Fully-controlled, free-piston engine

A method of operating a free-piston engine having at least one engine unit, the engine unit including a pair of axially opposed combustion cylinders respectively housing free-floating combustion pistons therein, wherein each combustion piston has at least one pumping piston fixed thereto and mounted in a hydraulic cylinder for reciprocating linear motion therein and wherein the combustion pistons are fixed together and reciprocate in tandem as a dual piston assembly, said method comprising:

• drawing a fluid at a low pressure, through a low pressure fluid intake valve, into the hydraulic cylinders as the pumping pistons travel from BDC to TDC and discharging the fluid at a high pressure, higher than the low pressure, as the pumping pistons travel from TDC to BDC;
• reading position indicators on the dual piston assembly to generate position signals for a power stroke in one direction;
• measuring said high pressure and said low pressure and generating pressure signals representative of the measured pressures;
• determining, on the basis of said position signals and said pressure signals, position for closing the low pressure fluid intake valve in the same stroke, to cause the dual piston assembly to stop at the commanded stoppage position and to thereby extract hydraulic power and achieve the target compression ratio of the opposite combustion piston in real time, in the same stroke.

A method of operating a free-piston engine having at least one engine unit including a pair of axially opposed combustion cylinders respectively housing free-floating combustion pistons therein, wherein each combustion piston has at least one pumping piston fixed thereto and mounted in a hydraulic cylinder for reciprocating linear motion therein and wherein the paired combustion pistons are fixed together and reciprocate in tandem as a dual piston assembly, said method comprising:

• drawing a fluid at a low pressure, through a low pressure fluid intake valve, into the hydraulic cylinders as the pumping pistons travel from BDC to TDC and discharging the fluid at a high pressure, higher than the low pressure, as the pumping pistons travel from TDC to BDC;
• reading position indicators, located on the dual piston assembly at plural positions of the dual piston assembly, in a power stroke of a given cycle to generate position signals;
• determining energy produced by a single combustion event in said given cycle, as a function of the velocity and acceleration of the dual piston assembly, on the basis of the position signals;
• measuring said high pressure and said low pressure and generating pressure signals representative of the measured pressures;
• on the basis of the determined energy and said pressure signals, determining a position for closing the low pressure fluid intake valve for attaining a target compression ratio for a compression stroke in a cycle subsequent to said given cycle;
• and
• in said given cycle, closing the low pressure fluid intake valve during discharge back to low pressure to cause the dual piston assembly to stop at the desired stoppage position to thereby achieve the target compression ratio in real time.

A free-piston engine comprising:

• a pair of parallel side-by-side combustion cylinders;
• a free-floating combustion piston mounted in each of said combustion cylinders for reciprocating linear motion therein, responsive to successive combustion events within said combustion cylinders;
• at least one pumping piston extending from and fixed to each of said combustion pistons;
• a hydraulic cylinder receiving each of said pumping pistons for reciprocating motion therein;
• a shuttle cylinder axially aligned with and in fluid communication with each of said hydraulic cylinders and a shuttle piston mounted in each shuttle cylinder for reciprocating motion therein;
• connectors for rigidly and axially connecting each shuttle piston to a pumping piston;
• a transfer tube providing fluid communication respectively between said shuttle cylinders;
• and
• a flexible linkage passing through said transfer tube and connecting the shuttle pistons.

A free-piston engine comprising:

• four parallel side-by-side combustion cylinders;
• a free-floating combustion piston mounted in each of said combustion cylinders for reciprocating linear motion therein, responsive to successive combustion events within said combustion cylinders;
• at least one pumping piston extending from and fixed to each of said combustion pistons;
• a hydraulic cylinder receiving each of said pumping pistons for reciprocating motion therein;
• a shuttle cylinder axially aligned with and in fluid communication with each of said hydraulic cylinders and a shuttle piston mounted in each shuttle cylinder for reciprocating motion therein;
• connectors for rigidly and axially connecting a shuttle piston to each pumping piston;
• transfer tubes providing fluid communication respectively between first and second shuttle cylinders and between third and fourth shuttle cylinders;
• flexible linkages passing through respective transfer tubes and connecting, respectively the shuttle pistons in the first and second shuttle cylinders and the shuttle pistons in the third and fourth shuttle cylinders;
• and
• a linkage connecting together the shuttle pistons in the second and third shuttle cylinders for movement together in tandem along with associated pumping pistons and combustion pistons.

