Polymer swirl generator ups turbocharger efficiencies

Design engineers at BMW are seeing improved efficiencies by using swirl generators made from thermoplastic polyester elastomer on certain engine types, to rotate combustion air before it enters the turbocharger compressor. The injection moulded part, co-developed and manufactured by German company Borscheid & Wenig (B&W), is made from DuPont's 'Hytrel', a thermoplastic polyester elastomer. The flexibility offered by this material, along with a pretty clever swirl blade design, means that the position of the swirl generator's four blades automatically and accurately adjust to airflow. This results in a regulated flow of incoming air to the compressor, which is adapted to the revolutions of the turbocharger, therefore improving efficiency and reducing engine sound levels. In their idle position, the blades of the swirl generator are almost at a flat angle to the airflow, resulting in a very effective swirling of the air at low revolutions. With an increase of airflow speed, the surfaces of the blades are stretched backwards, reducing air resistance and therefore the swirl effect. It was this self-adjusting function that won the swirl generator first place in the Power Train section of the SPE Central Europe Automotive Division Awards 2004. The annual award is presented to those products that illustrate particular implementation of polymer expertise in the automotive sector. Developers at BMW selected Hytrel for its high flexibility, good resilience and fatigue strength, even under high temperatures or after long term exposure to aggressive blow-by gases. The grade used for the swirl generator, Hytrel 5555 HS, is an easily-processed, heat stabilized, plasticiser-free grade for injection moulding and extrusion with medium hardness (55 Shore D), good impact resistance at temperatures down to -40°C and a continuous operating temperature of up to 135°C. Michael Fischer, polymer technician at B&W commented: "Thanks to the close cooperation between BMW and DuPont, we were able to complete this development over a very short time. Our responsibility laid in the complete tool design, from receipt of the original CAD models, production of the original moulding tool and its optimisation, to the serial production of the part. We achieved a complex parting line without undercuts, which in turn had a major contribution to the short cycle times achieved."