Method and apparatus for starting a free piston combustion engine hydraulically

• US 5,123,245 A
• Filed: 10/21/1991
• Issued: 06/23/1992
• Est. Priority Date: 10/19/1990
• Status: Expired due to Fees

• Current Assignee: Sampower OY
• Original Assignee: Sampower OY
• Inventors: Vilenius, Matti, Koskinen, Kari, Lehto, Erkki, Huhtala, Kalevi
• Primary Examiner(s): Ostrager, Allen M.
• Application Number:
  US07/780,040
• Time in Patent Office: 246 Days
• Field of Search: 60/596
• US Class Current: 60/596
• CPC Class Codes: F02B 71/02 Starting
• CPC Class Codes: F02B 71/045 with hydrostatic transmission

Abstract

A method of starting a free piston combustion engine is described in which the free piston unit consisting of the combustion pistons and the piston rod connecting them is set in motion by alternately pressurizing the hydraulic cylinder spaces of a double-acting piston and cylinder arrangement whose piston or piston is or are connected to the piston rod. For this purpose pressure from a hydraulic accumulator used for starting the engine is supplied as a control pressure to the check valve members of the one way outlet check valves of the hydraulic cylinder spaces to keep those check valves closed during starting of the engine. This control pressure supplements the spring pressure supplied by springs in the check valves biasing the check valve members towards their closed positions. Simultaneously a directional valve is used to channel hydraulic fluid from the hydraulic accumulator directly to the cylinder spaces in turn, thereby bypassing the one way inlet check valves to the cylinder spaces. In this way the free piston unit is set in motion. Once the free piston has performed a predetermined number of reciprocating movements or has attained a sufficient magnitude of inertial energy the hydraulic accumulator is disconnected so that the inlet and outlet valves can perform their normal function, while simultaneously or just before or just after this moment fuel combustion is initiated to maintain the engine in operation. An electronic controller responsive to signals from sensors mounted on the engine from which can be derived information about the position and speed of the free piston unit can be used to control starting and operation of the engine.

Claims

1. A free piston combustion engine comprising:

body means defining a pair of opposed combustion cylinders;

a combustion piston reciprocably disposed in each said combustion cylinder for reciprocal motion therein;

piston rod means connecting said combustion pistons one to another whereby said combustion pistons may reciprocate in unison in their respective combustion cylinders;

hydraulic power output means including at least one pair of hydraulic cylinder spaces having an associated hydraulic piston reciprocably disposed therein, said hydraulic piston being operatively linked to said piston rod so as to reciprocate in unison therewith;

hydraulic accumulator means for storage of hydraulic fluid under elevated pressure for use in starting said engine;

hydraulic inlet check valves for controlling inlet of hydraulic fluid to each said hydraulic cylinder space, said hydraulic inlet check valves each including a first check valve member movable between a first position in which it permits inlet of hydraulic fluid to its respective hydraulic cylinder and a second position in which it prevents inlet of hydraulic fluid thereto;

first hydraulic control means connected between said hydraulic accumulator means and said hydraulic cylinder spaces for controlling flow of hydraulic fluid from said hydraulic accumulator means to said hydraulic cylinder spaces during starting of said engine, said first hydraulic control means including a directional valve means permitting, in one condition thereof, inlet of hydraulic fluid from said hydraulic accumulator means to one of a respective pair of hydraulic cylinder spaces and outlet of hydraulic fluid from the other one thereof and permitting, in another condition of said directional valve means, inlet of hydraulic fluid from said hydraulic accumulator means to said other hydraulic cylinder space of said pair and outlet of hydraulic fluid from said one hydraulic cylinder space of said pair;

hydraulic outlet check valves for controlling outlet of hydraulic fluid from each said hydraulic cylinder space, said hydraulic outlet check valves each including a second check valve member movable between a first position in which it permits outlet of hydraulic fluid from its respective hydraulic cylinder space to an output supply line and a second position in which it prevents outlet of hydraulic fluid from its respective hydraulic cylinder space; and

