Design method of short duration cam, short duration cam, variable valve lift apparatus including the same, and design method of cam

Abstract

A short duration cam of a variable valve lift apparatus has a cam lift acceleration including a first peak formed before a center of the cam lift acceleration, and a second peak formed after the center of the cam lift acceleration. A relative ratio of a smaller value to a greater value of the first peak and the second peak is 0.8 or more.

What is claimed is: 
     
         1 . A method for manufacturing a short duration cam of a variable valve lift apparatus, the method comprising steps of:
 setting a cam lift acceleration of the short duration cam such that a first peak is formed before a center of the cam lift acceleration and a second peak is formed after the center of the cam lift acceleration; and   setting a curvature radius of a concave portion of the short duration cam based on the set cam lift such that a relative ratio of a smaller value to a greater value of the first peak and the second peak is 0.8 or more.   
     
     
         2 . The method of  claim 1 , wherein the short duration cam has a duration angle of 100 to 120 degrees between opening and closing of a valve comprising a ramp of the short duration cam. 
     
     
         3 . The method of  claim 1 , wherein the short duration cam has a valve lift profile to be asymmetrical based on a maximum valve lift of the short duration cam. 
     
     
         4 . A short duration cam of a variable valve lift apparatus, wherein a cam lift acceleration of the short duration cam has a first peak formed before a center of the cam lift acceleration and a second peak formed after the center of the cam lift acceleration, and a relative ratio of a smaller value to a greater value of the first peak and the second peak is 0.8 or more. 
     
     
         5 . The short duration cam of  claim 4 , wherein the short duration cam has a duration angle of 100 to 120 degrees between opening and closing of a valve including a ramp of the short duration cam. 
     
     
         6 . The short duration cam of  claim 4 , wherein the short duration cam has a valve lift profile to be asymmetrical based on maximum valve lift of the short duration cam. 
     
     
         7 . A variable valve lift apparatus comprising the short duration cam of  claim 4  and a long duration cam. 
     
     
         8 . The variable valve lift apparatus of  claim 7 , wherein the short duration cam is closed before reaching a bottom dead center. 
     
     
         9 . A method for manufacturing a cam, comprising:
 setting a cam lift acceleration of the cam such that a first peak is formed before a center of the cam lift acceleration and a second peak is formed after the center of the cam lift acceleration; and   setting a curvature radius of a concave portion of the cam based on the set cam lift such that a relative ratio of a smaller value to a greater value of the first peak and the second peak is 0.8 or more.   
     
     
         10 . The design method of  claim 9 , wherein the cam has a duration angle of 100 to 120 degrees between opening and closing of a valve including a ramp of the cam. 
     
     
         11 . The design method of  claim 9 , wherein the cam has a valve lift profile to be asymmetrical based on maximum valve lift of the cam.