Thrust face lubrication system for a rolling cutter drill bit

A rolling cutter drill bit comprising a body and a plurality of legs, at least one of said legs having a cantilevered bearing spindle, a rolling cutter rotatably mounted on the bearing spindle, bearing means located between the cutter and the spindle and including a thrust bearing configured to carry onward thrust loads from the cutter onto the spindle, bearing seal means defining an enclosed region between the cutter and the spindle in which said bearing means are located, and lubricant delivery means within the spindle to deliver lubricant to the bearing means, said lubricant delivery means including flow control means to allow lubricant to flow into an area of said enclosed region containing the thrust bearing and to restrict the flow of lubricant out of said thrust bearing area and into another area of said enclosed region, said flow control means including an inlet flowpath leading to said thrust bearing area and valve means controlling the flow of lubricant along said inlet flowpath, said valve means comprising a non-return valve arranged to permit flow of lubricant along said inlet flowpath and into said thrust bearing area and substantially to prevent flow of lubricant back along said flowpath away from the thrust bearing area, there being provided a restricted outlet flowpath, leading away from said thrust bearing area, which is separate from said inlet flowpath and includes a tortuous path provided by a flexibly resilient sealing ring between the bearing spindle and the rolling cutter.

A rolling cutter drill bit comprising a body and a plurality of legs, at least one of said legs having a cantilevered bearing spindle, a rolling cutter rotatably mounted on the bearing spindle, bearing means located between the cutter and the spindle and including a thrust bearing configured to carry onward thrust loads from the cutter onto the spindle, bearing seal means defining an enclosed region between the cutter and the spindle in which said bearing means are located, and lubricant delivery means within the spindle to deliver lubricant to the bearing means, said lubricant delivery means including flow control means to allow lubricant to flow into an area of said enclosed region containing the thrust bearing and to restrict the flow of lubricant out of said thrust bearing area and into another area of said enclosed region, said flow control means including an inlet flowpath leading to said thrust bearing area and valve means controlling the flow of lubricant along said inlet flowpath, said valve means comprising a non-return valve arranged to permit flow of lubricant along said inlet flowpath and into said thrust bearing area and substantially to prevent flow of lubricant back along said flowpath away from the thrust bearing area, there being provided a restricted outlet flowpath, leading away from said thrust bearing area, which is separate from said inlet flowpath, said bearing means further including a radial bearing located within the bearing region and configured to carry radial loads from the cutter onto the spindle, said restricted outlet flowpath being located, at least in part, between said thrust bearing area and an area of the bearing region containing said radial bearing, and including a tortuous path provided by a flexibly resilient sealing ring between the bearing spindle and the rolling cutter, said sealing ring being located on the opposite side of said radial bearing to said thrust bearing.