Cam sprockets will be made from injection moldable plastic in the Polimotor 2 project to develop an all-plastic engine that will be race ready by next year.
Allegheny Performance Plastics of Leetsdale, Pennsylvania injection molded the net shape cam sprocket from Solvay’s carbon fiber-filled Torlon polyamide-imide (PAI), a very high temperature resin originally developed by Union Carbide. Torlon was the material used to make the engine block in the Ford Polimotor, a project that was done strictly for demonstration purposes.
In Polimotor 2, Solvay will replace up to ten metal engine components – including the water pump, oil pump, water inlet/outlet, throttle body, fuel rail, cam sprockets and others – with parts made from seven of its thermoplastics.
The Polimotor 2, four-cylinder, double-overhead CAM engine will be installed in a Norma M-20 concept car in 2016 to compete at the racing of Lime Rock Park, Connecticut.
Gates Corp., a manufacturer of power transmission belts and fluid power products, performed final machining of the cam sprocket to incorporate a spur tooth design that reduces wear and optimizes transfer of transmission torque between the sprocket and the belt. The Polimotor 2 engine will incorporate two 4-in (102-mm) diameter sprockets, and one 2-in (51-mm) diameter sprocket in its valve train drive system.
Cam sprockets are attached to one end of the cam shaft in an automotive combustion engine and, along with the timing belt, help maintain timing between the cam shaft and crankshaft. Despite constant exposure to high torque, extreme temperatures and vibration, as well as dirt, automotive fluids and road salt, cam sprockets deliver precise timing control to maintain optimal engine performance. If these sprockets overheat, chip, lose their shape or fail to perform reliably under load, everything from the crank to the pistons can quickly cease to work properly.
Cam sprockets are typically made from sintered steel, aluminum or occasionally thermoset phenolic polymers.
Solvay says that its Torlon PAI delivers the highest strength, stiffness and fatigue resistance of any thermoplastic technology up to 525° F (275° C). According to Solvay, the Torlon cam sprocket can deliver comparable mechanical properties with a 75 percent weight reduction over a similarly sized stainless steel cam sprocket that weighs 2.4-lb (1.1 kg).
Unlike metals, Torlon 7130 PAI does not conduct heat, helping to promote longer belt life. It also eliminates potential chipping of the sprocket, which can be a concern when using somewhat brittle phenolic materials.
Torlon was invented more than 50 years ago, but has failed to gain much traction because it is difficult to produce. Molded parts need to be post cured for several days at temperatures up to 260°C (500°F). This allows the molecular weight of the polymer to increase, making the part stronger and more chemically resistant.
Matti Holtzberg is still the lead engineer on the Polimotor project. He is a leading authority on carbon fiber-reinforced composite engine design. His Florida-based company Composite Castings designs and casts carbon fiber engine blocks for global OEMs looking to reduce powertrain weight.