A method for the estimation of the service life of a precision guiding interface "needle - Nozzle Body" of a common-rail-injector for high rail pressures

The analysis of type and form of the loading in the guidance between the needle and body of a CR-injector, as well as the transformation of friction energy on the contact surfaces which absorbs mechanical and thermal loads with deforming and heating the contact layer is presented. The dominant parameters of friction and wear for the investigated interface (radial force, mode of friction, relation for the nominal and real contact areas etc.) are shown in function of different values of rail pressures, varying from 500 to 3000 bar. A special coefficient of accumulation of energy is defined. With these coefficient the analysis of thermal- and stress-conditions for the precision tribosystem become possible. Furthermore this leads to the calculation of the intensity of wear for the mentioned components of the nozzle. The estimation of the service life for the guidance is performed for different values of rail pressures, considering the limit values of wear for the components of the nozzle and of a gap in the contact interface.