Resumen de Comportamiento de los cojinetes hidrodinamicos en bombas oleohidraulicas de engranajes externos
This PhD work contributes to this global project through the study of the plain journal bearing, or in other words, to comprehend how the shaft of one of the gears moves inside the bearing it has been decided to model the movement of the shaft through the resolution of the differential equations system resulting of the combination of the 2D Reynolds' equation & the solid-fluid equilibrium equations. These last solid-fluid equilibrium equations. These last solid-fluid equilibrium equations have been developed through the Mobility Method (or Lunds' Method). This method has been selected due to the fact that even trough it is a linear method it offers an excellent compromise between precision & complexity; In order to resolve this differential equation system an own finite element program has been developed. This program, which has been named "Motion", taking into account that the lateral compensation plates are static & located in the nominal (geometric centre of the pump), laminar fluid flow and constant viscosity, is able to resolve the above mentioned system in order to calculate them a second own program called "General"has been developed "General" is able to calculate the actions that each has to support versus time if the standard data are given (nº of teeth per gear, assembly distance between gears, manufacturing tool module, ...) as well as the working conditions (working pressure of the pump, r.p.m & temperature). To check the results of the numerical simulation ("Motion") a test bench able to measure the orbits of one of the gear shafts has been develop & build. This measurement is done in a way which allows to determinate the shaft eccentricity & the attitude angle (equilibrium angle) and therefore can be compared with the theorectical study.
Here it has to be highlighted that this kind of measurement is an innovation, not only for the measurement techniques, which have been used, but used, but also for the measurement concept. With the aim of obtaining a wide range of results which will help to understand the behaviour of the pump a DOE (Design of Experiments) has been set up. Therefore 2 different kinds of pumps have been submitted to study. Analysing the spectrums with more detail, it has been observed that in all pumps sub-harmonics of the rotational frequency appear. This sub-harmonics show that the shaft is "floating" or in other words, that the bearings are not rigidly fixed Nevertheless these sub-harmonics have amplitudes which are much smaller than the peaks at the rotational speed, and this means that for a certain defined working conditions, the lateral plate goes to a certain position, and moves around it but not significantly, I. E. like a king of equilibrium.
Going back to the DOE, different behaviours have been identified for different situations.
1. Movement around a fixed working conditions (P, w): a) Pump Type A: The lateral floating compensating plate it is "fixed" & its movement around the equilibrium position can be neglected.
b) Pump Type B: The lateral floating compensating plate "orbits" & its movement around the equilibrium position cannot be neglected.
2. Movement between two different working conditions (P, w): a) Variation of the working pressure: The different positions can be explained through the movement (rotation) of the lateral plate.
b) Variation of the rotational speed (r.p.m.): The movements can be evaluated in all pumps o Pump Type A: the evolution while changing the r.p.m. Is the expected one & predicted by "rotation", i.e. if the rotational speed increases the eccentricity decreases & the attitude angle increases.
o Pump Type B: For the "Test Pump" the evolution while changing the r.p.m. Is not as the expected one but can be explained through the movement of the lateral plate (rotation).
