Plastic parts are increasingly replacing metal in under the hood applications. But, James Snodgrass asks in this feature for Plastics News Europe, will this process go right into the engine itself?
Television petrolhead Jeremy Clarkson once tested the world’s top selling car. Not, as might be expected, a Toyota Corolla or a Ford Focus but a child’s toy made of plastic, the Little Tikes Cozy Coupe, which has sold 22 million units since its release in 1979. The comparison with a child’s toy is one that many will make when the notion of a plastic engine is mooted. While consumers have happily (and possibly unknowingly) accepted plastic substitution in parts as disparate as body panels, bumpers and accelerator pedals, the thought of a fully-plastic engine might prove a harder sell.
But next year could prove to be a decisive moment for the public perception of the all-plastic automotive engine, when the Polimotor 2 takes to the racetrack.
The genesis of the Polimotor 2 goes right back to the 1980s, when American engineer Dr Matthew Holtzberg, developed his first Polimotor engine. Holtzberg’s experiments with plastic started in 1969, when he made a plastic piston for an Austin Mini. But within 20 minutes of operation, the heat of the engine burned through the piston’s crown.
Undeterred, Holtzberg replaced the crowns with aluminium and, in the 1970s, began selling ultralight plastic pistons for use in racing cars. In 1979 he formed the Polimotor company and, in 1980, had his first plastic engine. By 1984 a second-generation Polimotor engine raced successfully in a Lola T616 sports car in the IMSA Camel Light road race series.
“We have proven that this technology works,” Holtzberg told CBS News at the time, “all the Torlon [PAI] engine parts that are in there will run for three hours at 8-9,000 rpm. What we’re trying to show is that this isn’t just a lark.
“I think what we’re trying to do is start what I feel will be a major effort in the automotive industry. We’ve seen the transition from metal to plastic in every other aspect of industry. I think it’s only a matter of time.”
Fast forward in time 30 years to 2016 and the next-generation Polimotor 2 all-plastic automotive engine will take to the racetrack. Belgian materials group Solvay will partner with Holtzberg’s Composite Castings to provide many of the plastics used in the motor.
Automotive engines are the single heaviest part of any car. The aim of the Polimotor 2 project is to develop an engine weighing just 63-67 kg (about 41 kg lighter than a standard production engine).
”The Polimotor project is yet another pioneering opportunity for Solvay Specialty Polymers to bring its innovations to the forefront and to expand its lightweighting offerings,” said Augusto Di Donfrancesco, president of Solvay’s Specialty Polymers Global Business Unit.
Solvay polymers will be used to replace up to 10 of the engine components including the water pump, oil pump, water inlet/outlet, throttle body, fuel rail and cam sprockets. The Solvay polymers used in the Polimotor 2 are Torlon polyamide-imide (PAI), Amodel polyphthalamide (PPA), KetaSpire polyetheretherketone (PEEK), AvaSpire polyaryletherketone (PAEK), Radel polyphenylsulfone (PPSU), Ryton polyphenylene sulfide (PPS) and Tecnoflon VPL fluoroelastomers.
Solvay has yet to announce which polymers will be used for which parts. Brian Baleno, Solvay Specialty Polymers global automotive business manager, told Plastics News Europe: “Solvay will shortly be announcing the material for the cam sprocket and highlighting the benefits of replacing steel. Additionally, Solvay will be announcing the materials for the air intake (plenum), and the oil scavenger line.”
The Polimotor 2 four-cylinder, double-overhead cam (DOHC) engine will be installed in a Norma M-20 concept car in 2016 for competitive racing at Lime Rock Park in the US, where the Polimotor-engined Lola had its most competitive run (third placing) in the 1984-5 season.
The weight saving advantages of using plastics in engines are obvious, but Holtzberg believes it will also reduce manufacturing costs. “Material costs will not be a significant advantage,” said Holtzberg, “but the huge savings in tooling, as a function of tool life for plastics in general, will save an OEM a lot. For example, a typical four-cylinder block tool for die casting aluminium costs $1m and only yields 100,000 blocks. A comparable tool for the plastic block costs $500,000 but will produce five to ten times more blocks.”
The plastic parts for the Polimotor 2 engine will be produced using 3D additive manufacturing, injection moulding and compression moulding. Holtzberg is confident that the expected working life of the plastic components will compare well with their metal counterparts. “They should be identical. There is no reason why not,” he said.