Hydrostatic/hydrodynamic bearings are widely applied for HDD, grinding machines and marine diesel engine and so on because of high load carrying capacity, superior running accuracy and excellent dynamic characteristics. Various factors such as vibration from driving systems, unbalance of assembling and machining error of a bearing affect running accuracy of bearing systems. Many researchers tried to analyze running accuracy of bearings. But main reason of shaft shape that has waviness error and therefore causes running accuracy is not still investigated.
So the waviness error effect of a journal and a bearing is investigated in this study. That causes the alteration of oil film thickness profile, as a result pressure distribution of a bearing changes. Cosine functions are selected to express waviness of a journal and a bearing because error components of a journal and a bearing repeat periodically. By analyzing Reynolds equation, load carrying capacity, pressure distribution, stiffness coefficient and damping coefficient are obtained to examine the waviness effect. As a result, if the shapes of a journal and a bearing are circle, the parameters are constants under particular operation conditions. But if a journal including waviness error components rotates, the parameters change according to the waviness error components of amplitude and period.
Low amplitude and low period of waviness error reduced the change of the parameters. In the case of hydrostatic bearing, reducing maximum pocket pressure had some advantages to run more accurately. As the rotating speed increases, the pressure of a bearing also increases therefore the eccentricity of a shaft decrease. Load increment causes high eccentric operation of a journal.
A bearing tester was fabricated to verify the analysis model. The eccentricity and the attitude angle of theoretical analysis according to load was almost agree with test results. In order to apply theoretical analysis results, hydrostatic bearing for a crankshaft pin turner was introduced. From the basic analysis results, the conditions of flow rate, the radial clearance and the operating eccentricity were determined. The eccentricity variation according to the waviness error of a journal and a bearing was analyzed, as a result in order to operate the running accuracy under 15㎛, the amplitude of a shaft waviness error should not be over 8㎛. From dynamic load condition analysis results of skiving process, it was found out that the phase angles of bearing load and load carrying capacity wave affected the running accuracy. If their phase angles coincided, amplitude of journal waviness error was permitted up to 16 ㎛.