Rocker arm structure

Abstract

A rocker arm arranged between a camshaft and a valve which opens/closes an intake port or an exhaust port. A rolling bearing for supporting a support hole formed in a rocker arm is of a type of bearing wherein a plurality of needles are mounted on an inner side of an outer peripheral shell, and the outer peripheral shell is fixed to the support hole, the cam follower includes an outer ring which is supported on a periphery of a cam follower shaft which is held by a pair of left and right arm portions of the rocker arm by way of a plurality of rollers, a position of the outer ring and a position of the rollers in the lateral direction are restricted by the arm portion, and an outer diameter of the outer ring is set equal to or less than an inner diameter of the support hole.

1 . A structure of a rocker arm of a valve system arranged between a camshaft and a valve for opening/closing an intake port or an exhaust port in an internal combustion engine, wherein the rocker arm comprises:
 a support hole for enabling rockable supporting of the rocker arm by a rocker shaft supported on a cylinder head; and a cam follower receiving a pushing force from a cam of the camshaft, the support hole and the cam follower being supported by a rolling bearing structure;
 a rolling bearing for supporting the support hole includes a bearing having a plurality of needles mounted on an inner side of an outer peripheral shell, the outer peripheral shell being fixed to the support hole; 
 the cam follower comprises an outer ring supported on a periphery of a cam follower shaft held by a pair of left and right arm portions of the rocker arm by a plurality of rollers, a position of the outer ring and a position of the rollers in the lateral direction being restricted by the arm portion, and 
 an outer diameter of the outer ring is set equal to or less than an inner diameter of the support hole. 
   
     
     
         2 . The structure of the rocker arm according to  claim 1 , wherein an escape portion is formed on the rocker arm so that the rocker arm does not obstruct the movement of a distal end of a cam nose when the camshaft is rotated. 
     
     
         3 . The structure of the rocker arm according to  claim 1 , wherein in an exhaust-side rocker arm out of the rocker arm, a decompression device is engaged with the exhaust-side rocker arm and is mounted on the camshaft, a decompression shaft portion of a decompression cam which the decompression device includes is supported on an inner side of an outer peripheral surface of a base circle portion of the exhaust cam, and the decompression cam applies a decompression action to a projecting portion of an arm portion of the exhaust-side rocker arm. 
     
     
         4 . The structure of the rocker arm according to  claim 2 , wherein in an exhaust-side rocker arm out of the rocker arm, a decompression device is engaged with the exhaust-side rocker arm and is mounted on the camshaft, a decompression shaft portion of a decompression cam which the decompression device includes is supported on an inner side of an outer peripheral surface of a base circle portion of the exhaust cam, and the decompression cam applies a decompression action to a projecting portion of an arm portion of the exhaust-side rocker arm. 
     
     
         5 . The structure of the rocker arm according to  claim 3 , wherein the arm portions of the exhaust-side rocker arm are formed wherein, compared to a width of the arm portion on a side where the arm portions is brought into contact with the decompression cam, a width of the arm portion on the other side is set small. 
     
     
         6 . The structure of the rocker arm according to  claim 2 , wherein the internal combustion engine is an internal combustion engine where the camshaft and the rocker shaft are arranged in front of a combustion chamber and in a planar projection view as viewed in the cylinder axis direction, with respect to each rocker arm, a size between an axis of the rocker shaft and an axis of the cam follower shaft is set smaller than a size between the axis of the rocker shaft and an axis of the camshaft. 
     
     
         7 . The structure of the rocker arm according to  claim 5 , wherein the rocker shaft is fixed to the cylinder head by fastening in a non-rotatable manner. 
     
     
         8 . The structure of the rocker arm according to  claim 1 , wherein the cam follower shaft of the cam follower is formed of a solid small-diameter shaft and a thickness of the outer ring in the radial direction is set smaller than a diameter of the roller. 
     
     
         9 . The structure of the rocker arm according to  claim 2 , wherein the cam follower shaft of the cam follower is formed of a solid small-diameter shaft and a thickness of the outer ring in the radial direction is set smaller than a diameter of the roller. 
     
