Lost-motion variable valve actuation system

An actuation system, comprising:

• an autolash piston configured to slide within a housing to take up lash in a valve train to which the actuation system is coupled;
• a main valve disposed within the autolash piston and having a first position in which fluid is prevented from escaping from a lost-motion chamber formed in the autolash piston and a second position in which fluid is permitted to escape from the lost-motion chamber;
• a lost-motion piston that slides within the lost-motion chamber when the main valve moves from the first position to the second position, thereby allowing an engine valve to close;
• wherein the lost-motion piston progressively occludes a fluid path through which fluid escapes the lost-motion chamber when the main valve is in the second position.

A method of operating an engine that includes an engine valve actuated by a valve train, the method comprising:

• adjusting a position of an autolash piston relative to a housing in which the autolash piston is disposed to take up lash in the valve train, the autolash piston having a main valve chamber and a lost-motion chamber formed therein;
• opening a main valve disposed within the main valve chamber to permit fluid to escape from the lost-motion chamber, thereby allowing a lost-motion piston to slide within the lost-motion chamber to allow the engine valve to close;
• and
• progressively occluding a fluid path through which fluid escapes the lost-motion chamber with a portion of the lost-motion piston to control a seating velocity of the engine valve.

A valve train comprising:

• a cam having a cam surface;
• a rocker having a rocker pad surface;
• a bearing element having a cam-facing surface that slidably engages the cam surface and a rocker-facing surface that slidably engages the rocker pad surface;
• an actuation system configured to selectively permit the bearing element to be at least partially ejected from between the cam and the rocker;
• wherein:
• the cam surface has a substantially infinite widthwise radius of curvature;
• the cam-facing surface has a finite lengthwise radius of curvature and a substantially infinite widthwise radius of curvature;
• the rocker-facing surface has a finite lengthwise radius of curvature and a finite widthwise radius of curvature;
• and
• the rocker pad surface has a finite lengthwise radius of curvature and a finite widthwise radius of curvature.