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Abstract
This article presents a novel fluid structure interaction (FSI) model for lateral lubricating interfaces in an asymmetrically balanced external gear pump. Due to the asymmetry in the geometry of the floating lateral bushes responsible for sealing the displacement chambers in such machines, the lubricating interfaces on either side of the gears have been modeled as distinct but coupled lubricating films. An elastohydrodynamic (EHD) lubrication regime was modeled in all simulations and film thickness predictions for both lubricating interfaces have been achieved. The novel FSI model for the asymmetric lateral gaps is then used in an automatic optimization procedure to design the optimal axial balance in the reference external gear machine (EGM). The optimal axial balance is achieved by determining the optimal balance area on the lateral bush by considering specific design variables associated with it. The procedure aims to find the best feasible design solution that minimizes the total power losses in the lubricating interfaces while also minimizing the nonuniformities in the orientation of these gaps between two significant operating conditions of the EGM. The developed procedure highlights the potential to virtually design the axial balance in EGMs—which represent a key design aspect of pressure compensated EGM—by using an advanced FSI-EHD model.
Nomenclature
| A | = | Area (m2) |
| d | = | Wheelbase of the pump (m) |
| F | = | Force (N) |
| h | = | Film thickness (m) |
| M | = | Moment (N-m) |
| O | = | Order of magnitude |
| P | = | Power loss (Nm/s) |
| p | = | Pressure (Pa) |
| Q | = | Volumetric flow rate (m3) |
| R | = | Outer radius of gears (m) |
| T | = | Torque (Nm) |
| v | = | Cartesian velocity vector (m/s) |
| X | = | Cartesian X coordinate |
| Y | = | Cartesian Y coordinate |
| λ, ξ | = | Lame's coefficients |
| μ | = | Kinematic viscosity of working fluid (Pa-s) |
| ρ | = | Density (kg/m3) |
| τzx | = | Shear stress in XY plane in the X direction (N/m2) |
| ω | = | Angular velocity (rad/s) |
Subscripts
| avg | = | Average |
| Blk | = | Bearing block |
| b | = | Bottom surface |
| Dn | = | Driven gear |
| Dr | = | Driver gear |
| = | Losses due to leakages | |
| = | Losses due to fluid shear | |
| max | = | Maximum |
| min | = | Minimum |
| Pis | = | Balance piston |
| Ref | = | Reference |
| Res | = | Resultant |
| t | = | Top surface |
| UD | = | Undeformed |