second hydraulic control means connected between said hydraulic accumulator means and said hydraulic outlet check valves arranged to permit application of an elevated control pressure to said second check valve members so as to move them each to its respective said second position to prevent outlet of hydraulic fluid from its associated hydraulic cylinder space during starting of said engine so long as the pressure within said associated hydraulic cylinder space does not exceed said elevated control pressure;

said first hydraulic control means being arranged to permit, during starting of said engine, by repeated switching of said directional valve means between said first and second conditions thereof, hydraulic fluid to enter each of said pair of hydraulic cylinder spaces in turn from said hydraulic accumulator means thereby to impart reciprocal motion to said piston rod and to said combustion pistons so as to produce in said combustion cylinders in turn a desired compression pressure at which combustion can be initiated therein; and

said second hydraulic control means being arranged so that, at a predetermined moment after said piston rod together with said pistons begins to reciprocate, said control pressure is removed from said second check valve members to permit outlet of hydraulic fluid from said hydraulic cylinder spaces.

2. A free piston combustion engine according to claim 1, wherein said hydraulic power output means comprises a double-acting piston and cylinder arrangement including a single piston slidable within a common cylinder and dividing said common cylinder into said pair of opposed said hydraulic cylinder spaces.

3. A free piston combustion engine according to claim 1, wherein said hydraulic power output means comprises a pair of single-acting piston/cylinder pumps in a boxer arrangement.

4. A free piston combustion engine according to claim 1, wherein said second hydraulic control means includes a control valve having a first inlet connected to said hydraulic accumulator means, a second inlet connected to said output supply line, and an outlet connected to said hydraulic outlet check valves, said control valve including a check valve member movable between a first end position in which it permits communication between said first inlet and said outlet to permit application of hydraulic pressure from the hydraulic accumulator means to said second check valve members to bias them towards their respective second positions and a second end position in which it permits communication between said second inlet and said outlet to permit the pressure on the two sides of the said second check valve members substantially to equalise to permit free movement thereof between their respective said first and second positions.

5. A free piston combustion engine according to claim 4, wherein each said hydraulic outlet check valve further comprises spring means resiliently biasing said second check valve member towards its second position whereby said control pressure is provided by a combination of hydraulic pressure from said hydraulic accumulator means and spring pressure provided by said spring means.

6. A free piston combustion engine according to claim 1, wherein said output supply line is provided with a hydraulic motor arranged to drive an electric generator and a flushing pump.

7. A free piston combustion engine according to claim 1, wherein said first hydraulic control means and said second hydraulic control means are under the control of an electronic controller which is connected to sensors arranged to sense the speed and position of said free piston unit.

8. A free piston combustion engine according to claim 7 wherein said electronic controller is arranged to initiate fuel injection at a moment which is selected from the moment at which said free piston unit has completed a preset number of reciprocating movements and the moment at which said free piston unit has attained a predetermined magnitude of inertial energy and wherein said electronic controller is arranged to disable said first hydraulic control means and stop switching of said directional valve means between its first and second positions at a second moment selected from said first moment, a moment immediately before said first moment, and a moment immediately after said first moment, thereby to permit said hydraulic cylinder spaces to receive hydraulic fluid via said hydraulic inlet check valve means from a reservoir for hydraulic fluid.

9. A free piston combustion engine according to claim 1, wherein a further pressure accumulator means is connected to said output supply means and wherein said hydraulic accumulator means can be pressurized to a higher pressure than the pressure in said further pressure accumulator means.

10. An internal combustion assisted hydraulic engine comprising:

body means defining a pair of opposed combustion chambers;

a combustion piston reciprocably disposed in each said combustion chamber for reciprocal motion therein;

a piston rod rigidly connecting said combustion pistons to cause said combustion pistons to reciprocate in their respective combustion chambers in unison with said piston rod as a free piston unit;

at least one double-acting hydraulic pump comprising a pair of hydraulic cylinder spaces with a hydraulic piston reciprocably disposed therein, said hydraulic piston or pistons being operatively connected to said piston rod to move in unison therewith;

a reservoir for hydraulic fluid;

an output pressure line for supply of hydraulic fluid under pressure to a hydraulic actuator;

hydraulic accumulator means for storage of hydraulic fluid under pressure for starting said engine;

