|  |
| Titel:
|
Feasibility of Applying Controllable Lubrication Techniques to Reciprocating Machines |
| Type:
|
Ph.d. thesisPh.d. thesis |
| Person(er):
|
Forfatter:
Pulido, Edgar Estupinan
Technical University of Denmark
Technical University of Denmark
Email:
|
| Uddrag:
|
The use of active lubrication in journal bearings helps to enhance the thin fluid films by increasing the fluid film thickness and consequently reducing viscous friction losses and vibrations. One refers to active lubrication when conventional hydrodynamic lubrication is combined with dynamically modified hydrostatic lubrication. In this case, the hydrostatic lubrication is modified by injecting oil
at controllable pressures, through orifices circumferentially located around the bearing surface.
In order to study the performance of journal bearings of reciprocating machines, operating under conventional lubrication conditions, a mathematical model of a reciprocating mechanism connected to a rigid / flexible rotor via thin fluid films was developed. The mathematical model involves the use of multibody dynamics theory for the modelling of the reciprocating mechanism (rigid bodies),
finite elements method for the modelling of the flexible rotor (crankshaft) and hydrodynamic fluid film theory for describing the dynamics of the thin fluid films. When active lubrication is introduced to modify conventional hydrodynamic lubrication, by means of aplying radial oil injection at controllable oil pressures, the Reynolds equation is modified to accomodate the terms related to
the controllable oil injection pressures and orifice distribution on the bearing surface. The active bearing forces and the dynamics of the oil injection system are coupled to the set of nonlinear equations that describes the dynamics of the reciprocating engine, obtained with the help of multibody dynamics (rigid components) and finite elements method (flexible components), and the global system
of equations is numerically solved. The analysis of the results was carried out with focus on the behaviour of the journal orbits, maximum fluid film pressure minimum fluid film thickness. The reduction in the cyclic averaged power consumption due to viscous friction forces is also studied.
The modelling of two oil injection systems is presented in the work. The main governing equations of the dynamics of a piezo-actuated oil injection system and a mechanical-actuated unit injector are developed. It is shown how the dynamics of the oil injection system is coupled to the
dynamics of the bearing fluid film through equations. Applying controllable radial oil injection to dynamically loaded journal bearings helps: a) to reduce friction losses by increasing the fluid film thickness; b) to reduce vibrations (i.e., smaller journal centre orbits); and c) to increase the effective carrying load area by modifying the pressure distribution profile, which can make it possible to use bearings of smaller dimensions with similar load-carrying capacity.Brugen af aktiv smøring i glidelejer forøger tykkelsen af smørefilmen, hvorved tab fra viskos friktion og vibrationer mindskes. Konventionel hydrodynamisk smøring kombineret med dynamisk modificeret hydrostatisk smøring, kaldes aktiv smøring. Her modificeres den hydrostatiske smøring
ved at injicere olie igennem dyser i lejets overflade.
For at studere egenskaberne af glidelejer i stempel maskiner under konventionelle smøringsbetingelser er en matematisk model af en krumtapmekanisme forbundet til en stiv / fleksibel rotor via en væskefilm udarbejdet. Den matematiske model involverer brugen af “multi-body-dynamic” teori til modelleringen af en krunmtapmekanisme, “Finite Element” metoden bruges til modellering af den fleksible rotor (krumtappen) og hydrodynamisk smørefilmteori bruges til at beskrive dynamikken af væskefilmen. Når aktiv smøring introduceres for at modificere den konventionelle hydrodynamiske smøring, ved hjælp af radial indsprøjtning af olie, modificeres Reynolds ligning med led der beskriver indsprøjtningen. De aktive lejekræfter og dynamikken af olieindsprøjtningssystemet kobles til systemet af ikke lineære ligninger der beskriver dynamikken af den stempelmaskinen, som er udledt ved hjælp af “Finite Element” metoden. Efterfølgende løses systemet numerisk.
Analysen af resultaterne baserer sig på undersøgelse af lejesølernes bevægelse i lejerne, maksimalt smørefilmtryk og minimum smørefilmtykkelse. Reduktionen af det gennemsnitlige energiforbrug fra viskose kræfter studeres ligeledes.
Modelleringen af to olieindsprøjtningssystemer præsenteres i dette arbejde. De vigtigste beskrivende ligninger for et dynamisk piezo-aktueret olieindsprøjtningssystem og en mekanisk aktueret injektor udledes. Det vises hvordan dynamikken af et olieindsprøjtningssystem kobles matematisk
til lejet. Ved anvendelse af radial olieindsprøjtning i dynamisk belastede glidelejer opnås det at: a) friktionstabet reduceres, da filmtykkelsen øges; b) vibrationer mindskes (dvs. lejesølens bevægelsesamplitude mindskes); og c) at den effektivt bærende flade øges ved modifikation af trykprofilen, hvilket gør det mulig at bruge mindre lejer med uændret bæreevne. |
| Publiceret:
|
|
| Fil(er):
|
|
|
|