This thesis work, carried out within the R&D department of the Bosch-Vhit s.p.a. company, regards the study of the axial wear phenomenon occurring on mechanical vacuum pumps, component of the braking system of many vehicles. This wear phenomenon is particularly evident with the use of low viscosity oils, utilized by the OEMs with the aim of reducing the fuel consumption in order to face the more stringent emission standards. The constantly evolving market and the new emissions legislation, requires a continuous improvement of the product from the efficiency and performance point of view. The approach utilized in order to understand this phenomenon consisted in the creation of a numerical model. This is composed by a sub-model representing the oil circuit of the pump and a sub-model that simulates the hydrodynamic thrust bearings. These models provide the forces acting on the rotor, which, combined through a forces balance, allow the computation of the contact forces acting in the wear points. Under specific working conditions, in fact, these contact forces cause an appreciable wear, in particular on the cover of the pumps, and that means a considerable performance decrease. Therefore, through an experimental tests campaign and the comparison between the obtained numerical and experimental results, we are able to characterize the wear trend, establishing a relation between wear, operating conditions of the pump and type of oil. Through the calculation of the wear coefficients, dependent both on the experimental data and on the simulation results, we will finally have a model able to give an evaluation of the wear volume on the cover of the pump. This model can provide results for given working conditions and degradation level of the oils, assessed with chemical analysis on the new and exhausted ones.
Questo lavoro di tesi, svolto presso il dipartimento di Ricerca e Sviluppo dell’azienda Bosch-Vhit S.p.A, riguarda lo studio del fenomeno di usura assiale sulle pompe del vuoto meccaniche, un componente del sistema frenante presente su molti veicoli. Il fenomeno dell’usura su queste pompe si rivela essere accentuato utilizzando oli poco viscosi, usati dagli OEMs con lo scopo di ridurre il consumo di combustibile in modo da poter far fronte alle sempre più stringenti normative riguardanti le emissioni. Il mercato in continua evoluzione e i nuovi standard sulle emissioni richiedono infatti all’azienda un continuo miglioramento dei prodotti in termini di efficienza e performance. L’approccio utilizzato per caratterizzare il fenomeno consiste nello sviluppo di un modello numerico. Questo modello è costituito da un primo sotto-modello rappresentante il circuito dell’olio della pompa e da un secondo sotto-modello che simula i cuscinetti idrodinamici assiali. Questi modelli forniscono le forze agenti sul rotore, le quali, combinate attraverso un bilancio di forze, permettono il calcolo delle forze agenti nei punti di usura. Sotto specifiche condizioni operative, infatti, queste forze di contatto provocano un’usura considerevole, in particolare sul coperchio delle pompe e ciò determina una consistente diminuzione delle performance. Quindi, attraverso una campagna di test sperimentali ed il confronto tra i risultati numerici e sperimentali ottenuti, è possibile caratterizzare l’andamento dell’usura, stabilendo una relazione tra usura, condizioni operative della pompa e tipo di olio utilizzato. Attraverso il calcolo dei coefficienti di usura, dipendenti sia dai dati sperimentali che dai risultati della simulazione, si avrà infine un modello in grado di fornire una valutazione del volume usurato sul coperchio della pompa. Questo modello fornisce risultati in base alle condizioni operative ed al livello di degrado dell’olio, verificato attraverso analisi chimiche su olio nuovo ed esausto.
Experimental and numerical study on the axial wear of rotary-vane vacuum pumps
BODINI, RICCARDO
2018/2019
Abstract
This thesis work, carried out within the R&D department of the Bosch-Vhit s.p.a. company, regards the study of the axial wear phenomenon occurring on mechanical vacuum pumps, component of the braking system of many vehicles. This wear phenomenon is particularly evident with the use of low viscosity oils, utilized by the OEMs with the aim of reducing the fuel consumption in order to face the more stringent emission standards. The constantly evolving market and the new emissions legislation, requires a continuous improvement of the product from the efficiency and performance point of view. The approach utilized in order to understand this phenomenon consisted in the creation of a numerical model. This is composed by a sub-model representing the oil circuit of the pump and a sub-model that simulates the hydrodynamic thrust bearings. These models provide the forces acting on the rotor, which, combined through a forces balance, allow the computation of the contact forces acting in the wear points. Under specific working conditions, in fact, these contact forces cause an appreciable wear, in particular on the cover of the pumps, and that means a considerable performance decrease. Therefore, through an experimental tests campaign and the comparison between the obtained numerical and experimental results, we are able to characterize the wear trend, establishing a relation between wear, operating conditions of the pump and type of oil. Through the calculation of the wear coefficients, dependent both on the experimental data and on the simulation results, we will finally have a model able to give an evaluation of the wear volume on the cover of the pump. This model can provide results for given working conditions and degradation level of the oils, assessed with chemical analysis on the new and exhausted ones.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/148779