hydraulic inlet check valves for controlling inlet of hydraulic fluid to said hydraulic cylinder spaces, each said hydraulic inlet check valve including a first check valve member movable between a first position in which it permits inlet to its respective cylinder space of hydraulic fluid from said reservoir and a second position in which it prevents inlet of hydraulic fluid to its respective hydraulic cylinder space;

hydraulic outlet check valves for controlling outlet of hydraulic fluid from said hydraulic cylinder spaces, each said hydraulic outlet check valve including a second check valve member movable between a first position in which it permits outlet of hydraulic fluid from its respective hydraulic cylinder space to said output pressure line, and a second position in which it prevents outlet of respective hydraulic fluid from said hydraulic cylinder space to said output pressure line;

first hydraulic control means connected between said hydraulic accumulator means and said hydraulic cylinder spaces and including a directional valve means permitting, in one condition thereof, inlet of hydraulic fluid from said hydraulic accumulator means to one hydraulic cylinder space of the or a said pair of hydraulic cylinder spaces and outlet of hydraulic fluid from the other hydraulic cylinder space of the respective pair of hydraulic cylinder spaces to said reservoir and, in another condition thereof, outlet of hydraulic fluid from said one hydraulic cylinder space to said reservoir and inlet of hydraulic fluid to said other hydraulic cylinder space from said hydraulic accumulator means; and

second hydraulic control means for applying, during starting of said engine, a hydraulic control pressure to said second check valve members to bias them each towards its respective second position to prevent outlet of hydraulic fluid from its associated hydraulic cylinder space to said output pressure line so long as the pressure biasing said second check valve members towards their respective second positions exceeds the pressure within said associated hydraulic cylinder space;

said first hydraulic control means being arranged so that, during starting of said engine, said directional valve means is repeatedly switched between its first and second positions to pressurize the hydraulic cylinder spaces of the or each said pair of hydraulic cylinder spaces in turn thereby to cause reciprocation of said free piston unit until a desired compression pressure has been achieved in a respective said combustion chamber sufficient to permit initiation of the combustion process therein; and

said second hydraulic control means being arranged so that, at a desired instant after said piston unit begins to reciprocate, said hydraulic control pressure is released to permit hydraulic fluid to flow from said hydraulic cylinder spaces to said output pressure line.

11. An internal combustion assisted hydraulic engine according to claim 10, wherein said double-acting hydraulic pump means comprises a piston movable within a common cylinder and dividing said common cylinder into a pair of hydraulic cylinder spaces.

12. An internal combustion assisted hydraulic engine according to claim 10, wherein said at least one double-acting hydraulic pump means comprises a twin set of single-acting piston/cylinder pumps in a boxer arrangement.

13. An internal combustion assisted hydraulic engine according to claim 10, wherein said output pressure line is provided with a low power hydraulic motor arranged to drive an electric generator and a flushing pump.

14. An internal combustion assisted hydraulic engine according to claim 10, wherein said first hydraulic control means and said second hydraulic control means are arranged to be controllable by an electronic controller which is connected to sensors sensing the speed and position of free piston unit.

15. An internal combustion assisted hydraulic engine according to claim 10, wherein said electronic controller is arranged to initiate fuel injection at a first instant which is selected from the instant at which said free piston unit has completed a preset number of reciprocating movements and the instant at which said free piston unit has attained a predetermined magnitude of an inertial energy, said electronic controller further being arranged to disable said first hydraulic control means at a second instant which is selected from said first instant, an instant immediately before said first instant, and an instant immediately after said first instant, thereby to permit hydraulic fluid to be drawn from said reservoir into said hydraulic cylinder spaces via said hydraulic inlet check valves.

16. An internal combustion assisted hydraulic engine according to claim 10, wherein a pressure accumulator means is connected to said output pressure line, said hydraulic accumulator means being arranged to be pressurized to a higher pressure than said pressure accumulator means.

