In the crash tests performed in 1960-61 by Automotive Safety Research Project in the Mechanical Engineering Department of the University of Minnesota, the test data for the forces on a human being held by a seat belt was based upon the effectiveness of the hydraulic shock-absorbing bumper, a 50-cycle per second natural frequency seat belt and a seat belt tightener without release. The present paper presents an analytical study of the same system with the seat belt tightener connected directly to the hydraulic bumper; the tightener cylinder being thus loaded and unloaded with the bumper. Under this system, a seat-belt force is held to ¼ the force otherwise produced on a seat belt without a bumper and retraction. This condition was suggested on page 82 in the original paper, “Reduction in Crash Forces, ” James J. Ryan, Chapter 5, Proceedings of the Fifth Stapp Automotive Crash and Field Demonstration Conference, University of Minnesota, September 14-16, 1961, pp. 48-89, but the means was not determined. Work on an analog computer, as described here, has shown the direct connection of the seat-belt tightener and the hydraulic bumper will perform this function effectively.
