RPS Clutch
RPS – Information
Clutch Action
A clutch’s main purpose in life is to smoothly transfer power from the engine to the wheels. It does no one any good have 500 horsepower at the engine if you can not get that power to the wheels. Automotive clutch systems are basically made up of three parts: the pressure plate (clutch cover), the clutch disc, and the flywheel. The pressure plate is bolted to the flywheel which in turn is bolted to the crankshaft. The clutch disc is attached to the transmission thru a hole in its center. When the clutch is engaged the disc is squeezed against the flywheel by the pressure plate, and when the clutch pedal is pushed to the floor the disc is spinning freely between the pressure plate and flywheel.
The amount of torque or power the clutch can transfer from the engine to the wheels depends on how hard the pressure plate squeezes the disc, how big is the disc, how sticky is the disc, how sticky is the flywheel, and how many discs are being used. The larger the disc, the more power it can transfer. Unfortunately most of today’s cars have very small transmissions and very little room to make the disc bigger around. Increasing the clamping force of the pressure plate is a great way to increase a clutch’s torque capacity.
There are a number of ways to do this including moving the fulcrum or pivot point that the diaphragm spring rides against. This method is used when you only need a small increase in pressure to give a modest increase in holding power. (Fig. A)
Another good way to increase torque capacity is to replace the diaphragm spring with a stronger unit. RPS uses their patented (#5,769,973) technology to increase the strength of the existing spring while erasing any memory of the stock spring. RPS also uses their unique proportional dual diaphragm pressure plate technology that allows them to set the clamp force to any desired pressure within 100 lb increments. (Fig. B) ACT replaces their springs with thicker one piece units.
Stickier clutch discs are another way to hold more power. There are many different materials to choose from, but the most important thing to consider is the balance between good holding power, drivability, and clutch life. As a rule of thumb full face organic discs provide the smoothest engagement and the longest life. Puck style discs hold more power that street discs and can take more slippage and heat generated by harder driving. The fewer the pucks the more power the disc can hold. Four puck discs can hold more than six puck disc, but because they have less material a four puck disc will wear out faster than a six puck. Since puck style discs are stickier than organic disc, they are usually less driver friendly. One way to improve the drivability is to make sure to use a sprung hub puck discs. Solid hub discs are strictly for racing (less weight) and are not fun on the street. Puck style clutches are also harder on their opposing surfaces, like the flywheel and pressure plate casting. One novel way to address this problem is RPS’s CYN-R-G
Segmented Flywheel (Fig. D) and Pro MAX pressure plate (Fig. C). Both of these use a unique segmented heat shield system that allows for better heat transfer and replaceable parts for the life of the car. As most drag racers know, they have to replace their pressure plate every time they replace their puck style disc because the disc has worn a groove to large to machine out. The Pro MAX pressure plate uses steel pucks that are more wear resistant than standard cast or ductile iron unit and they are replaceable.
Because of the rapid advancements in horsepower numbers, tire combinations and suspension systems, there has been an equally rapid demand for better and better clutch systems. One company, RPS feels they are leading the way with their Turboclutch Carbon (Fig. E) and Ti Carbon (Fig. F) line of ultra performance clutches. Carbon-carbon is used in Formula One for their brake and clutch systems. It is also used by Top Fuel, Funny Car and Pro Import racing for their brake systems. The advantages of carbon-carbon are many, including smooth engagement, high heat capacity, light weight discs, and long life.
RPS – Separating the facts from friction!
Clutches are basically made up of two parts: the pressure plate (clutch cover) and the clutch disc. A clutches main purpose in life is to smoothly transfer the engine’s power to the wheels. The following is the actual formula used to calculate the amount of torque the clutch system can transfer.
Clutch Torque Capacity: Pressure plate strength, times clutch disc size, times the number of clutch discs, times the friction coefficient, divided by a constant.
By looking at this equation, we can see that torque capacity increases by doing any of the following: increase the strength of the pressure plate, increase the size of the disc, install more discs, and increase the coefficient of friction of the disc. In most cases, it is not practical to install a larger clutch or go to double or triple disc set-up so the two areas a clutch engineer has to play with is making the pressure plate stronger and increasing the coefficient of the disc.
Mechanically it is important to understand how a clutch is attached to the engine. Since the pressure plate is bolted to the flywheel and the flywheel is bolted to the crankshaft, then the flywheel, pressure plate and crankshaft all turn as one. The clutch disc has a hole in the middle with splines which slides over the transmission’s main input shaft. All of the engine’s torque is transmitted though the clutch disc to the transmission and then to the wheels.
When the clutch is engaged, the pressure plate squeezes the disc against the flywheel making the disc rotate at the same speed as the engine. When the driver presses down on the clutch pedal to disengage the clutch, the casting surface of the pressure plate (the surface that the disc rides against) pulls away from the disc and releases the disc from the flywheel. The flywheel still spins, but the disc and the transmission input shaft do not. This is why a car can be stopped with the engine running while in gear.
Going back to the above equation, if we increase the clamping force of the pressure plate, then we increase the torque capacity of the clutch system. Almost all of the pressure plates used today use a diaphragm spring to exert its clamping force. Over the years clutch companies have tried various ways to increase clamping force. One of the most recognizable methods is using the centrifugal force of weights attached to the fingers of the diaphragm spring. There have been many arguments over the years if this technique really works or is it just great marketing at work. There is no reason to get into the debate here, except to explain how to test the theory yourself. The faster the weights spin, the higher the centrifugal force. If the force is directed in the direction of pulling back on the diaphragm fingers, then the clamping force will go up. To test if the force is in the right direction, pump the clutch pedal at idle and feel how stiff the pedal is. Then rev the engine to near redline and pump the pedal again. If the centrifugal force is pulling back on the fingers, then the pedal will be stiffer at the higher RPM.
