The BMW Group’s B58 3-litre straight-six petrol engines features an integrated indirect charge air cooler from MAHLE. The system is made from DuPont™ Zytel® PLUS nylon which has particularly good resistance to heat and hot air ageing. The aluminium heat exchanger, through which coolant flows, is inserted lengthwise into the housing on guides which have sealing strips made from the same polymer. The innovative structural design of this charge air cooler means it can be arranged in the immediate vicinity of the engine, so minimising bulk and pressure drop and helping to optimise the balance of performance and fuel efficiency. The BMW Group has been using the B58 engine in its 740i, 440i and 340i models since late 2015.
As Martin Valecka, development project manager at MAHLE, explains: “By deciding on a glass fibre content of 35% by weight, we ensured a good balance of rigidity and impact strength. This combination of properties meant we were able to provide numerous thin-walled but nevertheless highly-effective supporting ribs. These ribs help to minimise deformation of the intake system even at high charge air pressures and temperatures and to ensure durability over the entire service life. Thanks to the very good flowability of Zytel® PLUS, we can achieve short injection moulding cycle times, despite sometimes narrow flow paths for these large volume components. Good flow ability also better supports cost-effective manufacture.”This innovative application has been jointly developed by a team from Mahle, BMW and DuPont Performance Materials who selected the glass fibre reinforced grade Zytel® PLUS 95G35. This choice arouse from the product’s inherent outstanding resistance to chemicals and temperatures of up to 230 °C combined with a very good weldability. For this application, high weldability, using friction welding, is particularly important given the large size of the upper and lower parts of the housing which are moulded in one shot in an injection moulding tool with an 1+1 cavity.
Zytel® PLUS is produced using DuPont’s proprietary SHIELD technology which combines an innovative polymer backbone architecture with specific polymer modifications and additives. Zytel® PLUS 95G35 is the multipurpose product within this product family. Thanks to its very high heat resistance, it retains the majority of its mechanical properties even after 3000 hours at 230 °C, bearing in mind that the properties of conventional PA66-GF35 grades drop to below half their initial value at 180 °C.
"Thanks to the SHIELD technology, components made from Zytel® PLUS which are exposed to hot oil, hot air, coolant and road salt can achieve a service life twice to three times that of parts made from conventional nylons”, says Dr. Olena Novikova, Key Account Manager, DuPont PerformanceMaterials. “This resistance means the material is of interest for applications on the hot side of the air intake as well as for cylinder head covers, resonators, exhaust gas systems and oil sumps. The plastic parts of MAHLE’s integrated indirect charge air cooler can thus easily withstand the specified temperatures of -40°C to 190°C and exposure to blow-by and recirculated exhaust gases over the vehicle’s entire service life.”
Background: integrated indirect charged air cooling Integrating indirect charged air cooling by means of liquid coolants, offers considerable advantages over the conventional approach of directly cooling charged air with outdoor air. It llows to relocate this cooling operation to the immediate vicinity of the engine as opposed to the front end of the vehicle. This results in: :
• Saving Space:
The charged air is cooled close to the engine by a coolant which is in turn cooled by outdoor air in a separate low-temperature circuit. This low-temperature cooler is very compact and so saves front-end space. The bulky charge air hoses used in direct charge air cooling are replaced by thin coolant lines. There is no requirement for ducts between the charged air cooler and intake manifold.
• Boosting Performance:
Due to a smaller volume and short flow paths, the pressure drop is up to 80 % lower than in conventional direct cooling. This translates into a higher volumetric efficiency in the cylinder. In addition, cooler air remains available to the engine for longer time for example under hard acceleration. Both factors have a positive impact on engine performance and responsiveness