Free piston engine system with direct drive hydraulic output

A free piston engine system, comprising:

• at least one hydraulic pump, each said pump having a first fluid port and a second fluid port;
• a free piston internal combustion engine including a combustion cylinder, a hydraulic cylinder, a piston reciprocally disposed within said combustion cylinder, and a plunger attached to said piston and disposed within said hydraulic cylinder;
• a low pressure accumulator fluidly coupled with said hydraulic cylinder;
• a first control valve interconnecting said low pressure accumulator with said hydraulic cylinder;
• at least one high pressure accumulator fluidly coupled with said hydraulic cylinder;
• at least one second control valve, each said second control valve interconnecting a respective said high pressure accumulator with said hydraulic cylinder, each said second control valve being a controllable electro-hydraulic poppet valve;
• a third control valve interconnecting said hydraulic cylinder with said first fluid port of each said pump;
• a fourth control valve interconnecting said hydraulic cylinder with said second fluid port of each said pump;
• and
• a first working pressure accumulator coupled between each said pump and one of said third control valve and said fourth control valve.

A free piston engine system, comprising:

• at least one hydraulic pump, each said pump having a first fluid port and a second fluid port;
• a free piston internal combustion engine including a combustion cylinder, a hydraulic cylinder, a piston reciprocally disposed within said combustion cylinder, and a plunger attached to said piston and disposed within said hydraulic cylinder;
• a low pressure accumulator fluidly coupled with said hydraulic cylinder;
• a first control valve interconnecting said low pressure accumulator with said hydraulic cylinder;
• at least one high pressure accumulator fluidly coupled with said hydraulic cylinder;
• at least one second control valve, each said second control valve interconnecting a respective said high pressure accumulator with said hydraulic cylinder;
• a third control valve interconnecting said hydraulic cylinder with said first fluid port of each said pump;
• a fourth control valve interconnecting said hydraulic cylinder with said second fluid port of each said pump, at least one of said third control valve and said fourth control valve being an electro-hydraulic spool valve;
• and
• a first working pressure accumulator coupled between each said pump and one of said third control valve and said fourth control valve.

A free piston engine system, comprising:

• at least one hydraulic pump, each said pump having a first fluid port and a second fluid port;
• a free piston internal combustion engine including a combustion cylinder, a hydraulic cylinder, a piston reciprocally disposed within said combustion cylinder, and a plunger attached to said piston and disposed within said hydraulic cylinder;
• a low pressure accumulator fluidly coupled with said hydraulic cylinder;
• a first control valve interconnecting said low pressure accumulator with said hydraulic cylinder;
• at least one high pressure accumulator fluidly coupled with said hydraulic cylinder;
• at least one second control valve, each said second control valve interconnecting a respective said high pressure accumulator with said hydraulic cylinder;
• a third control valve interconnecting said hydraulic cylinder with said first fluid port of each said pump;
• a fourth control valve interconnecting said hydraulic cylinder with said second fluid port of each said pump;
• a first working pressure accumulator coupled between each said pump and one of said third control valve and said fourth control valve;
• and
• a second working pressure accumulator coupled between each said pump and an other of said third control valve and said fourth control valve.

A work unit, comprising:

• at least one hydraulic pump, each said pump having a first fluid port and a second fluid port;
• a high pressure hydraulic source including a single hydraulic chamber associated therewith;
• a low pressure accumulator fluidly coupled with said single hydraulic chamber;
• a first control valve interconnecting said low pressure accumulator with said single hydraulic chamber;
• at least one high pressure accumulator fluidly coupled with said single hydraulic chamber;
• at least one second control valve, each said second control valve interconnecting a respective said high pressure accumulator with said single hydraulic chamber;
• a third control valve interconnecting said single hydraulic chamber with said first fluid port of each said pump;
• a fourth control valve interconnecting said single hydraulic chamber with said second fluid port of each said pump;
• and
• a first working pressure accumulator coupled between each said pump and one of said third control valve and said fourth control valve.

A method of operating a free piston engine system, comprising the steps of:

• providing at least one hydraulic pump, each said pump having a first fluid port and a second fluid port;
• providing a free piston internal combustion engine including a combustion cylinder, a hydraulic cylinder, a piston reciprocally disposed within said combustion cylinder, and a plunger attached to said piston and disposed within said hydraulic cylinder;
• fluidly coupling a first control valve between a low pressure accumulator and said hydraulic cylinder;
• fluidly coupling a second control valve between a high pressure accumulator and said hydraulic cylinder;
• fluidly coupling a third control valve between said hydraulic cylinder and said first fluid port of each said pump;
• fluidly coupling a fourth control valve between said hydraulic cylinder and said second fluid port of each said pump;
• coupling a first working pressure accumulator between each said PUMP and one of said third control valve and said fourth control valve;
• and
• selectively controlling said first control valve, said second control valve, said third control valve and said fourth control valve to drive at least one said pump in a closed flow path.