Another old-time method of increasing pressure plate pressure is to move the fulcrum point or pivot point that the diaphragm spring rides against. The spring acts as a lever with the pivot point of the lever being the fulcrum. With the help of leverage, a lever allows you to lift a heavier object than without leverage. Moving the pivot point closer to the object requires more movement at the other end (longer stroke), but gives you more leverage.
So the only down side to more leverage is a longer stroke. When you move the fulcrum point in a pressure plate you get more clamping force, but you also have to stroke the clutch pedal farther to get it to disengage. Poor release characteristics are the most common complaint you will get when using a pressure plate that has had the fulcrum point moved.
The RPS method in the 90’s to increasing pressure plate pressure is to re-shape the diaphragm spring to produce a higher spring force. This method has been so successful that it has been patented. When re-shaping a diaphragm spring it is critical that the original shape has been "erased" from the metal’s "memory". If you just re-shape the spring without employing the patented step to eliminate the memory, over time the spring will bend back to its original shape.
Now, most RPS Max Turbo Clutches that are a push type are a progressive dual diaphram technology. This innovative technology gives the pressure plate, maximum release, less diaphram friction, serious holding power with smooth engagement, and custom Pressure Plate build-up is available in 100 lbs increments! Turbo Clutch also provides patented 7 stage heat treatment to all pull style Max pressure plate. This provides the diaphram to have the highest clamp load with prolong use without sacrificing good release or durability.
Another area that clutch engineers have available to them is changing the coefficient of friction of the clutch disc. Raise the coefficient and raise the torque capacity. However, the problem most engineers have is that there are only a few clutch disc manufacturers in the world. Most of the aftermarket performance clutch manufacturers like Centerforce, Ram, Mcleod, Zoom and others can only buy the same friction materials from the same manufacturers.
The "dual friction" or "puck" style clutches use either cut pieces of factory material or ceramic or Kevlar segments. The up side of the puck design is better holding power. The reason for the better holding power is the pucks have about half of the surface area of a full circle disc so the pressure plate pressure is distributed over a smaller area. You can increase pounds per square inch (PSI) by leaving the pressure the same and decreasing the square inches. Of course the less material you have the faster the clutch wears out. The down side of ceramic pucks is they not only wear themselves out, but they can be hard on the flywheel surface. Aftermarket FW’s have many friction metal’s that are different co-efficient of friction surface that the disc mates to. Cro-moly FWs are durable in structure and lightweight but the material are hard on the Rockwell scale. This causes the friction surface to lose it’s co-efficient of friction grip and cause more slippage than normal O.E.M. cast iron. The same applies to heat treated steel friction inserts.
The highest technology known to man in fiction surface is Carbon-Carbon. Carbon-carbon composites consist of highly-ordered graphite fibers embedded in a carbon matrix. C-C composites are made by gradually building up a carbon matrix on a fiber preform through a series of impregnation and pyrolysis steps or chemical vapor deposition. C-C composites tend to be stiffer, stronger and lighter than steel or other metals. The most important class of properties of carbon-carbon composites is their thermal properties. C-C composites have very low thermal expansion coefficients, making them dimensionally stable at a wide range of temperatures, and they have high thermal conductivity. C-C composites retain mechanical properties even at temperatures (in non-oxidizing atmospheres) above 2000°C. They are also highly resistant to thermal shock, or fracture due to rapid and extreme changes in temperature.
Our hard core clients who uses our C/C technology are racers that are utilizing this amazing break-through by doing 2nd gear burnouts, 2nd gear launches, line lock assisted launch with the clutch semi disengaged to load the engine to make positive boost 15~30 psi in 2nd gear!!! Others do 1st gear 7000+ RPM clutch dumps to get the clutch to slip for a fraction of a second for it not to break the tires loose. All on a 2 ton AWD car making 750+AWHP 200+ times at the track daily driven (3000GT-VR-4 Dynamic Racing), Supra 2JZ with 1200lbs of torque on a dyno slipping (Powerhouse/MVP), Viper GTS Supercharged cranking out 1000lbs of torque daily driven (Palo Castalano/ Heffner Performance) to name a few.
Currently this material is available only from RPS Performance Products.
I see the confusion that some of these peoples judgment are being made. The Exedy or OS Giken or ATS and any one else except for Tilton is using the technology RPS created 5yrs ago (CarbonClaw). This stuff is a carbon with ceramic mixture and will be a higher coefficient than the regular friction materials available to them. The Semi-Carbon is what the true name is called, cause of the friction mating surface is metal and can be very costly to manufacture even in this technology. But the affect is still the same way of conventional clutches not holding up to heat and will glaze over if slipped too much. The disc that is carbon will glaze over, hence it is more streetable when it heats up, therefore will not hold up to the higher boost it will slip itself to death. The product’s technology is still a long shot away from the real McCoy Carbon-Carbon. This is the only stuff that NASA, F-1, Top Fuel, WRC, and NASCAR use.
RPS
RPS – Movies
Ryan Woon Wins the 2004 National Supra Meet 6 speed Challenge with a 9.80@146.77 MPH. – Click here to view the movie
SW runs a 9.35 at 149 mph in Peter Blach's 1998 Supra with the RPS Twin Disc Carbon-Carbon clutch. 1.305 60 ft!!! 1-26-2005 – Click here to view the movie
Eagle Talon Turbo runs 10.0 second pass using RPS Billet Twin Disc Carbon Carbon. – Click here to view the movie
300 ZX TT, 5 speed using RPS Twin Disc Carbon Carbon clutch - 10.60 @ 133 MPH. – Click here to view the movie
300 ZX TT, 5 speed using RPS Twin Disc Carbon Carbon clutch runs - 10.89 @ 128 MPH. – Click here to view the movie