Patent ID: 7727098

Claim:
A chain tensioner comprising a housing defining a cylinder chamber having a closed end and an open end, a cylindrical plunger having a closed front end and slidably received in said cylinder chamber, said cylinder chamber having an annular seal groove formed in an inner periphery thereof near said open end, a seal member received in said seal groove for sealing a gap between sliding surfaces of said cylinder chamber and said plunger, thereby preventing leakage of lubricating oil filling said cylinder chamber, a nut member mounted in said cylinder chamber and having an internal thread formed on an inner periphery thereof, a return spring mounted in said cylinder chamber for pressing said nut member against said closed end of said cylinder chamber and biasing said plunger outwardly of said housing, a screw rod having an external thread formed on an outer periphery thereof and in threaded engagement with said internal thread of said nut member, a rod spring mounted behind said screw rod for biasing said screw rod toward said closed front end of said plunger, each of said internal thread of said nut member and said external thread of said screw rod comprising a pressure flank for receiving a pushing force applied from said plunger to said screw rod, and a clearance flank, said pressure flank having a greater flank angle than said clearance flank, each of said internal thread and said external thread having a serration-shaped longitudinal section, and a damper mounted between a front end of said screw rod and said closed front end of said plunger for damping, in cooperation with said return spring, a pushing force applied to said plunger, and for allowing said screw rod and said plunger to move relative to each other in a direction in which the distance between respective remote ends thereof decreases by an amount not less than an axial play present between said internal and external threads, wherein said damper comprises a stopper for restricting the relative movement between said screw rod and said plunger in said direction, and wherein said damper comprises a cylindrical body having a rear open end opposing said screw rod and having a radially inwardly bent piece formed at said rear open end, said stopper, which is axially slidably mounted in said cylindrical body and prevented from coming out of said cylindrical body by said inwardly bent piece, and a spring member biasing said stopper toward said bent piece.