     
         10 . The structure of the rocker arm according to  claim 4 , wherein the respective rocker arms arranged adjacent to each other are formed such that a width of the arm portion on a left side and a width of the arm portion on a right side differ from each other and the width of the inner arm portion is set smaller than a width of the outer arm portion. 
     
     
         11 . The structure of the rocker arm according to  claim 1 , wherein the internal combustion engine is a frontwardly-inclined engine wherein a cylinder axis extends frontwardly and upwardly and oil supply guide walls which lead to an end surface of the support hole of the rocker arm from the rocker shaft support boss portion in a vehicle mounted state are formed in the vicinity of the rocker shaft support boss portions of the cylinder head. 
     
     
         12 . The structure of the rocker arm according to  claim 9 , wherein the oil supply guide walls are arranged close to the rocker shaft support boss portions positioned laterally outside the intake-side rocker arm and the exhaust-side rocker arm arranged parallel to each other in the lateral direction toward an oil supply hole formed in the cylinder head cover. 
     
     
         13 . A rocker arm for a valve system arranged between a camshaft and a valve for opening/closing an intake port or an exhaust port in an internal combustion engine, comprising:
 a support hole formed for rockable supporting the rocker arm on a rocker shaft supported on a cylinder head; and a cam follower receiving a pushing force from a cam of the camshaft, the support hole and the cam follower being supported by a rolling bearing structure;
 a rolling bearing mounted within the support hole includes a plurality of needles mounted on an inner side of an outer peripheral shell, the outer peripheral shell being fixed to the support hole; 
 the cam follower includes an outer ring supported on a periphery of a cam follower shaft held by a pair of left and right arm portions of the rocker arm by a plurality of rollers, a position of the outer ring and a position of the rollers in the lateral direction being restricted by the arm portion, and 
 an outer diameter of the outer ring is set equal to or less than an inner diameter of the support hole. 
   
     
     
         14 . The rocker arm according to  claim 13 , wherein an escape portion is formed on the rocker arm so that the rocker arm does not obstruct the movement of a distal end of a cam nose when the camshaft is rotated. 
     
     
         15 . The rocker arm according to  claim 13 , wherein in an exhaust-side rocker arm out of the rocker arm, a decompression device is engaged with the exhaust-side rocker arm and is mounted on the camshaft, a decompression shaft portion of a decompression cam which the decompression device includes is supported on an inner side of an outer peripheral surface of a base circle portion of the exhaust cam, and the decompression cam applies a decompression action to a projecting portion of an arm portion of the exhaust-side rocker arm. 
     
     
         16 . The rocker arm according to  claim 14 , wherein in an exhaust-side rocker arm out of the rocker arm, a decompression device is engaged with the exhaust-side rocker arm and is mounted on the camshaft, a decompression shaft portion of a decompression cam which the decompression device includes is supported on an inner side of an outer peripheral surface of a base circle portion of the exhaust cam, and the decompression cam applies a decompression action to a projecting portion of an arm portion of the exhaust-side rocker arm. 
     
     
         17 . The rocker arm according to  claim 15 , wherein the arm portions of the exhaust-side rocker arm are formed wherein, compared to a width of the arm portion on a side where the arm portions is brought into contact with the decompression cam, a width of the arm portion on the other side is set small. 
     
     
         18 . The rocker arm according to  claim 14 , wherein the internal combustion engine is an internal combustion engine where the camshaft and the rocker shaft are arranged in front of a combustion chamber and in a planar projection view as viewed in the cylinder axis direction, with respect to each rocker arm, a size between an axis of the rocker shaft and an axis of the cam follower shaft is set smaller than a size between the axis of the rocker shaft and an axis of the camshaft. 
     
     
         19 . The structure of the rocker arm according to  claim 17 , wherein the rocker shaft is fixed to the cylinder head by fastening in a non-rotatable manner. 
     
     
         20 . The structure of the rocker arm according to  claim 13 , wherein the cam follower shaft of the cam follower is formed of a solid small-diameter shaft and a thickness of the outer ring in the radial direction is set smaller than a diameter of the roller.