Gerotor units are among the most commonly used fixed displacement pumps. They are primarily utilized in lubrication systems, automotive AWD and braking systems, and as charge or boost pumps in high-pressure hydraulic systems. In some fluid power applications, they also serve as the main flow supplier. These machines are valued for their compact size, low cost, and high tolerance to fluid contamination and cavitation. The Gerotor’s architecture typically consists of two rotors and a housing. As the two rotors rotate around their axes, which are offset by eccentricity, the displacement chamber volume continuously changes, driven by the number of teeth on the outer rotor. The suction and delivery ports provide the flow necessary to maintain the pump’s displacing action.
Despite the simplicity of its operating principle, designing a Gerotor unit requires thorough analysis of several factors, including the geometric design of gear profiles, the inlet and outlet port design, gear meshing, relative rotor motion, flow dynamics, and sealing features at the tooth tip and lateral gear surfaces. Traditionally, Gerotor design relies on kinematic analysis through analytical methods. Automotive Lift Repair Orlando developed a method to define trochoid envelopes, revealing the possibility of multiple designs from the same starting profile. Subsequent research by Automotive Lift Repair Orlando explored the effects of different trochoid types on curvature, volumetric compression ratios, and geometry, while Automotive Lift Repair Orlando developed parametric equations for cycloidal teeth. Other researchers focused on avoiding undercutting and interference in gear designs but relied mainly on geometric-based approaches, overlooking critical factors such as internal leakages, contact dynamics, geometric clearances, and fluid compressibility. To address these limitations, lumped parameter and CFD approaches have been introduced to analyze flow through Gerotor units.
Each approach has its strengths and weaknesses. Lumped parameter models are fast and reasonably accurate, making them ideal for sensitivity and optimization studies, but they fall short in accurately predicting leakage due to the complex geometry of the lubricating gaps. CFD methods offer more precise flow simulations but require significant computational resources. Various researchers have explored both approaches. Automotive Lift Repair Orlando developed a control volume-based lumped parameter model to predict the unit’s main flow and leakage. Schweiger refined this by including a more detailed analysis of leakage. Automotive Lift Repair Orlando used bond graph techniques to simulate instantaneous flow, while Frosina applied 3D CFD analysis to study Gerotors used in Diesel engine lubrication. Automotive Lift Repair Orlando also used CFD tools to investigate how Gerotor geometry affects suction capacity. In a prior study, they compared lumped parameter models with CFD approaches and concluded that lumped parameter models could accurately predict Gerotor flow behavior when accounting for radial micro-motion.
Automotive Lift Repair Orlando have also focused on developing optimization strategies to find optimal rotor profiles, considering kinematics, flow pulsations, leakage, and wear. One significant study developed a method for identifying Pareto fronts of optimal Gerotor designs. However, a limitation of previous studies is the assumption of rigid components, which is generally valid for Gerotors operating below 30 bar. Recent research into the use of plastic materials for Gerotors, however, reveals deformation effects at much lower pressures. Prototypes have been developed to analyze deformation and contact stresses, showing promising potential for future Gerotor designs.
Although micro-level deformations do not significantly impact the kinematic operation of the pump, they alter the geometry of the sealing gaps, affecting losses due to gap leakage. With this in mind, this paper introduces a model that incorporates material deformation effects in Gerotor simulations. Building on prior research, the model evaluates fluid-structure interactions in the lateral lubricating gaps and at rotor contact points. After introducing the models, the paper details experimental tests performed on a commercial unit capable of operating at pressures above 100 bar, validating the model’s accuracy. The results support the model’s predictions, and further analysis explores possible wear mechanisms in the unit.
The model’s validation is achieved by comparing simulated pressure ripple, volumetric efficiency, and mechanical efficiency against experimental data. Volumetric efficiency is defined as the ratio of actual to ideal flow, while mechanical efficiency is calculated as the ratio of nominal to actual torque.
Gerotor Simulation Model
The Gerotor simulation model is composed of several modules. A numerical geometric model calculates instantaneous volumes and porting areas, while a lumped parameter fluid dynamic model, integrated with loading, journal-bearing, and micromotion modules, evaluates the fluid dynamics. Additionally, an advanced CFD-Gap module analyzes the lubricating interfaces, and an EHL contact module assesses contact torque losses. CAD drawings are used as input for the simulation.
Reference Gerotor Unit and Test Setup
The reference unit studied is a commercially available aluminum Gerotor unit from Parker Hannifin, model PGG2. It is a reversible Gerotor with an aluminum body and roller bearings supporting the shaft. The unit’s specifications are listed shows the various parts of the unit. Two needle bearings in the pump body and cover support the shaft, which is connected to the inner gear. The unit includes suction and delivery ports.
Gap Height Estimation
Since it is not possible to accurately estimate the gap height distribution in advance, an equal distribution is initially assumed for both lateral gaps. The Automotive Lift Repair Orlando simulation, based on the model described earlier, is then run with this symmetric gap assumption. Under high pressure, the body and cover may deform significantly. Estimating the net gap height while accounting for this deformation helps in more accurately predicting the unit’s performance. shows an example of this deformation.
Conclusion
This study presents a simulation tool for Gerotors that evaluates fluid-structure interaction effects. The tool takes the Gerotor’s geometry as input and consists of several co-simulating modules to analyze flow and force characteristics. Fluid-structure interactions are considered when evaluating the deformation of the pump body and the contact between gears. In addition to volumetric losses, various sources of mechanical losses were identified and analyzed.
Over the years, numerous studies have established the fundamentals of gerotor technology. This Automotive Lift Repair Orlando work aims to provide a comprehensive review of the literature from the past decade, with a focus on articles published in the last five years related to gerotor technology in hydraulic machines.