A method of operating a free-piston engine having at least one engine unit, the engine unit including a pair of axially opposed combustion cylinders respectively housing free-floating combustion pistons therein, wherein each combustion piston has at least one pumping piston fixed thereto and mounted in a hydraulic cylinder for reciprocating linear motion therein and wherein the combustion pistons are fixed together and reciprocate in tandem as a dual piston assembly, said method comprising:

• drawing a fluid at a low pressure, through a low pressure fluid intake valve, into the hydraulic cylinders as the pumping pistons travel from BDC to TDC and discharging the fluid at a high pressure, higher than the low pressure, as the pumping pistons travel from TDC to BDC;
• determining fuel energy commanded for a power stroke in one direction;
• measuring said high pressure and said low pressure and generating pressure signals representative of the measured pressures;
• measuring engine temperature and generating temperature signals representative of the measured temperature;
• determining expected cycle efficiency from tables or algorithms, on the basis of the temperature signals and the determined fuel energy commanded;
• and
• determining, on the basis of said fuel energy commanded, said pressure signals and said expected cycle efficiency, a position for closing the low pressure fluid intake valve in the same stroke, to cause the dual piston assembly to stop at the commanded stoppage position and to thereby extract hydraulic power and achieve the target compression ratio of the opposite combustion piston in the same stroke.

A method of operating a free-piston engine having at least two engine units, each engine unit including two axially opposed combustion cylinders respectively housing free-floating combustion pistons therein, wherein each combustion piston has at least one pumping piston fixed thereto and mounted in a hydraulic cylinder for reciprocating linear motion therein, wherein the two combustion pistons are fixed together and reciprocate in tandem as a dual piston assembly and wherein the two combustion pistons of a first engine unit are connected to the two combustion pistons of a second engine unit for synchronized movement in opposite directions, said method comprising:

• drawing a fluid at a low pressure, through a low pressure fluid intake valve, into the hydraulic cylinder of a first pumping piston during an exhaust stroke of a first combustion piston, fixed to said first pumping piston;
• drawing an air charge into the combustion cylinder housing of said first combustion piston by an intake stroke of said first combustion piston, while keeping open said low pressure fluid intake valve and discharging fluid from the hydraulic cylinder of said first pumping piston at the low pressure;
• compressing the air charge by a compression stroke of said first combustion piston while drawing fluid back into the hydraulic cylinder of the first pumping piston;
• closing the low pressure fluid intake valve and discharging fluid from the hydraulic cylinder of the first pumping piston at a high pressure, higher than the low pressure, while the first combustion piston goes through a power stroke;
• reading position indicators on a dual piston assembly including said first combustion piston to generate position signals for one of said strokes in one direction;
• and
• determining, on the basis of the position signals, a position for closing the low pressure fluid intake valve in the same cycle to extract hydraulic power and achieve a target compression ratio in real time, in the compression stroke of a second combustion piston, paired with the first combustion piston.

A method of operating a free-piston engine having at least two engine units, each engine unit including two axially opposed combustion cylinders respectively housing free-floating combustion pistons therein, wherein at least two of said combustion pistons have at least one pumping piston fixed thereto and mounted in a hydraulic cylinder for reciprocating linear motion therein, wherein the two combustion pistons are fixed together and reciprocate in tandem as a dual piston assembly and wherein the two combustion pistons of a first engine unit are connected to the two combustion pistons of a second engine unit for synchronized movement in opposite directions, said method comprising:

• drawing a fluid at a low pressure, through a low pressure fluid intake valve, into the hydraulic cylinder of a first pumping piston during a first stroke to top dead center of a first combustion piston, fixed to said first pumping piston;
• closing the low pressure fluid intake valve and discharging fluid from the hydraulic cylinder of the first pumping piston at a high pressure, higher than the low pressure, while the first combustion piston goes through a power stroke;
• drawing a fluid at low pressure, through a low pressure fluid intake valve, into the hydraulic cylinder of said first pumping piston during a second stroke to top dead center of said first combustion piston;
• closing the low pressure fluid intake valve and discharging fluid from the hydraulic cylinder of said first pumping piston at a high pressure, higher than the low pressure, while a second combustion piston, fixed to said first combustion piston in a dual piston assembly, goes through a power stroke;
• reading position indicators on a dual piston assembly including said first combustion piston to generate position signals for one of said strokes in one direction;
• and
• determining, on the basis of the position signals, a position for closing the low pressure fluid intake valve in the same cycle to extract hydraulic power and achieve a target compression ratio in real time, in the compression stroke of said second combustion piston.