Hybrid hydrostatic axial thrust bearing

#1. Field of the Invention

#The invention relates to a hydrostatic axial thrust bearing which includes an anti-friction bearing for supporting at least part of the bearing load when the load is too large for the pressurized fluid in the bearing.

#2. Description of the Prior Art

#FIGS. 1 and 2 each show a hydrostatic axial thrust bearing including an anti-friction bearing for taking up at least some of the bearing load under certain load conditions; and

#FIG. 3 is a top view of an area below the race of the anti-friction bearing, that is a view along lines III--III of FIG. 2.

#FIG. 1 shows a hydrostatic axial thrust bearing in which a support member 2 supports a load member 4 by a bearing structure disposed between the support and load members 2 and 4. The load member 4 has a cavity 6 formed therein into which pressurized fluid is admitted through a pressurized fluid passage 8, which may be arranged in either the support or the load member. Escape of pressurized fluid from the load cavity 6 is normally permitted only through the limited leakage seal passage 10 formed between surfaces of the load member 4 and a limited leakage seal ring 12 which is movably disposed in, and sealed against the walls of, the cavity 6. The seal ring 12 contains the pressurized fluid under pressure within the load cavity 6 and the pressurized fluid normally carries the full load of the load member 4. The limited leakage seal ring 12 is preferably biased by springs 14 toward the load member 4 in order to readily permit pressurization of the load cavity during start-up. It is provided with an orifice 16 permitting pressurized fluid to flow into the space 18 behind the seal ring so as to balance the pressure of the leakage fluid in the limited leakage fluid path between the seal ring 12 and the load member 4. The seal ring has its opposite faces so sized that upon pressurization of the load cavity, its distance from the load member 4 is automatically adjusted to provide only a small gap for a small leakage flow. In order to prevent overpressurization of the cavity and over-loading of the pressurized fluid source as it may be caused by overloads of the axial thrust bearing, there is provided a pressure relief valve 20 which opens when a predetermined pressure is reached; that is when the bearing load reaches a predetermined value. The relief pressure is adjustable by changing the force of spring 22 by means of an adjustment screw 24. Within the bearing cavity 6 there is further provided an anti-friction bearing 26 having an annular race 28 supported on the support member 2. Two O-rings 30 and 32 are disposed below the race 28 and a vent passage 34 provides communication between the area under the race 28 and a low pressure area to prevent undesired floating of the annular race 28 when the load member is supported solely by the pressurized fluid in the cavity 6.

#Under light load, the load member 4 is raised off the support member and the limited leakage seal ring 12 follows the movement of the load member 4. The limited leakage seal ring 12, however, is provided with a flange 36 projecting radially inwardly under the annular race 28 which thereby restricts the movement of the leakage seal ring 12. This, at the same time, restricts lift-off of the load member 4 as further raising of the load member results in an increased leakage gap 10 and increased leakage rates which would limit the pressure of the pressurized fluid in the load cavity to the value needed to carry the load.

#If, on the other hand, the load member increases beyond the predetermined value the fluid pressure is not permitted to rise beyond the predetermined value; rather the relief valve 20 is opened so that pressurized fluid is discharged from the load cavity and the load member settles down onto the anti-friction bearing 26. The fluid pressure in the load cavity remains at the limit providing for a predetermined maximum load member support force. Any excess load is taken up by the anti-friction bearing.