An experimental engine with a lightweight cylinder casing has been developed by the Fraunhofer project group for new drive systems (NAS), which forms part of the Fraunhofer Institute for Chemical Technology (ICT, Pfinztal, Germany), in collaboration with SBHPP, the plastics business unit of Sumitomo Bakelite Co. (Tokyo, Japan).
“We used a fiber-reinforced composite material to build a cylinder casing for a one-cylinder research engine,” said Lars-Fredrik Berg, the project leader and manager of lightweight powertrain design at the Fraunhofer Project Group for new drive systems. “The cylinder casing weighs around 20 percent less than the equivalent aluminum component, and costs the same.”
Berg said that the group first looked at the engine design and identified the areas subject to high thermal and mechanical loads and used metal inserts to strengthen their wear resistance. One example is the cylinder liner, which the piston moves up and down millions of times during the life of the vehicle. The researchers modified the geometry of these parts to ensure that the plastic is exposed to as little heat as possible.
Glass-fiber-reinforced phenolic resin
The characteristics of the plastic material also play an important role. It needs to be sufficiently hard and rigid, and resistant to oil, gasoline and glycol in the cooling water. It must also demonstrate good adherence to the metal inserts and not have a higher thermal expansion coefficient than the metal – otherwise the inserts would separate from the substrate. Berg’s team uses a glass-fiber-reinforced phenolic composite developed by SBHPP, which fulfills all of these requirements and comprises 55% fibers and 45% resin.
The researchers produce these components from granulated thermoset plastics via injection molding. The melted composite material, in which the glass fibers are already mixed with the resin, hardens in the mold into which it was injected. The scientists analyzed the process using computer simulations to determine the best method of injecting the material in order to optimize the performance of the finished product. The process is compatible with mass production scenarios and the manufacturing costs are significantly lower than those for aluminum engine parts, the group stated.
A prototype of this engine is currently being presented at this year’s Hannover Messe, which takes place April 13-17 (exhibit in Hall 2, Booth C16). Test runs of the new engine have been completed successfully.
“We have proved that it is capable of the same performance as conventionally built engines,” Berg says. Initial data also indicates that the amount of heat radiated to the environment is lower than that generated by aluminum-based engines. The scientists intend to take their research further by developing a multi-cylinder plastics-based engine, including the crankshaft bearings.