Research On Dynamic Performance, Thermal Performance And Fatigue Life Calculation Method For Automobile Water Pump Bearing

The coaxial water pump bearing is widely used in the water cooling systems of the combustion engines of automobiles, textile machines and construction machines due to its compact structure, easy installation and so on. More excellent operating performances of this bearing such as higher running accuracy, better heat resistance and longer fatigue life are required to satisfy the development of modern combustion engines. However, how to accurately evaluate these operating perpormances in the specific bearing applications and eventually optimize the bearing design is a difficult problem puzzling bearing engineers and so it is always a research hotspot in the rolling bearing industry. In this dissertation, the automobile water pump bearing is taken as the research object. The loads and motions of bearing components, the dynamic and theromal performances of the bearing-rotor system, and the bearing fatigue life are investigated in detail. The research contents and achievements of this dissertation include following aspects:(1) A new calculation model based on flexible-hydrodynamic condition is established to accurately and rapidly calculate the loadings, internal load distributions and displacements of the automobile water pump bearing, in which the deflection of bearing spindle, the hydrodynamic effects at raceway-rolling element contacts, the centrifugal forces of rolling elements and the alterable clearances of bearing are all considered. Making use of this model, the influence rules of the deflection of the bearing spindle, the hydrodynamic effect, the bearing rotational speed and the load carried by the bearing on the bearing internal load distributions and displacements are specifically studied.(2) Taking the influences of the spindle deflection and lubrication film into consideration, the theoretical calculation methods of the bearing stiffnesses and dampings along various directions are derived for water pump bearings running under different speeds and loads. A modified transfer matix method is developed to analyze the vibration characteristics of the asymmetric rotor-water pump bearing system, considering the rotary inertias and gyroscopic moments of all components within the rotor system and the bearing stiffnesses and dampings related to the bearing speed and load. With this modified method, the vibrations of the rotor-water pump bearing system due to the mass unbalances of system components and the varying compliance (VC) of the bearing are calculated and analyzed. The response amplitudes under different bearing rotational speeds, the frequency spectra and axis orbits of two rolling element rows of the bearing are obtained. The influences of the cooling fan and driving pulley unbalanes including their magnitudes and azimuths on the vibration of the rotor-water pump bearing system are also investigated and the optimum azimuth differences and magnitude ratios between the fan and pulley unbalances are obtained to minimize the vibration responses at individual axial positons along the rotor. (3) An improved quasi-dynamic model used to calculate the heat generations of the water pump bearing is proposed. In this model, the influence of the spindle deflection, the lubricant hydrodynamic effect and rolling element centrifugal forces on the bearing internal load distribution and the influence of contact ellipse truncation and lubrication starvation on the hydrodynamic rolling force at each rolling element-raceway contact are all considered.The analysis of water pump bearing heat generation performance are conducted by an example calculation. The sliding frictional shear stress distributions over the rolling element-raceway contacts, cage pocket-rolling elment normal contact loads and heat generation rates at all rolling elment azimuth angles, and the relationship curves of the bearing total heat generation rate versus the bearing speed and load are obtained.(4) An experimental apparatus is designed and built to test the temperature rises of the water pump bearing under different operating conditions. According to the heat generation rates calculated with the improved quasi-dynamic model, transient thermal analysis for this apparatus is performed using a network approach. The temperature rises of the bearing outer ring got from the thermal analysis agree well with those measured from the experimental apparatus and so the heat generation calculation model developed for the water pump bearing is validated.(5) The individual fatigue lives of the bearing components and then the total fatigue live of the bearing are predicted based on the systems approach of bearing fatigue life calculation proposed by the ISO standard and further considering the nonstandard internal load distributions of the bearing and the vibrations of the rotor-bearing system. The influence rules of the spindle deflection, the hydrodynamic effects, the bearing rotational speed and the rotor-bearing system vibrations on the fatigue life of the water pump bearing are obtained.The researches and achievements obtained in this dissertation can provide theoretical foundations for evaluating the operation performances of the water pump bearing accurately and further for optimizing the bearing design and matching the practical operating conditions reasonably for the bearing.