Seal assembly for roller cutter drill bit having a pressure balanced lubrication system

Claim 1

A rotary drill bit comprising: a bit body having a journal extending therefrom and a roller cutter mounted for rotation on said journal, said journal forming a first bearing member and said roller cutter forming a second bearing member; an annular pocket formed between said journal and roller cutter generally at the juncture of said journal and bit body; a lip on one of the bearing members defining a peripheral surface forming a portion of said annular pocket; a lubricant system including a lubricant reservoir in said bit body, fluid pressure compensating means in said reservoir for effecting a balancing of fluid pressure between drilling fluid outside the bit and lubricant inside the bit, and lubricant passages between said lubricant reservoir and said pocket for providing lubricant thereto; and a floating seal assembly mounted within said pocket for sealing between said journal and said roller cutter, said seal assembly including a pair of rigid seal rings in said pocket in face to face sealing contact with each other and having adjacent inner peripheral surfaces in side by side relation, and a pair of elastomeric seal rings in side by side relation on said adjacent inner peripheral surfaces of said rigid seal rings in sealing contact with said adjacent inner peripheral surfaces of said rigid seal rings and continuously urging said rigid seal rings into face to face sealing contact, said elastomeric seal rings separating said pocket into a lubricant chamber and a drilling fluid chamber, the fluid pressure in one chamber acting in opposed relation to said elastomeric seal rings for urging said elastomeric seal rings away from each other and the fluid pressure in the other chamber acting in opposed relation to said elastomeric seal rings for urging said elastomeric seal rings toward each other to maintain sealing relation of said rigid seals; said lubricant passages to said lubricant chamber pocket being of sufficient cross sectional area to maintain the fluid pressure differential between a relatively low pressure drilling fluid outside the bit and a relatively high pressure lubricant inside the bit resulting from a rapid axial movement of said roller cutter from an outermost position on said journal to an innermost position at a minimal amount sufficient to maintain said rigid seal rings in sliding sealing contact during normal operation of the drill bit; said floating seal assembly moving axially back and forth in said pocket upon axial movement of said roller cutter relative to said journal, the axial back and forth movement of said seal assembly being around 1/2 the axial back and forth movement of said roller cutter on said journal thereby to minimize wear of said elastomeric seal rings.