Designed for use in smaller engines, Continental’s new turbocharger featuring an industry-first aluminum turbine housing enters production on BMW’s 1.5 L three-cylinder, 134 hp (100 kW) B38-series engine that powers the 2014 Mini Hatch.
“We have been developing this over the last two years with the BMW group,” revealed Kregg Wiggins, Senior Vice President Powertrain Division, Continental North America. “This type of technology would not have been available within the last few years because of the difficulty of matching the thermodynamics and system expertise needed to bring it to market.”
Speaking with Automotive Engineering and other media at the 2014 Management Briefing Seminar in Traverse City, MI, Wiggins provided technical details of the new boosting device beyond those recently reported (http://articles.sae.org/13363/). The turbocharger is a radial-axial, single scroll design. “Using cast aluminum as a replacement for the typical specialty cast steel alloys used equals a more cost-effective unit, even with the addition of a cooling jacket,” he said.
Performance was important as well. “We wanted to reduce the transient time as much as possible, so we have some innovative methodologies to reduce transient time [for spooling up the turbine],” Wiggins explained.
He also noted that the aluminum, water-cooled design “is most appropriate for smaller engines.” That is consistent with Ducker Research forecasts, which show water-cooled turbocharger systems (and additional aluminum content) growing in the 2020 to 2025 time period, but limited to small displacement engine applications.
Turbocharger turbine housings must endure exhaust gas temperatures ranging from 400-1050°C and high thermal stresses up to 140 MPa (20,300 psi) around the wastegate seat and center divider areas, experts note. Until Continental’s innovation, the housings typically have been cast in ferrous alloys such as Ni-Resist D2B, HK30, and cast austenitic stainless steel, which feature high nickel and silicon content for excellent heat resistance. Compressor housings typically are aluminum castings, and bearing housings are cast iron.
In developing their new turbo machine, Continental engineers saw opportunities to reduce cost and weight by designing a water-cooled turbine housing in cast aluminum. (Continental would not divulge the specific alloy employed on the initial BMW application.) Continental’s patent application, “Turbocharger with Cooled Turbine Housing” published December 2013 states that the high-pressure-resistant nickel alloys “represent a considerable cost factor” and those high material costs make a ferrous-alloy turbine housing “the most expensive single item in the overall costs of an exhaust-gas turbocharger.”
More than the aluminum makes this turbocharger special. Instead of a typical bolt-on component, it is an integral part of the engine. The concept of cooling the turbine housing via an internal jacket using water from the engine’s normal coolant circuit “was born from a system optimization between us and BMW Group,” Wiggins said. “They wanted to try and see from an overall system perspective if we could develop a more cost-effective package.”
At the same time, keeping design options open was important. Continental turbochargers with a steel-alloy turbine housing can also be attached to the same base engine using the same interface on the cylinder head. This option is for high-performance engines or vehicles for export to high-temperature countries, according to Continental. The bearing housing on steel variants is cooled from inside, while aluminum housings are cooled from the outside.
This is the second entry for Continental into the exhaust turbocharger market. Why enter a market with long established, existing players such as Honeywell or BorgWarner? “The automakers were looking for competition,” Wiggins replied. “We expect the gasoline turbocharger market to grow by 13%,” he said. “The growth of the market is such that it can support new players.”
In that sense, Continental joins Bosch Mahle Turbo Systems, the joint venture between Robert Bosch and Mahle that also started producing gasoline turbochargers in 2013.
The water-cooled, aluminum turbine housings are cast by a large German-based aluminum company. The turbochargers are manufactured currently in plants in the Czech Republic and Germany, with two new plants coming on-line in 2017 in North America and China, according to Wiggins.
Senior Editor Lindsay Brooke contributed to this article.