Effects of Shot Peening on Fatigue Reliability of Valve Spring

According to the service environment and structure features of an engine valve spring, the high frequency spring fatigue test system was designed. The fatigue tests were carried out for the engine valve springs with shot peening and without shot peening, and the relaxation rates of spring were tested at the valve fully open and pre-compression under the condition of different cycle times. The results showed that shot peening could increase the relaxation rates of spring, which were 68.1% and 23.9% at the valve fully open and pre-compression, respectively. After shot peening the relaxation rates of spring were increased by 69.8% and 34.2% respectively under the condition of 99% degree by the means of statistic analysis. And the reasons that no corresponding relation of the relaxation rate of spring in a cycle were analyzed.