Lash adjuster

Abstract

A lash adjuster is provided of which the return spring is never compressed excessively when the adjusting screw is pushed into the nut member, and of which the external thread on the outer periphery of the adjusting screw can be formed easily by rolling. The lash adjuster 1 includes a nut member 12 having an internal thread 13 , an adjusting screw 15 having an external thread 14 on its outer periphery which is in threaded engagement with the internal thread 13 , and a return spring 17 biasing the adjusting screw 15 in the direction to protrude from the nut member 12 . The adjusting screw 15 pivotally supports an arm 7 of a valve gear at its end protruding from the nut member 12 . The adjusting screw 15 has at its portion protruding from the nut member 12 a stopper portion 23 having a larger diameter than the inner diameter of the nut member 12 . By supporting the stopper portion 23 on the open end of the nut member 12 , it is possible to restrict the movement of the adjusting screw 15 when the adjusting screw 15 is pushed into the nut member 12.

1 . A lash adjuster comprising a nut member ( 12 ) having an internal thread ( 13 ) on its inner periphery, an adjuster screw ( 15 ) having an external thread ( 14 ) on its outer periphery which is in threaded engagement with the internal thread ( 13 ), and a return spring ( 17 ) biasing the adjusting screw ( 15 ) in a direction to protrude from the nut member ( 12 ), wherein an axial load that tends to push the adjusting screw ( 15 ) into the nut member ( 12 ) is received by pressure flanks ( 18 ) of the external thread ( 14 ) and the internal thread ( 13 ),
 characterized in that the adjusting screw ( 15 ) has a stopper portion ( 23 ) at its portion protruding from the nut member ( 12 ), said stopper portion ( 23 ) having a diameter larger than the inner diameter of the nut member ( 12 ), wherein the nut member ( 12 ) has an open end configured to support the stopper portion ( 23 ), thereby restricting movement of the adjusting screw ( 15 ) when the adjusting screw ( 15 ) is pushed into the nut member ( 12 ).   
     
     
         2 . The lash adjuster of  claim 1  wherein the stopper portion ( 23 ) has a tapered surface ( 24 ) on its outer periphery which is configured to abut a tapered surface ( 25 ) formed on the open end of the nut member ( 12 ). 
     
     
         3 . The lash adjuster of  claim 1  wherein the stopper portion ( 23 ) has a flat surface ( 26 ) on its outer periphery which extends perpendicular to an axial direction and configured to abut a flat surface ( 27 ) formed on the open end of the nut member ( 12 ) so as to extend perpendicular to the axial direction. 
     
     
         4 . The lash adjuster of  claim 1  wherein the stopper portion ( 23 ) comprises a snap ring ( 28 ) fitted on the outer periphery of the portion of the adjusting screw ( 15 ) protruding from the nut member ( 12 ). 
     
     
         5 . The lash adjuster of  claim 1  wherein the return spring ( 17 ) is a compression spring that applies an axial force to the adjusting screw ( 15 ) that tends to push the adjusting screw ( 15 ) out of the nut member ( 12 ), and wherein the external thread ( 14 ) and the internal thread ( 13 ) have a serration-shaped section with their pressure flanks ( 18 ) having a larger flank angle than their clearance flanks ( 19 ). 
     
     
         6 . The lash adjuster of  claim 1  wherein the return spring ( 17 ) is a torsion spring that applies torque to the adjusting screw ( 15 ) that tends to push the adjusting screw ( 15 ) out of the nut member ( 12 ), and wherein the external thread ( 14 ) and the internal thread ( 13 ) are serration-shaped threads, trapezoidal threads or triangular threads. 
     
     
         7 . The lash adjuster of  claim 6  wherein the torsion spring is one of a torsion coil spring, a spiral spring and a volute spring. 
     
     
         8 . The lash adjuster of  claim 1  wherein the nut member ( 12 ) is inserted in a receiving hole ( 11 ) formed in a top surface of a cylinder head ( 2 ), and wherein the adjusting screw ( 15 ) pivotally supports an arm ( 7 ) of a valve gear at its end protruding from the nut member ( 12 ). 
     
     
         9 . The lash adjuster of  claim 1  wherein the nut member ( 41 ) is fixed to a lifter body ( 40 ) vertically slidably inserted in a guide hole ( 39 ) formed in a cylinder head ( 32 ), and wherein the adjusting screw ( 44 ) presses a valve stem ( 35 ) of a valve gear at its end protruding from the nut member ( 41 ). 
     
     
         10 . The lash adjuster of  claim 1  wherein the nut member ( 73 ) is inserted in a receiving hole ( 76 ) formed in a bottom surface of an arm ( 67 ) that pivots as a cam ( 71 ) rotates, and wherein the adjusting screw ( 74 ) presses a valve stem ( 65 ) of a valve gear at its end protruding from the nut member ( 73 ). 
     
     
         11 . The lash adjuster of  claim 1  wherein the adjusting screw ( 15 ) comprises a pivot member ( 15 A) axially slidably inserted in the nut member ( 12 ), an externally threaded member ( 15 B) supporting an end of the pivot member ( 15 A) located in the nut member ( 12 ) and having said external thread ( 14 ) on its outer periphery, and an elastic member ( 15 C) disposed between the pivot member ( 15 A) and the externally threaded member ( 15 B). 
     
     
         12 . The lash adjuster of  claim 11  wherein the pivot member ( 15 A) has a square hole ( 96 ) formed in its end located in the nut member ( 12 ), and wherein the externally threaded member ( 15 B) has a square shaft ( 97 ) engaged in said square hole ( 96 ), whereby the pivot member ( 15 A) and the externally threaded member ( 15 B) are rotatable together due to the engagement of the square shaft ( 97 ) in the square hole ( 96 ).