ADVANTAGES OF LIGHT-WEIGHT RECIPROCATING PARTS 220044
After pointing out that the general question of weight reduction is no exception to the fallacies that seem to have beset the development of the automobile from its earliest days, the author outlines briefly the problem confronting the automobile designer. The influence of the weight of the reciprocating parts on the chassis in general and the engine in particular is emphasized as being of greater importance than the actual saving in the weight of the parts themselves, it being brought out that the bearing loading due to inertia is really the factor that limits the maximum engine speed. Reference is made to the mathematical investigation by Lanchester in 1907 of the advantages of using materials of high specific-strength and the conclusions arrived at are quoted in full. A tabulation of the specific strengths of various materials used in automotive engineering practice is presented as showing the advantages of aluminum as compared with steel.
The savings in weight that are possible by use of aluminum without any sacrifice of strength are next pointed out. Comparison is made of the stiffness of steel and aluminum sheets as a specific instance of weight reduction and this is followed by an extended consideration of aluminum connecting-rods, including an analysis of the loading due to inertia throughout a complete four-stroke cycle, and a comparison of steel and aluminum connecting-rods on a weight basis. The advantages of using aluminum to secure the required stiffness in a connecting-rod because of its low density are emphasized, it being brought out as the result of a mathematical analysis that equal stiffness as compared with steel can be secured in an aluminum connecting-rod with about one-half the weight of the material. An extended comparison of steel and aluminum connecting-rods that have been in service is next presented. The production methods employed for steel connecting-rods are stated as being applicable to aluminum. The advantages of the combination of the aluminum piston and the connecting-rod are pointed out, it being stated that a saving of 15 lb. in this connection as compared with a cast-iron piston and a steel connecting-rod results in an overall saving of about 14 times this amount.