MAHLE GmbH began its development of the Cooled Ring Carrier for Aluminum Diesel Pistons with its first patent in 1956. While production projects did not materialize, the design and processing continued to be developed until further patents were established in 1970 and 1972. These designs were further refined to what we have today.

MAHLE is prepared to offer this technology, not only from Europe, but also from MAHLE North America and South America as customer interest develops. Current production projects include three European engines with volumes exceeding one million units. For additional committed high-speed automotive diesel applications, plans are to increase production to nearly two million units during the next two years.

In addition, development projects are under way for applications in heavy-duty pistons for start of production in 2004.

The production of the Cooled Ring Carrier Ni Resist insert is accomplished by pressing a formed sheet metal channel onto the interior of the normal Ni Resist ring. This is welded in place, first on one side, and then on the other by the use of MAHLE designed welding machines. From here, the parts are leak tested and shipped to a casting facility.

The production of the Cooled Ring Carrier piston presents many challenges and has seen a lot of optimization from the early high costs of production. When the Cooled Ring Carrier design feature is combined with the other design enhancements such as profiled pin bores, stepped connecting rod, and pin bore bushings, even higher peak cylinder pressures can be achieved.

With the Cooled Ring Carrier reducing temperatures at the bowl rim, higher peak cylinder pressures can be similarly achieved with this design beyond what is achievable today with a Gallery Cooled Piston.

A reduction in bowl rim temperature of 10°C can lead to a 100 percent increase in the relative life time prediction for the bowl rim. Bowl rim temperature reductions up to 30°C have been achieved in certain designs. Beyond the primary benefit of reducing bowl rim temperature, the Cooled Ring Carrier design allows a reduction in the top land and ring groove temperatures. Ring sticking and ring wear are positively impacted by these temperature reductions. In some designs where the combustion process requires an offset bowl, the Cooled Ring Carrier may not be an option. A minimum thickness between the combustion bowl and interior diameter of the Cooled Ring Carrier should be considered.

In summary, the Cooled Ring Carrier design allows the designer to go to a higher peak cylinder operating pressure while at the same time achieving the following:

• Increased piston life


• Improved cooling in the area of the combustion bowl and ring grooves


• Moves the salt core out of the high stressed area which has lead to fatigue cracks in some designs


• Changeover from a keystone to a rectangular top ring in passenger car applications


• Reduced amount of lube oil consumption and blow-by

 The MAHLE Cooled Ring Carrier piston design should be considered when these technical challenges can not be overcome with the spray cooled aluminum piston.