Lubrication and Stress Analyses of the Cam Roller System in a Distributor Fuel Injection Rotary Pump

Design of the pressure pumping mechanism in a distributor fuel injection rotary pump becomes an uneasy task due to the restless demands for raising injection pressure. This paper presents a numerical simulation model developed to analyze the design appropriateness of the cam ring, roller, and shoe components in the pumping mechanism based on their tribological performance. The developed model solves the lubrication of cam/roller and roller/shoe interfaces simultaneously. Lubrication of the cam roller interface is modeled with a mixed lubrication concept to include the surface asperity contact effects. The load-carrying capacity of the surface is characterized by using a contact mechanics model with the measured surface profiles. Assuming the shoe body is rigid, the roller shoe interfacial lubrication is treated as a partial hydrodynamic bearing including the effect at roller slippage. The simulation results indicate that the cam roller film thickness is constantly lower than the surface roughness level. Surface contact stresses are extremely high, since majority of the load is carried by surface asperities. The calculated subsurface stresses indicate that, due to the high surface contact stresses, high stress concentrations are found in the near-surface region within the depth of 10 mm. Hence, the near-surface originated contact fatigue is most likely the dominant failure model for the cam roller interface.