Drive piston assembly for a valve actuator assembly

A valve actuator assembly for selectively opening a poppet valve, the valve actuator assembly comprising:

• a first valve in selective fluid communication with a source of fluid pressure;
• a drive piston assembly having:
• a cartridge defining a generally stepped bore;
• a drive piston movable within said generally stepped bore;
• a boost sleeve coaxially disposed with respect to said drive piston;
• a main fluid chamber at least partially defined by said generally stepped bore, drive piston, and boost sleeve;
• first and second feedback chambers at least partially defined by said drive piston and each disposed at opposite ends of said drive piston;
• wherein at least one of said drive piston and said boost sleeve is sufficiently configured to move within said generally stepped bore in response to fluid pressure within said main fluid chamber to selectively open the poppet valve;
• and
• wherein said first valve is operable to selectively and variably communicate fluid pressure to said main fluid chamber.

An internal combustion engine comprising:

• a cylinder head defining a port and at least partially defining a combustion chamber;
• a poppet valve operable to enable selective communication between said port and said combustion chamber;
• a valve actuator assembly operable to selectively open said poppet valve, said valve actuator assembly including;
• a first valve in selective fluid communication with a source of fluid pressure;
• a drive piston assembly having:
• a cartridge defining a generally stepped bore;
• a drive piston movable within said generally stepped bore;
• a boost sleeve coaxially disposed with respect to said drive piston;
• a main fluid chamber at least partially defined by said generally stepped bore, drive piston, and boost sleeve;
• first and second feedback chambers at least partially defined by said drive piston and each disposed at opposite ends of said drive piston;
• wherein at least one of said drive piston and said boost sleeve is sufficiently configured to move within said generally stepped bore in response to fluid pressure within said main fluid chamber to selectively open the poppet valve;
• wherein the drive piston includes a shoulder portion operable to engage said boost sleeve to enable unitary movement between said drive piston and said boost sleeve;
• wherein said generally stepped bore includes a land operable to selectively limit the movement of said boost sleeve within said generally stepped bore;
• and
• wherein said first valve is operable to selectively and variably communicate fluid pressure to said main fluid chamber.