Lost motion actuator with damping transition

Claim 1

A lost motion hydraulic actuator for use between a cam and a valve of an internal combustion engine and including a housing defining first and second oppositely opening coaxial cylinders, a first piston reciprocable in the first cylinder and defining a first chamber therein, a second piston reciprocable in the second cylinder and defining a second chamber therein, first biasing means urging the first piston axially outwardly toward operative connection with such cam, second biasing means urging the second piston axially outward toward operative connection with such valve, inlet means for admitting hydraulic fluid into said first chamber, a restrictive orifice continuously interconnecting said chambers for damping valve seating motion during valve closing, one way bypass flow means permitting flow around said orifice from said first chamber to said second chamber during valve opening, and secondary communication means between said chambers including a plurality of ports through said second cylinder and controlled by said second piston, said ports being open during valve lift beyond an initial amount for free flow of fluid between the chambers and said ports being closed by the piston prior to seating of the valve requiring flow from the second chamber to pass through said orifice for damping valve seating, the actuator being characterized in that: said ports and said second piston are configured to provide sequential closing of the ports during valve closing to limit the rate of change of fluid flow from the second chamber and provide a smooth transition to the inception of damping.