Solvay’s PAI drives new, all-plastic engine closer to reality with lightweight cam sprocket

A project to manufacture a next-generation, all-plastic engine for competitive racing has chosen a polyamide-imide (PAI) from Solvay Speciality Polymers to replace conventional metal in the fabrication of a new cam sprocket design.

The Polimotor 2 project, which is led by automotive innovator, Matti Holtzberg, and is the follow-on project from the original Polimotor project in the 1980s, aims to develop a next-generation, all-plastic, four-cylinder, double-overhead CAM engine that weighs between 63-67 kg, or about 41 kg less than today’s standard production engine.

The new cam shaft sprocket design used in the engine, which will be used for competitive racing in 2016, is made from carbon-fibre filled Torlon PAI from Solvay, a material which contributes to the overall lightweight of the engine.

“Solvay’s Torlon PAI played a vital role in the success of our first Polimotor engine during the early 1980s; and the breadth, performance and versatility of the company’s materials technology has definitely expanded since then,” said Holtzberg, who is also President of Composite Castings, LLC, based in the US.  

“Solvay’s continuing advances offer the basis for even greater innovation in Polimotor 2 today, where its carbon-fibre filled Torlon PAI enabled development of a mechanically strong, but extremely lightweight cam shaft sprocket. This is only the first of several new breakthrough applications using Solvay’s advanced materials technology that we expect to announce in the coming months.”

Cam sprockets are typically made from sintered steel, aluminum or occasionally thermoset phenolic polymers. However, Polimotor 2 opted to mould its engine’s spur tooth cam sprockets using Solvay’s 30 percent carbon fiber-reinforced Torlon 7130 PAI – an ultra-high performance grade launched by Solvay long after Polimotor’s earlier iteration during the 1980s. The spur tooth design reduces wear and optimises transfer of transmission torque between the sprocket and the belt.

As a class of materials, Solvay says its Torlon PAI delivers the highest strength, stiffness and fatigue resistance of any thermoplastic technology up to 275° C. Torlon 7130 PAI, in particular, delivers the portfolio’s most optimal balance of these mechanical properties, with a specific strength of 1.4 105 J/kg and specific stiffness 15 106 J/kg. Stainless steel, in contrast, delivers specific strength and stiffness of 0.8 106 J/kg, and 24 106 J/kg, respectively.

In practical terms, Solvay explained that this allows the Polimotor 2 cam sprocket fabricated from Torlon 7130 PAI to deliver comparable mechanical properties with a 75 percent weight reduction over a similarly sized stainless steel cam sprocket that weighs 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 phenolic materials because they are more brittle. Lastly, Solvay’s high-performance PAI delivers excellent fatigue resistance and outstanding wear performance at elevated pressures and velocities, thereby decreasing noise and vibration, and offers broad chemical resistance to automotive fluids.

 “One of the highest performing polymers in Solvay’s automotive portfolio, Torlon PAI has a proven track record of success in commercial automatic transmissions and dual-clutch transmissions, where higher pressure and velocities require higher temperature materials with excellent strength, stiffness and fatigue resistance,” said Brian Baleno, Global Automotive Business Manager for Solvay Speciality Polymers.

In addition to the current cam sprocket application, Holtzberg’s programme will leverage Solvay’s advanced polymer technology to develop up to ten engine parts. These include a water pump, oil pump, water inlet/outlet, throttle body, fuel rail and other high-performance components.