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Wheels:
Specialty polymers chosen for plastic engine project

The Polimotor 2 project selected Solvay Specialty Polymer's high-performance Torlon polyamide (PAI) to replace conventional metal in an innovative cam sprocket design for a next-generation, nearly all-plastic racecar engine. (Photo courtesy: Solvay Specialty Polymers)

 

 

 

 

The Polimotor 2 project, led by automotive innovator Matti Holtzberg, has selected Solvay Specialty Polymers' high-performance Torlon polyamide-imide (PAI) to replace conventional metal in the fabrication of an innovative cam sprocket design for a mostly plastic racecar engine.

Holtzberg created and successfully raced a version of the plastic engine concept in the 1980s.

His first-attempt engine in 1980 was described as "a clone of the Ford Pinto 2.3-liter 4-cylinder" in a 2009 New York Times article and "used plastic for the block, piston skirts, connecting rods, oil pan, and most of the cylinder head. Bore surfaces, piston crowns, and combustion-chamber liners were iron or aluminum. The crankshaft and camshaft were standard metal components."

A second-generation effort in the mid 1980s contained 90 percent plastic parts and was run in a racecar in 1984 and 1985.

Solvay is the principal material sponsor for the latest iteration of this highly anticipated technical project, which aims to design and manufacture a next-generation, nearly all-plastic, four-cylinder double-overhead CAM engine that weighs between 138 to 148 lb (63 to 67 kg), or about 90 lb (41 kg) less than today's standard production engine. It includes a carbon-fiber Ford Duratec engine block cast that is about 22 lb (10 kg) lighter than the OE aluminum block.

The target is to use the engine in a French Norma M-20 concept racecar in 2016 to compete at a racing event at Lime Rock Park, CT. According to EngineLabs.com, "The updated Polimotor will sport a turbocharger, improved fuel injection, and a few other modern racing tricks to produce 420 to 450 horsepower at 8,000 rpm."

"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, based in West Palm Beach, FL. "Solvay's continuing advances offer the basis for even greater innovation in Polimotor 2 today, where its carbon-fiber-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."

In addition to the current cam sprocket application, Holtzberg's program will leverage Solvay's advanced polymer technology to develop up to 10 engine parts. These include a water pump, oil pump, water inlet/outlet, throttle body, fuel rail, and other high-performance components. Other Solvay materials targeted for use in the Polimotor 2 project include Amodel polyphthalamide (PPA), KetaSpire polyetheretherketone (PEEK), AvaSpire polyaryletherketone (PAEK), Radel polyphenylsulfone (PPSU), Ryton polyphenylene sulfide (PPS), and Tecnoflon VPL fluoroelastomers.

Allegheny Performance Plastics, a leading processor of high-performance thermoplastics, injection molded the cam sprocket net shape. Gates Corp., a premier manufacturer of power transmission belts and a premier global maker of fluid power products, performed final machining to incorporate a spur tooth design that reduces wear and optimizes transfer of transmission torque between the sprocket and the belt. Ultimately, 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 must reliably 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. However, Polimotor 2 opted to mold 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.

As a class of materials, Solvay's Torlon PAI delivers the highest strength, stiffness, and fatigue resistance of any thermoplastic technology up to 525 deg F (275 deg C). Torlon 7130 PAI, in particular, delivers the portfolio's most optimal balance of these mechanical properties, with a specific strength of 5.4 x 10⁵ in.-lbf/lb (1.4 10⁵ J/kg) and specific stiffness 6 x 10⁷ in.-lbf/lb (15 10⁶ J/kg). Stainless steel, in contrast, delivers specific strength and stiffness of 3.1 x 10⁷ in.-lbf/lb (0.8 106 J/kg), and 9.7 x 10⁷ in.-lbf/lb (24 10⁶ J/kg), respectively.

In practical terms, 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 2.4 lb (1.1 kg).

The Polimotor 2 plastic engine will power a French Norma M-20 concept racecar in 2016.

 

 

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.

"The selection of high-strength, lightweight, fatigue-resistant Torlon PAI over traditional sintered steel or aluminum was critical to our ability to develop a new, state-of-the art valve train drive system for Polimotor 2," said Fraser Lacy, senior engineering specialist for Gates Corp.

Torlon PAI and other Solvay high-performance polymers are seeing strong adoption as a metal replacement option in automotive engines as OEMs move to downsize and downspeed them. Solvay's advanced polymers offer higher efficiency through reduction of weight to enable OEMs to comply with tougher corporate average fuel economy (CAFE) regulations and stricter CO₂ emission standards, both of which are considered top priorities for the automotive industry over the next decade.

"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 Specialty Polymers. "One notable area is metal replacement for needle bearings, where Torlon PAI saves both weight and space, allowing transmissions to be smaller than comparable aluminum castings, which helps reduce CO2 emissions and lower cost."

3D printing will be part of the creative process too
The Polimotor 2 engine will also feature a 3D-printed plenum chamber fabricated through selective laser sintering (SLS). The plenum will be made of a Sinterline Technyl polyamide 6 (PA6) powder grade reinforced with a 40 percent loading of glass beads to enhance dimensional stability.

An automotive plenum is the pressurized chamber that uniformly distributes the air flow between an engine's inlet and cylinders. The plenum in the Polimotor 2 engine will share similar specifications to those in today's production-scale automobiles, which are typically injection-molded nylon with 2-mm to 3-mm wall thickness to withstand the 2 to 4 bars of positive air pressure inside.

Based on the same resin chemistry as Solvay's proven Technyl polyamides, Sinterline PA6 powders are formulated to leverage the benefits of 3D printing for nylon components. Laser sintering and other 3D-printing processes improve productivity by quickly converting digital designs into functional parts without the time or cost required to first build a molding tool and prototype. Thus, they can significantly accelerate the time-to-market for OEMs and Tiers.

Laser sintering applies the energy from a high-precision laser scanner to fuse Sinterline Technyl PA6 powders, layer by layer, until they form a finished, highly functional three-dimensional part with enhanced mechanical and thermal properties. Because parts are printed in successive layers, laser sintering can also quickly produce components that integrate complex internal features and functions.

Parts printed from Sinterline Technyl PA6 powders are capable of performing reliably in a conventional metal turbocharged engine, where radiant temperatures can reach as high as 250 deg F (121 deg C). Notably, however, the plenum in the Polimotor 2 concept will encounter comparably lower temperatures between 150 deg F (66 deg C) and 200 deg F (93 deg C), due to the low thermal conductivity of the engine's largely plastic composition.

Engine Labs has a more detailed article on the Polimotor 2 project. Read it here.

Source: Solvay

Published December 2015

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