Lash adjuster

Abstract

A lash adjuster is provided in which the friction coefficient between the pressure flanks is less likely to decrease over a long time use. The lash adjuster 1 includes a nut member 10 having an internal thread 17 on its inner periphery, an adjusting screw 11 having an external thread 18 on its outer periphery which is in threaded engagement with the internal thread 17 , and a return spring 12 biasing the adjusting screw 11 in a direction to protrude from the nut member 10 , the external thread 18 and the internal thread 17 having pressure flanks 19 and 21 , respectively, for receiving an axial load that tends to push the adjusting screw 11 into the nut member 10 , wherein a satin finished surface is formed on the pressure flank 19 of the external thread 18 , and the satin finished surface has a higher surface hardness than the pressure flank 21 of the internal thread 17.

1 . A lash adjuster comprising a nut member ( 10 ) having an internal thread ( 17 ) on its inner periphery, an adjusting screw ( 11 ) having an external thread ( 18 ) on its outer periphery which is in threaded engagement with the internal thread ( 17 ), and a return spring ( 12 ) biasing the adjusting screw ( 11 ) in a direction to protrude from the nut member ( 10 ), said external thread ( 18 ) and said internal thread ( 17 ) having pressure flanks ( 19  and  21 ), respectively, for receiving an axial load that tends to push the adjusting screw ( 11 ) into the nut member ( 10 ), characterized in that a satin finished surface is formed on one of the pressure flank ( 19 ) of the external thread ( 18 ) and the pressure flank ( 21 ) of the internal thread ( 17 ), and that the satin finished pressure flank has a higher surface hardness than the other of said pressure flanks ( 19  and  21 ). 
     
     
         2 . The lash adjuster of  claim 1  wherein said return spring ( 12 ) is a compression coil spring axially biasing the adjusting screw ( 11 ), said external thread ( 18 ) and said internal thread ( 17 ) having a serration-shaped section, with said pressure flanks ( 19  and  21 ) having a larger flank angle than clearance flanks ( 20  and  22 ) of the external thread and said internal thread, respectively. 
     
     
         3 . The lash adjuster of  claim 1  wherein said return spring is a torsion spring ( 76 ) for applying torque to the adjusting screw ( 11 ) that tends to protrude the adjusting screw ( 11 ) from the nut member ( 10 ). 
     
     
         4 . The lash adjuster of  claim 1  wherein said satin finished surface has a surface roughness Ra of 1.6 to 12.5. 
     
     
         5 . The lash adjuster of  claim 1  wherein said satin finished surface is formed by shot peening. 
     
     
         6 . The lash adjuster of  claim 1  wherein the satin finished pressure flank ( 19 ) is coated with a hard film ( 27 ) and has a higher surface hardness than the other pressure flank ( 21 ). 
     
     
         7 . The lash adjuster of  claim 6  wherein said hard film ( 27 ) is one of a titanium nitride film, a chromium nitride film, a diamond-like carbon film and a ceramic film. 
     
     
         8 . The lash adjuster of  claim 1  wherein the satin finished pressure flank ( 19 ) is subjected to carbonitriding treatment so that the satin finished surface flank ( 19 ) has a higher surface hardness than the other pressure flank ( 21 ). 
     
     
         9 . The lash adjuster of  claim 1  wherein the satin finished pressure flank ( 19 ) is subjected to WPC treatment so that the satin finished surface flank ( 19 ) has a higher surface hardness than the other pressure flank ( 21 ). 
     
     
         10 . The lash adjuster of  claim 1  wherein a backlash of 0.1 to 0.4 mm is defined between the external thread ( 18 ) and the internal thread ( 17 ). 
     
     
         11 . The lash adjuster of  claim 1  further comprising a lifter body ( 9 ) vertically slidably inserted in a guide hole ( 13 ) formed in a cylinder head ( 2 ), wherein said nut member ( 10 ) is fixed to said lifter body ( 9 ), and wherein said adjusting screw ( 11 ) has an end protruding from the nut member and pressing a valve stem ( 5 ) of a valve gear. 
     
     
         12 . The lash adjuster of  claim 1  wherein the nut member ( 35 ) is inserted in a mounting hole ( 38 ) formed in a bottom surface of an arm ( 33 ) that pivots as a cam ( 15 ) rotates, and wherein said adjusting screw ( 36 ) has an end protruding from the nut member ( 35 ) and pressing a valve stem ( 5 ) of a valve gear. 
     
     
         13 . The lash adjuster of  claim 1  wherein the nut member ( 53 ) is inserted in a mounting hole ( 56 ) formed in a top surface of a cylinder head ( 2 ), and wherein said adjusting screw ( 54 ) has an end protruding from the nut member ( 53 ) and pivotally supporting an arm ( 52 ) of a valve gear.