|Federal-Mogul’s DuraBowl technology strengthens the crown of a piston, improving the aluminum’s strength where it is most needed. Click to enlarge.|
Federal-Mogul Corporation has developed an aluminium piston that meets the higher strength and thermal performance demands of very high-power diesel engines. BMW is the first to use the piston in its triple-turbo 3.0-liter diesel (N57D30S1) engine applied in the M550d xDrive, with a specific power output of 93 kW/liter (124 bhp/liter).
The aluminium piston’s design uses the company’s DuraBowl process (earlier post) to create a reinforced combustion bowl rim to withstand the high mechanical and thermal loads. The thermal performance comes from a raised cooling gallery, made possible by Federal-Mogul’s development of a two-dimensional (2D) ultrasonic inspection process.
Federal-Mogul’s DuraBowl process re-melts the alloy around the rim of the piston’s combustion bowl, refining the aluminium’s microstructure and improving the fatigue strength of the material. To ensure control of key parameters, every bowl is tested using the company’s proprietary eddy current process, which detects imperfections below the metal’s surface.
The piston’s raised gallery places the cooling oil as close to the piston bowl as possible to achieve maximum cooling.
The cooler running of the piston enables durability and also reduces internal friction. This technology will play a significant role in enabling OEMs to introduce more efficient downsized diesel engines with improved fuel economy and CO2 emissions.—Arnd Baberg, Chief Engineer Piston Product Engineering, Federal-Mogul
|Federal-Mogul's 2D ultrasonic inspection technique enables high performance pistons for diesel downsizing. Click to enlarge.|
Positioning the oil gallery closer to the piston’s rim and bowl required a major advance in the precision and reliability of the casting process. Federal-Mogul has developed a new 2D ultrasonic inspection technique that has given the company a much deeper understanding of the process and tighter control of quality.
Standard, one-dimensional ultrasonic testing can identify defects but cannot quantify their size and position, said Baberg. The new 2D ultrasonic process provides 125,000 data points in 30 seconds. Using the technique, Federal-Mogul engineers can accurately determine the size and position of defects, providing valuable data for casting process development. The detailed information produced by the non-destructive test also ensures consistent quality in the finished high-precision components, he said.
Federal-Mogul validated the technology by dissecting and sampling hundreds of pistons, correlating the ultrasonic images against destructive testing methods. The research resulted in the development of software tools as well as a number of key physical parameters such as probe geometry, wavelength, beam geometry and focus.
Premium vehicle manufacturers are introducing higher power diesel engines that improve dynamic performance, CO2 emissions and fuel economy, but power outputs of more than 90kW/liter have long challenged piston designs, Federal Mogul notes.
Increasing the specific power output produces higher mechanical loads and temperatures, making a piston’s heat dissipation as important as its strength. Our aluminium piston can operate efficiently under higher thermal and mechanical loads than previously possible, without the risk of engine oil cracking and carbon deposit formation associated with a steel piston. By combining all our process and materials expertise, Federal-Mogul has produced an aluminium piston with the durability and the thermal characteristics that high-power diesels require. These advances mean that aluminium pistons can retain their leading position in diesel engines for light vehicles for some time to come.—Gian Maria Olivetti, Federal-Mogul’s vice president for Technology and Innovation, Powertrain Energy
The piston was developed at Federal-Mogul’s center for aluminium piston development and production in Nuremberg, Germany.