Numerical and Experimental Evaluations on the behaviour of Variable Displacement oil pump journal bearings

Matteo Gasperini, Maurizio Moriglia, Raffaele Squarcini
Pierburg Pump Technology Italy

Variable displacement oil pumps produced from Pierburg Pump Technology Italy Spa (PPT) for OEMs usually use two journal bearings in a total of two main layouts regards to pumping element disposition in the overall oil pump. The typical working condition of both bearings in the most stressing conditions is Elastohydrodynamic Lubrication (EHL) regime; due to the complexity of the EHL approach calculation and of the “dynamic wear model”, a commercial code (AVL Excite Power Unit from AVL company) has been used to analyse. A template journal bearing (simmetrically loaded bearing) under known loading conditions has been realized to run a first investigation on a simplified problem in controlled conditions for bearing speed and load (two load cells were used). With the AVL code, estimation of accumulated wear over time has been performed with the Archard model using the corrected Reynolds equation with flow factors proposed by Patir and Cheng and the model of roughness asperity contact proposed by Greenwood – Williamson. Results were compared with experimental measurements by means of a 3D roughness-meter making full scan of the circular bearing seat and shaft surface. Encouraging agreement has been found on wear thickness prediction at both ends of bearings. Concerning the value of constant of wear K, the results of measurements done in some pin-on-disk tests have been used. Moreover, it has been finally demonstrated that an hydrodynamic model to design and check journal bearings in oil pumps is definitely not enough. In the end, after the validation loop on the template bearing, the AVL code has been used to predict performances of two real applications of journal bearings on variable vane pumps already in production.