Experimental Study of Limited Oil Supply on Lubrication Characteristics under Velocity Intersection Working Condition

This article was focused on the effects of the velocity intersection condition on elastohydrodynamic film thickness under limited lubricant supply. The velocity intersection condition referred to the situation that there was an angle between two solid surface velocities of the contact area in moving tribo-elements. The lubrication behavior was different to most common contact pairs for their special profile structure like hypoid gear. Furthermore, under the condition of limited oil supply, velocity intersection condition played an important role on lubricant migration and lubrication state. By using the point contact EHL test rig with intersection of surface velocities, the steel ball transmission device was rotated by a specific angle through an arc guide rail (the entrainment and sliding behaviors of two solid surfaces were changed to obtain different intersection angles ε), and the influence of the angle on the lubricating oil film and boundary of oil pool was studied. The test results showed that under the limited oil supply, parts of lubricant were redistributed to the contact area to participate in film formation and the lubrication state was significantly improved when the entrainment and sliding velocity had a certain intersecting angle. It was caused by the lateral transportation of lubricant formed by the intersection of lubricating raceway. With the increase of the angle ε, the lubrication state was first increased and then weakened, which was optimal at the angle range of 45°~135°. Under the limited oil supply, the velocity intersection effect was helpful to form higher central film thickness but was not conducive to symmetry of oil pool. The asymmetry of oil pool shape stemmed from the linear velocity difference between the two solid surfaces. When the surface velocity direction was parallel (ε=0°or 180°), the starvation occurred, which weakens effected of the entrainment velocity on lubricating oil film thickness. After changing the velocity angle, the oil film thickness increased significantly and the oil pool boundary decreased slightly with the increase of entrainment velocity. At the same time, the lubricant viscosity had a great influence on the replenishment. Low viscosity lubricant had great spontaneous backward flowing ability due to its high fluidity characteristics, but its intersection effect was not obvious. As viscosity increased, the intersection condition affected the oil supply to the contact area. However, lubricant with high viscosity had poor fluidity, which led to a less lubrication efficiency. And the amount of oil supplied to the contact area was another factor to the film formation under velocity intersection condition. Under velocity intersection condition, when the oil supply reaches 2 μl, the variation curve of film thickness with oil supply was basically stable. And when the oil supply reaches to 5 μl, the oil film thickness curve was basically consistent with fully flooded condition. The extremely low oil supply (0.1 μl) limited the lubrication enhancement of velocity intersecting effect, and the limited oil pool boundary weakens the effective intersection of lubricants on both sides, which results in satellite droplets could not enter the contact area to participate in lubrication.