Valve Actuation Apparatus of Internal Combustion Engine and Rockable Cam for Use with the Same

Abstract

In a valve actuation apparatus of an internal combustion engine employing a motion converter for converting a rotary motion of a drive cam into an oscillating motion of a rockable cam, the rockable cam has a cam contour surface, for operating an engine valve by the oscillating motion. The cam contour surface is contoured to have a valve-opening small lift area through which the cam contour surface extends from a base-circle area, a valve-opening middle lift area extending continuously from the valve-opening small lift area toward a cam-nose portion, and a valve-opening large lift area extending continuously from the valve-opening middle lift area toward a cam-nose top. A radius of curvature ρ 2 of a part of the valve-opening middle lift area, bordering the valve-opening small lift area, is set to be less than a radius of curvature ρ 3 of the valve-opening large lift area.

1 . A valve actuation apparatus of an internal combustion engine comprising:
 a drive cam adapted to be linked to a crankshaft of the engine in a manner so as to be driven by a transmitted torque from the crankshaft;   a motion-transmission mechanism for converting a rotary motion of the drive cam into an oscillating motion; and   a rockable cam configured to move with an oscillating motion in synchronism with the oscillating motion produced by the motion-transmission mechanism and having a curved cam contour surface, for opening and closing an engine valve by the oscillating motion of the rockable cam,   wherein the cam contour surface of the rockable cam is contoured to have a valve-opening small lift area through which the cam contour surface extends from a base-circle area on which a lifter-crown contact surface rides when the engine valve is closed toward a cam-nose portion, a valve-opening middle lift area extending continuously from the valve-opening small lift area toward the cam-nose portion, and a valve-opening large lift area extending continuously from the valve-opening middle lift area toward a cam-nose top of the cam-nose portion, and   wherein a radius of curvature of a part of the valve-opening middle lift area, bordering the valve-opening small lift area, is set to be less than a radius of curvature of the valve-opening large lift area.   
     
     
         2 . The valve actuation apparatus as claimed in  claim 1 , wherein:
 the radius of curvature of the valve-opening large lift area is set to be less than a radius of curvature of the valve-opening small lift area.   
     
     
         3 . The valve actuation apparatus as claimed in  claim 1 , wherein:
 a radius of curvature of a part of the cam contour surface at which an acceleration of the oscillating motion of the rockable cam shifts from a positive acceleration area to a negative acceleration area, is set to be less than a radius of curvature of the base-circle area.   
     
     
         4 . The valve actuation apparatus as claimed in  claim 1 , wherein:
 the valve-opening small lift area is a positive acceleration area extending from a ramp area adjacent to the base-circle area; and   the valve-opening middle lift area and the valve-opening large lift area are a negative acceleration area after a last part of the positive acceleration area has passed the lifter-crown contact surface.   
     
     
         5 . A valve actuation apparatus of an internal combustion engine comprising:
 a drive cam adapted to be linked to a crankshaft of the engine in a manner so as to be driven by a transmitted torque from the crankshaft;   a motion-transmission mechanism for converting a rotary motion of the drive cam into an oscillating motion;   a rockable cam configured to move with an oscillating motion in synchronism with the oscillating motion produced by the motion-transmission mechanism and having a cam contour surface, for opening and closing an engine valve by the oscillating motion of the rockable cam;   a variator configured to vary a valve-lift amount of the engine valve by changing an attitude of the motion-transmission mechanism and consequently by changing a state of the oscillating motion of the rockable cam;   an actuator for driving the variator; and   a controller configured to control the actuator depending on an operating condition of the engine,   wherein the controller is configured to output a control signal to the actuator for bringing an operating characteristic of the engine valve closer to a maximum valve lift and maximum working angle characteristic via the variator during low-speed and low-load operation of the engine,   wherein the cam contour surface of the rockable cam is contoured to have a valve-opening small lift surface through which the cam contour surface extends from a base-circle surface on which a lifter-crown contact surface rides when the engine valve is closed via a ramp surface toward a cam-nose portion, a valve-opening middle lift surface extending continuously from the valve-opening small lift surface toward the cam-nose portion, and a valve-opening large lift surface extending continuously from the valve-opening middle lift surface toward a cam-nose top of the cam-nose portion, and   wherein a radius of curvature of a part of the valve-opening middle lift surface, bordering the valve-opening small lift surface, is set to be less than a radius of curvature of the valve-opening large lift surface, and the radius of curvature of the valve-opening large lift surface is set to be less than a radius of curvature of the valve-opening small lift surface.   
     
     
         6 . The valve actuation apparatus as claimed in  claim 5 , wherein:
 the low-speed and low-load operation comprises idling operation.   
     
     
         7 . The valve actuation apparatus as claimed in  claim 5 , wherein:
 the valve-opening small lift surface is a positive acceleration area extending from the ramp surface adjacent to the base-circle surface; and   the valve-opening middle lift surface and the valve-opening large lift surface are a negative acceleration area after a last part of the positive acceleration area has passed the lifter-crown contact surface.   
     
     
         8 . For use with a valve actuation apparatus of an internal combustion engine, a rockable cam comprising:
 a cam contour surface contoured to open and close an engine valve by an oscillating motion of the rockable cam,   wherein the cam contour surface is contoured to have a valve-opening small lift area through which the cam contour surface extends from a base-circle area on which a lifter-crown contact surface rides when the engine valve is closed toward a cam-nose portion, a valve-opening middle lift area extending continuously from the valve-opening small lift area toward the cam-nose portion, and a valve-opening large lift area extending continuously from the valve-opening middle lift area toward a cam-nose top of the cam-nose portion, and   wherein a radius of curvature of a part of the valve-opening middle lift area, bordering the valve-opening small lift area, is set to be less than a radius of curvature of the valve-opening large lift area.   
     
     
         9 . The rockable cam as claimed in  claim 8 , wherein:
 a radius of curvature of the valve-opening large lift area, extending continuously from the valve-opening middle lift area toward the cam-nose top, is set to be greater than the radius of curvature of a part of the valve-opening middle lift area, bordering the valve-opening small lift area.   
     
     
         10 . The rockable cam as claimed in  claim 8 , wherein:
 the valve-opening small lift area is a positive acceleration area extending from a ramp area adjacent to the base-circle area;   the valve-opening middle lift area and the valve-opening large lift area are a negative acceleration area after a last part of the positive acceleration area has passed the lifter-crown contact surface; and   the radius of curvature of the valve-opening large lift area of the negative acceleration area is set to be less than a radius of curvature of the base-circle area.