17. An internal combustion assisted hydraulic engine according to claim 10, wherein said second hydraulic control means includes a control valve having a first inlet which can be placed in fluid communication with said hydraulic accumulator means, a second inlet in fluid communication with said output supply line, and an outlet in fluid communication with said hydraulic outlet check valves, said control valve including a check valve member movable between a first control position in which it permits fluid communication between said first inlet and said outlet to permit application of hydraulic pressure from said hydraulic accumulator means to said second check valve members to bias them towards their respective second positions and a second control position in which it permits communication between said second inlet and said outlet to permit the pressure on the two sides of said second check valve members to equalise to permit free movement thereof between their respective first and second positions and wherein said hydraulic control means further includes means for interrupting communication between said hydraulic accumulator means and said first inlet.

18. An internal combustion assisted hydraulic engine according to claim 17, wherein each said hydraulic outlet check valve further comprises spring means resiliently biasing said second check valve member towards its second position whereby said pressure biasing said second check valve member towards its second position during starting of said engine comprises the sum of said hydraulic control pressure and spring pressure provided by said spring means.

19. A method of starting an internal combustion assisted hydraulic engine having a pair of opposed combustion chambers, a combustion piston reciprocably disposed in each said combustion chamber and linked one to another by a piston rod to form a free piston unit, at least one double-acting hydraulic pump comprising a pair of hydraulic cylinder spaces with a hydraulic piston reciprocably disposed therein, said hydraulic piston or pistons being operatively connected to said piston rod to move in unison therewith, one way inlet check valves for controlling inlet of hydraulic fluid from a reservoir to said hydraulic cylinder spaces, one way outlet check valves for controlling outlet of hydraulic fluid from said hydraulic cylinder spaces, each said one way valve including a check valve member movable under the influence of a control pressure applied thereto between a first end position permitting flow of hydraulic fluid through said check valve and a second position preventing flow of hydraulic fluid through said check valve, said method comprising the steps of:

providing a hydraulic accumulator means pressurized to an elevated pressure for starting said engine;

connecting said hydraulic accumulator means to said one way outlet check valves so as to apply the pressure prevailing in said hydraulic accumulator means as an elevated hydraulic control pressure to said check valve members thereof to close said one way outlet control valves;

supplying hydraulic fluid from said hydraulic accumulator means to each of said hydraulic cylinder spaces of the or a said respective pair of said hydraulic cylinder spaces in turn thereby to pressurize said hydraulic cylinder spaces in turn and to impart a reciprocating motion to said free piston unit; and

disconnecting said hydraulic accumulator means from said one-way outlet check valves so as to remove the elevated hydraulic control pressure from said check valve members thereof thereby to permit opening of said one way outlet check valves at a moment selected from a first moment at which the combustion process is initiated, a second moment immediately preceding said first moment, and a third moment immediately following said first moment.

20. A method according to claim 19, wherein closure of said one-way outlet check valves is assisted by application of spring pressure from spring means arranged to bias said respective check valve members towards their closed positions.

21. A method according to claim 19, wherein the step of alternatively pressurizing said hydraulic cylinder spaces includes the step of switching a directional valve between end positions permitting flow of hydraulic fluid into one said cylinder hydraulic space and out from the other said hydraulic cylinder space of the or a said pair of hydraulic cylinder spaces while said piston unit is moving in one direction and allowing inlet of hydraulic fluid to said other hydraulic cylinder space and outlet of hydraulic fluid from said one hydraulic cylinder space when said piston unit is moving in the other direction, switching of said directional valve being under control of an electronic controller in dependence upon information about the position and speed of said free piston unit derived by said controller from signals from sensors mounted in the engine.

22. A method according to claim 19, wherein initiation of the combustion process in said combustion chambers is effected after a first predetermined time from initiating starting of said engine, said predetermined time being selected from a time period required for said free piston unit to complete a preset number of reciprocating movements and a time period sufficient for the free piston to attain a predetermined magnitude of inertial energy, and wherein, after a second predetermined time from initiation of the starting procedure, said second time being selected from said first predetermined time, a time interval slightly shorter than said first predetermined time, and a time period slightly longer than said first predetermined time, the step of alternately pressurizing said hydraulic cylinder spaces from said hydraulic accumulator means is terminated, thereby allowing hydraulic fluid to be drawn from said reservoir into said hydraulic cylinder spaces via said one-way inlet check valves.