Lafayette, IN--For diesel engines, few problems are more insidiously damaging than air leakage. Air leakage can ruin performance, boost exhaust temperatures, and raise emissions. Ultimately, it can even lead to engine failure.
Now, however, engineers at Caterpillar Inc.'s Large Engine Center have developed a way to reduce air leakage through a diesel's aftercooler system. In the process, the new design dramatically simplifies assembly, improves reliability, and cuts engine downtime.
Engineers say the key to reducing aftercooler air leakage is a new mounting and sealing system. Designed for Caterpillar's turbocharged 3500 Series B diesel engine, the new mounting system dramatically reduces the number of bolted connections required, eliminates the need for conventional gaskets, and structurally isolates the aftercooler core. By doing so, it heads off potential problems caused by differential expansion of materials in the system.
The new mounting systems works in conjunction with a "unitized" configuration developed for the aftercooler and air inlet system in the late 1980s. Consisting of three separate parts, the unitized construction system was developed to improve air flow characteristics. But the three parts--a discharge manifold, heat exchanger core, and inlet manifold--required more than 100 bolted connections on some engine models. In some cases, the bolts loosened, causing gaskets to fail and air to leak out.
By employing elastomeric seals and steel "load stops" between the three major components, the new design solves that problem. Developed by Caterpillar project engineer Allyn P. Bock, the system is so designed that the seals provide no load bearing capacity; instead, loads are transferred through the load stops.
* Internal combustion engines
Because they free the system's seals from load-bearing functions, the load
stops are critical to the design. To take loads off the seals, Bock extended the
core walls, forming a small enclosure around the top and bottom of the core.
Elastomeric seals are then pressed into place on the upper and lower enclosures.
Subsequently, the elastomeric seals fit into recesses in the discharge manifold
and air inlet manifold.
Replacing conventional gastets with elastomeric seals allows Bock to dramatically reduce the need for bolted connections. In the past, dozens of bolts were used to compress conventional gaskets. But the elastomeric seal does not need such high compression forces. On most models of the Caterpillar 3500 diesel engine, only twelve bolts are used--and most of those are employed for structural rigidity.
More important, changes in temperature and differing rates of thermal expansion do not affect the new design. That's critical because discharge air is often as hot as 385F, while the heat exchanger core can be as cool as 90F. "With this design, the core can expand and contract at whatever rate it wants because it can grow into the rubber seals," Bock says. "And the covers are free to do the same."
This immunity to temperature changes is particularly important for Caterpillar's Series 3500B engines, because the company uses differing materials for the aftercoolers, depending upon the application.
The resulting air inlet and aftercooler system reduces the fastener requirement from 104 bolts to 12, thus simplifying assembly. By retaining the unitized construction, it maintains the serviceability and air flow characteristics of earlier models. Most of all, however, the system eliminates the problems associated with conventional jointed construction. Says Bock: "Air leakage and the consequent downtime required for repair have been eliminated."
Additional details...Contact Carolyn R. Smyth, Public Affairs Manager, Caterpillar Inc., 3701 State Rd. 26 E., Lafayette, IN 47905.