Increasing endurance of the cross-piece for elastic coupling of crankshaf

Abstract

The article presents the results of an experimental study of the stress state of the body of the crosspiece of an elastic coupling of a crankshaft of a transport diesel engine, establishes the reasons for the violation of the nominal operation of the mechanical connection, gives appropriate recommendations.
Operational tests of the diesel engine revealed insufficient reliability of the elastic coupling. Fatigue was detected in the body of the cross on the surface of the nest for elastic elements located above the scaffolds. The stress state of the cross is due to its pressing on the shank of the crankshaft and transmission through the clutch of dynamic moment.
In the work, the stress from pressing in and from the load by torque is determined and analyzed. It was established that the maximum stresses from pressing appear along the loaded surface in the zone of crack appearance, however, their value of 260 MPa is much less than the maximum temporary endurance of 1100 MPa of the material of the cross (18KH2N4MA steel). Thus, pressing the crosspiece onto the shank of the crankshaft does not lead to a crack. Moment on the crankshafts appeared during injection into the cylinder under high oil pressure. An oil pressure of 15 MPa corresponds to a moment of 100 kNm. Analysis of the results allows us to note that the stresses on the outer surface of the crosspiece reach their maximum in the zone of crack appearance, which corresponds to the loaded edge of the flat. An excess moment equal to the difference between the moment and the moment of rest friction begins to be perceived only by flats, as a result of which the stresses in the crack appearance zone increase sharply.
Various options for the coupling load are analyzed and recommendations are developed for a possible change in the design of the assembly. An increase in the dimensions of the cross in the direction of the longitudinal axis by 10 mm (width) and the length of each flat by 7 mm, eliminated the root causes of the crack, that is, wrinkling and wear are flatter.