Gerotor Lubricating Oil Pump for IC Engines

This paper documents an extensive study aimed at a better understanding of the peculiarities and performance of crankshaft mounted gerotor pumps for IC engines lubrication. At different extents, the modelling, simulation and testing of a specific unit are all considered. More emphasis, at the modelling phase, is dedicated to the physical and mathematical description of the flow losses mechanisms; the often intricate aspects of kinematics being deliberately left aside. The pressure relief valve is analysed at a considerable extent as is the modelling of the working fluid, a typically aerated subsystem in such applications. Simulation is grounded on AMESim, a relatively novel tool in the fluid power domain, that proves effective and compliant with user deeds and objectives. Testing, at steady-state conditions, forms the basis for the progressive tuning of the simulation model and provides significant insight into this type of volumetric pump. INTRODUCTION The reduction of development time of new IC engines prototypes is a key issue in providing automotive industries with enhanced competitive strength. To reach this goal a need exists for the assessment of accurate design approaches that will significantly and beneficially impact subsequent testing. Simulation is certainly a major benefit in achieving optimal performance in systems and components being designed. It is the purpose of this paper, in view of the simulation of the complete IC engine lubrication system, to provide an effective mathematical prediction of gerotor lubricating oil pumps. Basically, the unit consists of a pair of gear shaped elements mated so that each tooth of the inner gear is always in sliding contact with the outer gear to form sealed pockets of fluid. Both gears rotate in the same direction at low relative speeds with the inner gear being slightly faster. Fluid enters the chamber with increasing volume, is trapped in the spaces between the teeth and is transported to the outlet. A schematic of the pump core is shown in Fig. 1. The equivalent hydraulic circuit is presented in Fig. 2. Oil is taken in from the tank (oil sump), passes through the inlet duct and is filtered (strainer F1). Delivered flow is further filtered in F2, and, pending on pressure level, excess flow is recirculated to inlet through a pressure limiting valve VL. Downstream of junction G4, port P connects pump delivery to lubricating oil consumers (U). Figure 1: Pump core schematic Figure 2: Equivalent hydraulic circuit