A serpentine belt is simply a belt that is continuous and is used to drive many different devices or parts of a vehicle engine. It was invented by Jim Vance and was first introduced in an automobile by Ford Motor Company in the 1979 Ford Mustang. A very popular addition to a serpentine belt drive system is a supercharger. Supercharger pulleys are used to rotate the impeller within the supercharger, which forces air into the engine and effectively raises the horse power potential. One of the largest drawbacks of a supercharger is the amount of slip between the belt and the pulley. Slippage occurs when the driven belt slips off or creates a “hiccup” in the system, which can cause a loss of power from the engine. The Carbinite Metal Coating was initially used to increase the life expectancy of dies and other tools used in manufacturing. Carbinite Metal Coatings have been proven to be useful in many circumstances, from tread on metal steps, to tooling applications.
The slippage that acts on the pulley however plays a major role in the effective horse power that is lost. The difference in slippage is to be tested between two pulleys. One pulley has a Carbinite Metal Coating on it which will help decrease the amount of slippage that acts on the surface of the pulley while the other pulley is just a standard pulley. The pulley that will be observed and compared to other ‘standard’ pulleys is one with a non-slip coating to reduce the amount of slip. Two methods are described below to show the better performance of the Carbinite coated pulley over the uncoated pulley. Both of the testing procedures are based on static slippage tests which will be further verified by using dynamic slippage tests in the future.

Method 1
The static testing was performed using three different left-hand tensions of 50, 75, and 125 ft-lbs (Testing Apparatus as shown in Figure 1 above). Each increment was performed five separate times to obtain an average for each increment. The results for the coefficient of friction were obtained approximately 1.29 and 0.7 in averages for each tension that was applied for the coated and uncoated pulleys respectively. This shows that the coated pulley has a coefficient of friction that is 1.8 times greater than an uncoated pulley. With this it has been proven that the coated pulley will not slip as easily as the uncoated pulley. The next step would be to determine whether a dynamic test would provide similar results.

Constant tension was loaded on one side of the pulley, which was small loading relative to the other tension. The opposing tension was varied until slip occurred. Once the general tension was acquired where the pulley would slip, the load was relaxed, and then weight was added back on in small increments to get a more accurate value for the tension just before slip occurred. This process was repeated 5 times for each pulley, with each trial using a different constant tension.
The average belt tension ratio for the standard and the Carbinite pulleys are 9.14 and the 48.96 respectively. The average static coefficients of friction for the standard and Carbinite pulleys are 0.7 and 1.24 respectively which shows that there will be approximately a 1.77 times greater coefficient of friction in the Carbinite pulley compared to the standard. Also, the tension ratio in the Carbinite pulley is approximately 5.32 times greater than the uncoated pulley. It can be seen that the standard pulley begin to slip at lower tension ratios than that of the Carbinite pulley which also shows that the force or torque needed to create belt slip is substantially higher in the Carbinite pulley, showing a good range of performance benefit. Since the Carbinite pulley has more than 1.7 times the friction, and can handle more than 5 times the tension difference than that of the standard market pulley. This result shows that the pulley has real potential for supercharged vehicle applications. The higher the coefficient of friction is the less slip the pulley will receive. Less slip will translate into more horsepower for an engine, which will result in performance. Being that no everyone will understand how this experiment was carried out or what the results mean, a percentage was calculated for the increase of coefficient of friction. The Carbinite pulley has 70% increase in coefficient of friction resulting in far less slip than any other standard pulley on the market.

Acknowledgements:
Experimentation was conducted at – and partially supported by – the Department of Mechanical Engineering at Youngstown State University and Carbinite Metal Coatings. This project was completed by YSU mechanical engineering students (Spring 2009/MECH 3762- Machine Design) as their design projects under the supervision of faculty advisor Dr. Yogendra Panta.