Degradation assessment and life prediction of electro-hydraulic servo valve under erosion wear

This paper presents a degradation assessment and life prediction method for electro-hydraulic servo valve (EHSV). Unlike traditional statistical methods, our work is motivated by the failure mechanism of erosion wear. The degradation of performance characteristic was related with structure wear in twin flapper-nozzle valve and spool valve. Mathematic models of turbulent and erosion wear were established by the combined technologies of computational fluid dynamics and erosion theory. By visual simulation, we analyzed the erosion wear distribution and erosion wear rate under different contaminated oil conditions and working missions. Furthermore, degradation models of performance characteristic were built according to degradation trends of system performance under different erosive wear stages. Finally, the assessment results show that: (1) Hydraulic oil with contaminant particles will distinctly erode the sharp edges of valve bushing and spool. Besides, the erosion rate depends on valve structure and port opening size. (2) Wear at sharp edges of spool valve influences pressure gain, null leakage flow and lap. Furthermore, these performance indicators are monotonically degraded. With the definition of failure for the EHSV, the service life is 9000 missions by our simple mission profile.