why even very good drivers still occasionally stall leaving the pits.

Regards,
riff_raff

[xpensive]

Just a few remarks riff;
- Obviously every clutch has a problem with dissipation of heat due to its physical location and lack of conveying medium, but graphite or carbon having different heat-transfer properties depending on direction is a new one to me?

- I agree that an F1 clutch is an on-off thing, why I honestly believe that your starting values of 200 Hp for 3 seconds is way off the mark, my late mom used to do that with her Volvo 121 but not with that kinda power.

[noname]

- Obviously every clutch has a problem with dissipation of heat due to its physical location and lack of conveying medium, but graphite or carbon having different heat-transfer properties depending on direction is a new one to me?

Carbon fibers can transfer heat quite well, but that's not the case with the resin. That explain reasonable heat transfer along fibers and poor in the opposite direction.

As an example (from area closer to me than race cars); bike industry is working a lot on the resins being able to withstand high temperatures so fully carbon wheels would provide similar braking performance as the alloy ones. Airbus is also working hard to be able to create heat/flame resistant composite structures.

[xpensive]

That makes perfect sense for a resin-matrix composite, but my understanding is that carbon/graphite brakes and clutches are made through a HIP-process (Hot Isostatic Pressure), with no particular orientation of the fibers?

[747heavy]

It don´t think that there is any resin used in carbon clutch plates or brake disc´s.
There are different matrixes with different fibre orientations used.
Most common for F1 clutches are 3D matrixes now, but there where experiments with other orientations and 2D Matrixes where used in the past.
Burst resictance at high rpm beeing one problem, but not too much in an F1 clutch due to the small diameter.
Heat transfer axial to the fibre is better then radial to the fibre.

[noname]

I've tried to find some information and all I got is carbon-carbon composites are being used as a brake/clutch discs material. Description of the process (as well as the materials' name) suggests carbon acts both as a matrix (in a fiber form) and a "resin". However I have to admit descriptions I've found were so general and that, together with my understanding of the fibers' manufacturing being not so good, means I only suspect that my be the case.

Would be nice if someone more familiar with the topic gave us more thorough explanation.

[marcush.]

this is how Carbonbrakediscs are made:

The brake material is made from chopped carbon cloth made from fibers obtained from petroleum pitch. Typically a carbon cloth is pre-pregged using phenolic resin. The objective of the resin is to hold the fibers in the particular orientation. In pre-pregging operation the resin is partially cured to remove most of the solvent. After partial cure, the cloth is chopped into small squares or donut shaped as desired.

The pre-preg cloth is then arranged in the required direction in a mold. This is a manual and laborious process. The mold is then taken to temperatures around 300-350C and high pressure to mold the part. The molded part contains fibers and cured resin. However, cured resin still has non-carbon components, that would affect properties adversely.

The molded disks are carbonized to remove all the non-carbon species. This is followed by graphitization step, where disks are cured to temperature in excess of 2000C. The porosity in the disk at this step is approximately 30-50%. This porosity is then densified using a process called Chemical Vapor Infiltration (CVI). In this process, natural gas cracks at temperature around 1000C to deposit carbon.

So the carbon brake actually have only carbon ,although at the start of it there is resin involved.

[747heavy]

some info can be found here.
F1 clutch disk are not made from chopped fibres, they where at a time, but did had poblems with burst at high radial speeds.
Radial Speed is not so much a problem on brake discs´s:

The most temperature sensitive element of an F1 clutch is the spring,not so much the carbon material in itself. But wear will increase dramaticly at > oxidation temperatures. But this is normaly not the main problem in a clutch application.

High wear due to excessive temperatures can be seen sometimes with carbon/carbon brakes during races, when the cooling duct size was set wrong, or the ducts got blocked during the race.

http://www.compositesworld.com/articles ... -cc-brakes

http://www.compositesworld.com/articles ... ping-power

http://www.sicom-brakes.com/DMC_-_Prasentation1.pdf

http://www.freepatentsonline.com/7413701.pdf

[747heavy]

I stand corrected, there are resins used in carbon clutch/brake disc´s, but the process if different from typical fibre/resin composite system.
This descripts cabon/ceramic discs, but the production process for carbon/carbon is similar.

courtesty of SGL group:

>>>>





Carbon-Ceramic Clutch Plates

Material:
Carbon-ceramic clutch plates are made of woven carbon fiber material which will be converted together with resin into carbon fiber reinforced plastic. Further process interactions are carbonizing, compaction and siliconizing. The siliconized material can only be formed by jet cutting and wet grinding.


Characteristics:

* Low density (2,0 g/cm³)
* High strength
* Low abrasion in long life terms
* High temperature resistance and thus improved friction performance and
high energy density with small installation space
* Low thermal expansion
* Good friction performance


Use:
Carbon-ceramic clutch plates are used in dry-running multiple disk clutches. Due to the fact that the production and the maintenance of parts of this construction method are much more time-intensive and more expensive, these clutches are generally only build into race or rally cars. However, the most variation possibilities exist for this kind of clutch. The reason is that there are more than one friction surface available and thus the entire friction surface can be adjusted by changing the clutch inner plates and carrier plate as well as the diameter. High power transmission and misuse security are characteristical for this kind of clutches.

The most efficient multiple disk clutches consist of a titanium cage and clutch plates made of carbon fiber reinforced carbon and are used for example in the Formula 1. The advantages are the high temperature resistance of the used CFC material and the energy density which can be built into a small installation space.
Disadvantages of these clutches are the significantly fluctuating friction value over temperature, compression and sliding speed. Because of this factor the use in series cars is impossible. The relatively high abrasion would lead to short life time and would only cover a service performance of 5,000 to 10,000 km.

An advancement in this sector is the multiple disc clutch of the Porsche Carrera GT. It consists of two carbon-ceramic drive plates (170x6 mm) and three inner plates with organic friction pads. With this super sports car it was possible to proof road-worthiness of the friction couple and to reach a life time of 100,000 km.

Carbon-ceramic clutch plates are also used in Le Mans long distance race cars as well as in Paris-Dakar rally cars. Friction partner in these cars are pads made of organically bounded multi-component mixtures or sintered metal.

<<<<<

[riff_raff]

xpensive,

There are two common types of Carbon Reinforced Carbon (CRC). Pitch based and PAN based. Pitch based CRC is made from petroleum/coal pitch precursor. PAN based CRC is made from Polyacrilonitrile textile precursor.

Clutches and brakes mostly use pitch based CRC because it is tougher and more suited for the application. I not much of a chemist, but I believe the reason pitch based CRC has higher thermal conductivity in a given direction has to due with its manufacturing process. The finished material has an "un-isotropic" fiber structure, and the thermal conductivity tends to be better along the axis of the fibers.

There are sometimes resins or binders used in the initial manufacturing process of CRC materials, but the finished product is pure carbon.

Regards,
riff_raff