Hiroo Taura

Effect of Texture Region on the Static and Dynamic Characteristic of Partially Textured Journal Bearings

The effect of the texturing region on the static and dynamic characteristics of partially textured bearings, of which the texturing area is limited on the bearing surface in the circumferential direction, were investigate theoretically. The load carrying capacity and stiffness and damping coefficients of some partially textured journal bearings with the different textured region were calculated by using a numerical model considering the effects of both fluid inertia and energy loss at the edges of the dimples. The results showed that when the surface texturing was formed in the unloaded region of the journal bearing surface, the load carrying capacity maintains as much as the smooth bearing for a wide range of Sommerfeld number. The linear stability threshold speeds of a symmetrical rigid rotor supported in two identical textured bearings was also calculated with the dynamic coefficients of the oil film. The results obtained showed that when the texture region starts from 270° from the top of the bearing in the rotating direction, the stability threshold speeds are higher than those of the fully textured bearing at relatively high Sommerfeld number. From these results, it was concluded that an appropriate partial texturing formed on the bearing surface can improve both the load carrying capacity and the stability characteristics simultaneously.

Effect of Square-Dimple Size on Dynamic Characteristics of Textured Journal Bearings

Dynamic characteristics of journal bearings with uniform square dimples on the whole bearing surface are numerically calculated considering the inertia effect and the energy loss based on the oil film discontinuity at the edge of dimples. The comparison of the results with a smooth bearing without dimples shows that all the stiffness and damping coefficients for the textured bearings are smaller than those for the smooth bearing over a wide range of eccentricity ratio. The effects of the number of dimples are investigated under a constant total area of dimples, and the cross-coupled stiffness coefficients decrease significantly at lower eccentricity ratio for the large number of dimples due to the inertia effect and energy loss at the discontinuous dimple edge. The linear stability threshold shaft speeds of a symmetrical rigid rotor increase with the number of dimples, which is attributable to the reduction of the cross-coupled stiffness coefficients.

Lubrication Characteristics of Electric Sliding Contacts Consisting of Rotating Circular Grooved Disk and Stationary Rider With Spherical Surface Under Lubricated Condition

Electric sliding contacts are widely used in various electrical components such as for home appliances and automobiles. The purpose of the present study is to improve the performance characteristics of the electric sliding contacts operating under the lubricated condition by the combination of circular grooved disk and rider with a spherical surface. The experimental and theoretical analyses have been carried out to investigate the effect of cross-sectional area of circular grooves provided in the rotating disk surface on the frictional characteristics and the electrical conductivity. The experimental analysis is conducted with a pin-on-disk friction tester to measure the frictional force and the contact voltage between the sliding contacts under the lubricated condition. The oil-film force and the frictional force between the rider and disk are also calculated with the Reynolds equation and they are found to be closely corresponding to the experimental results. The results obtained in the present study show that increasing the cross-sectional area of the circular grooves on the disk extends the operation condition yielding the metal contact to a higher value of the bearing characteristic number S, which is defined by eta U0L0 lambda/W (eta is the lubricant oil viscosity, U-0 is the sliding velocity, L-0 is the rider arc length in the sliding direction at the middle of radial width, W is the applied load, and lambda is the aspect ratio of rider), and also decreases the frictional force at the maximum value of S at which the rider could contact with the disk surface. These are expected since upstream lubricant oil dragged into the contact region tends to easily leak out along the circular grooves, yielding a lower oil-film force between the rider and disk and enhancing the metal contact.

The Effect of Thin Lubricant Films on Acoustic Emission Characteristics

This paper shows the effect of ultrathin lubricant films between sliding bodies on Acoustic Emission (AE) signals induced by the sliding friction. Experiments were conducted with a ball-on-disk friction tester to measure the friction coefficient, the raw AE signals and the root-mean-squarevalues of the AE signals (the AErms signals). The ball was a glass ball of 5mm diameter. The disk was a magnetic disk used for 2.5 inch HDD with a DLC protective layer on its surface, and was coated with PFPE Z-dol 4000 about 1.5nm thick. The AErms signals kept a low level for some time after the start of the test, and then increased. Its time variation was similar to that of friction coefficient. After the friction test, the circumferential distribution of the lubricant film thickness was measured with an ellipsometer. The distribution demonstrated the reduction of the lubricant film thickness at the circumferential position where the magnitude of AE signals became large. These facts showed that the AE signals correlated well with the lubricant film thickness.Copyright