Issue: May 2003


Cooled Ring Carrier Design For Direct Injection Diesel Pistons



by Mike Mercer

The high ignition pressures, temperatures and specific output of the latest generation direct-injection diesel engines are creating new challenges for engine component suppliers. Emissions-compliant engines place new demands on components, especially those directly involved with the combustion process such as pistons, in the area of thermal loading.

Mahle Inc. has developed a line of aluminum pistons for high-speed light-, mediumand heavy-duty, direct injection diesel engines that features a cooled ring carrier designed to be highly resistant to the increased temperatures of modern diesel engines.

The Mahle DI diesel piston is designed with a cooled ring carrier cooling duct formed by a steel plate. This sheet metal channel is welded directly to the ring carrier. Oil is circulated through the passage to assist in piston cooling. The design, Mahle says, is a departure from the more common salt core gallery cooled piston which has been used.

The challenge is to design a piston and ring package that will be light, resist high combustion temperatures and pressures, control oil consumption and provide optimum sealing to prevent blow-by, says Joe Strong, director of sales and application engineering for diesel engines at Mahle.

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 material.

One benefit of the welded steel design is the ability to place the cooling gallery closer to the top ring groove for better cooling of the piston crown and the top ring carrier. According to Mahle, comparative finite element calculations on passenger car direct injection diesel pistons with cooled ring carriers and salt core cooling ducts have shown that the cooled ring carrier technology reduces the temperature at the bottom of the first groove by approximately 122 degrees F (50 degrees C).



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