A newly-developed two-component air duct, from system supplier MAHLE of Stuttgart, Germany, connects the intercooler and throttle body of the three liter, six cylinder twin-turbo engine from BMW.
Blow-molded using stiff yet elastic DuPont™ Hytrel® TPC/ET thermoplastic polyester elastomer, the air duct fulfills its task in a particularly efficient manner due to the very low material usage of the design and despite the high pressures and flow velocity encountered in such a high-performance petrol engine.
By reducing the part to just two basic components, the time required for production and assembly is significantly reduced compared to the previous version, which consisted of a series of pipes and clamps. Moreover, blow-molding technology enables greater flexibility in the integration of application-specific connections, such as those required for resonators, sensors or the discharge of gases. Together, the combination of lower weight, more efficient production and assembly, and the integration of variable functionality, provides for a significant cost advantage over the earlier model, which was produced using glass-fiber reinforced nylon and elastomers.
Used on the ‘cold’ side of the engine, the innovative air duct, consisting of two Dupont™ Hytrel® TPC/ET sections measuring 300 mm and 400 mm respectively, is one of the first mono-material solutions of its kind in Germany.
“Despite the ambitious nature of this development, we succeeded, with DuPont’s support, in combining high functionality with high cost-efficiency,” said Thorsten Riechelmann, project manager at MAHLE.
“For example, finite element calculations conducted by DuPont Performance Polymers (DuPont) helped us to optimize wall thickness in line with the given pressure and temperature conditions (2 bar absolute pressure at -40 °C to +100 °C). The same simulations from DuPont also generated very precise assembly data. This enabled us, for example, to optimize the integrated bellows at a sufficiently early stage to ensure that the high levels of deformation, necessary due to the limited assembly space, and the pressure levels required to install it, were within an acceptable range,” said Riechelman. “Overall there was a strong correlation between the values provided by DuPont and those which resulted from actual component testing. We also appreciated greatly the technical support available from DuPont’s technical centre in Geneva with regard to three-dimensional blow molding. From there we were able to source valuable advice on how to conduct both energy-saving and reliable processing, which simplified the start of serial production considerably.”
DuPont™ Hytrel® thermoplastic polyester elastomers from DuPont provide the flexibility of rubbers, the strength of plastics, and the processibility of thermoplastics. This grade of Hytrel® is a specially-modified grade for use in blow-molding, with an increased melt viscosity, a hardness of 55 Shore D and a relatively high stiffness of 170 MPa at 23 °C and 60 MPa at 100 °C. Thus it combines good mechanical properties at high temperatures – a prerequisite for air ducts which are located under the hood and consistently exposed to internal pressure – with high elasticity across a broad temperature range. As with all Hytrel® grades, this blow-molding grade offers long-term resistance to hydrocarbons and other media typical for the automotive sector.