Piston and barrell assembly with stepped top and hydraulically-actuated fuel injector utilizing same

A hydraulically actuated piston and barrel assembly comprising:

• a barrel defining an actuation fluid cavity and a piston bore, which includes an upper bore and a lower bore;
• a piston with a stepped top being slidably received in said piston bore and moveable between a retracted position and an advanced position;
• said stepped top of said piston including a first area that is separate from a second area;
• said first area and said upper bore defining an upper cavity connected to said actuation fluid cavity through a relatively unrestricted flow area when said piston is in said retracted position;
• said second area and said lower bore defining a lower cavity connected to said actuation fluid cavity through a relatively restricted flow area when said piston is in said retracted position;
• said first area being exposed to fluid pressure in said upper cavity and said second area being exposed to fluid pressure in said lower cavity over a portion of said piston's movement from said retracted position toward said advanced position;
• and
• said stepped top of said piston defining a slot positioned in said upper bore when said piston is in said retracted position.

A hydraulically actuated fuel injector comprising:

• an injector body that includes a barrel and defines a plunger bore, a nozzle chamber and a nozzle outlet that opens to said nozzle chamber;
• a barrel defining an actuation fluid cavity and a piston bore, which includes an upper bore and a lower bore;
• a piston with a stepped top being slidably received in said piston bore and moveable between a retracted position and an advanced position;
• said stepped top of said piston including a first area that is separate from a second area;
• said first area and said upper bore defining an upper cavity connected to said actuation fluid cavity through a relatively unrestricted flow area when said piston is in said retracted position;
• said second area and said lower bore defining a lower cavity connected to said actuation fluid cavity through a relatively restricted flow area when said piston is in said retracted position;
• and
• said first area being exposed to fluid pressure in said upper cavity and said second area being exposed to fluid pressure in said lower cavity over a portion of said piston's movement from said retracted position toward said advanced position;
• one of said piston or said barrel further defining a restricted passage connecting said actuation fluid cavity to said lower cavity, and said restricted passage includes said restricted flow area;
• a plunger slidably positioned in said plunger bore;
• a portion of said plunger and said plunger bore defining a fuel pressurization chamber that opens to said nozzle chamber;
• a needle valve member positioned in said nozzle chamber and moveable between an open position in which said nozzle outlet is open and a closed position in which said nozzle outlet is blocked.

A hydraulically actuated fuel injector comprising:

• an injector body that includes a barrel and defines a plunger bore, a nozzle chamber and a nozzle outlet that opens to said nozzle chamber;
• a barrel defining an actuation fluid cavity and a piston bore, which includes an upper bore and a lower bore;
• a piston with a stepped top being slidably received in said piston bore and moveable between a retracted position and an advanced position;
• said stepped top of said piston including a first area that is separate from a second area;
• said first area and said upper bore defining an upper cavity connected to said actuation fluid cavity through a relatively unrestricted flow area when said piston is in said retracted position;
• said second area and said lower bore defining a lower cavity connected to said actuation fluid cavity through a relatively restricted flow area when said piston is in said retracted position;
• and
• said first area being exposed to fluid pressure in said upper cavity and said second area being exposed to fluid pressure in said lower cavity over a portion of said piston's movement from said retracted position toward said advanced position;
• said stepped top of said piston defining a slot positioned in said upper bore when said piston is in said retracted position;
• a plunger slidably positioned in said plunger bore;
• a portion of said plunger and said plunger bore defining a fuel pressurization chamber that opens to said nozzle chamber;
• a needle valve member positioned in said nozzle chamber and moveable between an open position in which said nozzle outlet is open and a closed position in which said nozzle outlet is blocked.

A hydraulically actuated fuel injector comprising:

• an injector body that includes a barrel and defines a nozzle chamber, a needle control chamber and a nozzle outlet that opens to said nozzle chamber;
• a barrel defining an actuation fluid cavity and a piston bore, which includes an upper bore and a lower bore;
• hydraulic means, within said injector body for pressurizing fuel in said nozzle chamber, said hydraulic means including a piston with a stepped top being slidably received in said piston bore and moveable between a retracted position and an advanced position;
• said stepped top of said piston including a first area that is separate from a second area;
• said first area and said upper bore defining an upper cavity connected to said actuation fluid cavity through a relatively unrestricted flow area when said piston is in said retracted position;
• said second area and said lower bore defining a lower cavity connected to said actuation fluid cavity through a relatively restricted flow area when said piston is in said retracted position;
• and
• said first area being exposed to fluid pressure in said upper cavity and said second area being exposed to fluid pressure in said lower cavity over a portion of said piston's movement from said retracted position toward said advanced position;
• a needle valve member positioned in said nozzle chamber and moveable between an open position in which said nozzle outlet is open and a closed position in which said nozzle outlet is blocked, and said needle valve member including a closing hydraulic surface exposed to pressure in said needle control chamber;
• and
• a needle control valve attached to said injector body and being moveable between an off position in which said needle control chamber is opened to a source of high pressure fluid and an on position in which said needle control chamber is opened to a low pressure passage.