Structure and operating algorithms of the system for monitoring of the shaft’s axial dis-placement in combined journal-and-thrust bearing of the turbo-pump unit of liquid-propellant rocket engine NK-33

The problem of early wear diagnostics of the combined journal-and-thrust bearing of the turbo-pump unit of the liquid-propellant rocket engine NK-33 is considered. The main purpose of the diagnostics is to identify the initial stage of the bearings intensive wear. This allows to detect timely the catastrophic destruction of the unit and to prevent the development of emergency destruction of the power plant in general. The significant limitation of the appropriate diagnostic methods was the strict requirements of the inadmissibility of any changes on the number and dimensions of the sensors used in the product body while the existing functions of the turbopump rotor rotation speed monitoring should remain unchanged. The authors proposed a solution based on the replacement of the inductive RPM sensors that are currently used in the turbopump unit parameter monitoring systems with single-coil eddy current sensors with sensitive elements in the form of a conductor segment. This approach made it possible to monitor the axial displacement of the shaft in the combined journal-and-thrust bearing associated with the wear of the assembly and to keep the function of the measuring of the turbopump shaft rotational speed unchanged. The article provides a brief description of the implemented approach to early diagnosis of the condition of the bearing assembly of the NK-33 turbopump unit based on the measurement of the axial displacement of the shaft in the bearing. The technical solutions that implement the approach are based on the use of original single-coil eddy current sensors of a special design with shifted sensing elements, the non-standard converters of their output signals in combination with standard analog-to-digital converters (external modules of the Russian-made L-Card E14-440 ADC) and a PC that provides the control of the data aquisition, processing and visualization. A structural and functional scheme of the control system and its generalized operation algorithm are proposed.