Effects on Rate Due to End Turns in Automotive Suspension
Traditional approaches in designing helical compression springs include references to “active” and “inactive” turns in a coil. “Active” turns in a coil are those which contribute to the rate of the coil, while “inactive” turns are considered “dead” - those turns which do not contribute to the coil's rate. In the 1930's and 1940's much experimental work had been done to provide guidelines for determining the number of “active” turns for cylindrical springs with various end configurations.
Since the time of that research, new and complex automotive suspension coil spring shapes have been developed. As a result, many of the empirical rules generated for cylindrical springs are not directly applicable. An empirical approach to quantify end turn effects for various spring shapes and end configurations would be quite cumbersome. Even if data were available, spring designers would have to know a large number of rules and apply them properly. In order to simplify the design process and quantify the effects on rate due to end turns, a generalized analytical approach has been developed.