Clutch Heat Shield question..

[JustinJ99]

Dismissively I was so glad to be done with Thermo in school, I sold my textbook back. Now I wish I hadn't.

We're working on a slipping clutch for VERY high performance drag racing applications and the problems always arise in the heat shield. The structural elements are all titanium while the friction surface contacts are Grade 50 steel. Friction surfaces are mounted to the structural titanium using 48 grade 8 bolts, and it is one solid piece of steel about .300" thick with six symmetrical grooves cut in it. Anytime the clutch is slipped just a little too much, the steel warps .003 to .006 from it's original flatness, rendering it useless.

My theory is that the heat is staying in the steel and is not able to use the mass of the structural titanium to help dissipate the heat because the conductivity of the steel. Other clutches similar to this use 6 or 9 individual steel pads instead of one piece heat shields that are even thinner, which I think will help our problem with expansion and contraction being a factor, but the question is will it help make the titanium a better heat sink for the steel?

Anyone have any ideas?

 

[chicopee]

About having a clutch plate with inner cooling passages in the shape of radial or curved blades? the center of the plate would be hallow out for air to enter. Air would exit from the plate outer perimeter. Any such plate in drag racing?

 

[JustinJ99]

I've thought about doing that actually. The biggest problem is that the clutch is set in a very enclosed environment. Even spinning in excess of 10,000 RPM's, which gives the outer diameter a speed of approx. 270MPH, the air isn't freshly circulated. To my knowledge, there has been no such configuration ever made.

I think the problem with air slots on the structural side has been the integrity of the steel when you maintain a one-piece heat shield. The plate loads exerted are in excess of 3 tons and the slipping of the clutch creates enough heat to make the steel glow bright red.

 

[EdDanzer]

Cooling should be provided for if you ever hope to have a functional system. One calculation to put cooling into perspective is to convert the horsepower being slipped into BTU’s. This will provide a cooling value. It may be wise to try compresses liquid CO2 for cooling as the amount of heat to remove could be several thousand BTU’s per second.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[chicopee]

CO2 may be too cold on the plate when the clutch is initiated but may be prcooling the X-mission housing with ice could solve this problem.
I dont drag race however it is my understanding that some drag racing engines are cooled with ice in order to dispense with a water cooling system. Is that true?

 

[JustinJ99]

In some circumstances yes. Pro Stock cars are the only "Pro" class that are equipped with radiators and they all have "Ice Boxes" filled with ice and water. They circulate the coolant for rapid cooling. The application this is for, it is using about 13GPM of methanol for fuel at wide open throttle, about 526 cubic inches of motor and uses a massive screw style supercharger. Ice actually forms on the throttle body "butterflies". The engine might be running for a total of one minute, including the 6 seconds of wide open throttle for the run.

We have thought about introducing CO2 into the bellhousing, as they already use compressed CO2 to shift the gears in the transmission. Most of the heat is generated in the fisrt half second of the run, where the clutchslips the most. It then slips slightly at each of the gear changes as to not knock the tire loose as the 4,000 horsepower engine continues to accelerate.

I think we may have solved the problem of the warpage by making the heat shield segmented instead of keeping it one soild piece. At 10,000 RPM's, the titanium wants to flex a little, which also flexes the steel heat shield. As the steel and titanium expand, contract and flex at different rates, as well as conduct heat at incredibly different rates, the titanium always returns to it's normal shape and the steel, being exposed to the brunt of the heat and friction, is a slave to what the titanium wants it to do. I was told by three friends of mine who have been doing clutches for these blown alcohol and nitromethane powered vehicles for some time and they confirmed my suspiscions.

 

[chicopee]

I get the impression that this is a single plate clutch, therefore wouldn't a multiple plate clutch be better, meaning that the first plate would get red hot as you described but the successive plates wouldn't get as hot?That ice in the throttle was a problem that I experienced with my VW Bug back in the 60's during humid days.

 

[JustinJ99]

Oh no, this is a three disc/two floater plate clutch about 9.5 inches in diameter. Drag racing clutches are interesting because most of the classes do not allow for traction control mechanisms, so the lever assisted slipper clutch becomes their traction control.