innovations CASTING
Precision Sand Boosts GM Ecotec Engine Performance
F
or its 2.4-L direct injection Ecotec engine released in 2010, Gen- eral Motors wanted to improve fuel economy
and power and reduce noise, vibra- tion and harshness. T e automotive manufacturer determined the preci- sion sand casting process could enable the design changes necessary to make the improvements. In precision sand casting, numer-
ous chemically bonded sand cores are assembled in a fl askless core package to produce the internal passages and external geometries of castings without the use of a traditional mold or pattern plate. T e process achieves tight toler- ances and enabled GM engineers to design features into the part to handle increased engine loads and improve oil fl ow through the engine with refi ne- ments to the oil distribution system. A major requirement for the new Ecotec 2.4-L L4 engine was the ability to work seamlessly with existing block machining opera-
tions in GM engine plants that handle lost foam blocks. T e fi nal design included:
• Ten as-cast oil feed holes from the main oil passage to each crank- shaft bearing surface. Each hole was designed with an arc on one end to enable core assembly in the sand package.
• Four as-cast oil feed holes from the main oil passage to both balance shaft bearing surfaces, which elimi- nated drilling the openings from outside the block.
• Cast-in crankcase ventilation pas- sages and oil return passages.
• Four as-cast oil passages for the oil fi lter, varying in shape and size to enable packaging. T e sand
• Two as-cast main oil passages feeding high pressure oil to the balance shaft bearings, crankshaft bearings and cylinder head, which duplicate the lost foam design and avoid the addition of two long drilling operations.
• Chills in the main bearing bulkhead of the precision sand cast block provided a casting with more than double the fatigue strength than its lost foam counterpart, making it suitable for higher load product applications.
cast block core design avoided four drilling operations and decreased the resistance of oil fl ow from the engine oil pump to the main oil gal- lery lines, improving engine lubrica- tion and oil pump performance.
• An integral chain case, identical to the lost foam block, which allowed for more robust sealing of the en- gine assembly. T e precision sand cast block, which
was provided by Nemak, Nuevo Leon, Mexico, showed a minimal weight increase (2.2 lbs.) over the lost foam block. T e fi rst vehicle applications of the Ecotec 2.4-L L4 engine included the 2010 Chevrolet Equinox and 2010 GMC Terrain, both of which featured best-in-class highway fuel economies of 32 mpg.
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www.gm.com for more information.
The GM precision sand cast engine block was required to incorporate new features for improved performance while fi tting within fi nishing operations established for its lost foam counterpart.
Jan/Feb 2012 | METAL CASTING DESIGN & PURCHASING | 49
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