US3386647A - Free-piston engine diaphragm compressor - Google Patents

Description

June 4, 1968 s. E. SORENSEN ET AL 3,386,647

FREE-PISTON ENGINE DIAPHRAGM COMPRESSOR Filed Oct. 22, 1965 5 Sheets-Sheet l o SVEND E. SORENSEN e 0 WILLIAM L. McHALE Fig. l mvsmons June 4, 1968 SORENSEN ET AL 3,386,647

FREE-PISTON ENGINE DIAPHRAGM COMPRESSOR Filed Oct. 22, 1965 5 Sheets-Sheet 2 svsuo E. SORENSEN 3 WILLIAM L. McHALE INVEN TORS BY 4 7., m M QM W June 4, 1968 s. E. SORENSEN ET 3,386,647

FHEEPISTON ENGINE DIAPHRAGM COMPRESSOR Filed Oct. 22, 1965 5 Sheets-Sheet 3 Fig. 4

SVEND E. SORENSEN WILLIAM L. McHALE INVEN'TORS BY ,ufmw Q June 4, 1968 Filed Oct. 22, 1965 S. E. SORENSEN ET FREE-PISTON ENGINE DIAPHRAGM COMPRESSOR 5 Sheets-Sheet 4 RELAY NO. I

THERMOSTAT POWER SUPPLY SPARK GEN.

CONDENSOR /363 FAN EVAPORATOR V BLOWER ENGINE LUBE /367 MOTOR ENGINE COOLING /369 was BLOWER 29l AIR TANK {RELAY SOLENOID o 2 3 WAY VALVE I579 SOLENOID \293 Fig. 9

CAM SWITCH RELAY 377 37l (VIBRATION 0R PRESSURE SWITCH SVEND E. SORENSEN WILLIAM L. McHALE INVENTORS June 4, 1968 s. E. SORENSEN ET 3,336,647

FREEPISTON ENGINE DIAPHRAGM COMPRESSOR 5 Sheets-Sheet 5 Filed Oct. 22, 1965 STORAGE TANK 283 souswow zal h VALVE CHECK 385 VALVE TAP-OFF VALVE SOLENOID m VALVE CONDENSOR EVAPORATOR DEVICE Fig.

N m 8 A N H H c 0 M L M mm u S M 5 m man wmw ww 3 I a 1/ i I m m M W B 3 3 2 .W F E 3 United States Patent 3,386,647 FREE-PISTON ENGINE DIAPHRAGM COMPRESSOR Svend E. Sorensen, King of Prussia, and William L. Mc-

Hale, Broomall, Pa., assignors, by mesne assignments, to

The Battelle Development Corporation, Columbus,

Ohio, a corporation of Delaware Filed Get. 22, 1965, Ser. No. 501,719 Claims. (Cl. 23049) ABSTRACT OF THE DISCLOSURE This invention concerns a compressor which includes a free-piston engine wherein the free-piston is connected by a piston rod to a working piston. The working piston reciprocates against a column of oil that in turn flexes a diaphragm. The reciprocations of the diaphragm compress a gas so that the apparatus is useful as a refrigeration system. Other features include: an ignition system that is triggered by the reciprocation of the pistons, overstroke control of the free-piston by automatically adding to the column of oil, a starting system based on storage of high pressure combustion gas, and a vibration sensing device that shuts olf the starting system after the engine starts.

This invention relates to a compressor. More particularly, the invention concerns a free-piston engine, diaphragm compressor that is especially useful in a refrigeration system.

Briefly, this invention includes a free-piston engine that transmits energy to the diaphragm of a diaphragm compressor through an oil column. The diaphragm compressor provides a portion of the rebound energy for the free piston and other element-s are provided that serve both the free-piston engine and the compressor to make the engine and compressor so interdependent and closely linked that they are essentially an integral unit.

One of the many problems of refrigerant compressors is sealing. Some movement of the usual compressor, either rotating or reciprocating, is required to compress the refrigerant gas. As a result there is customarily a seal of some sort involved in separating the power source from the compressor. This is especially true where the power source is, as it is in this invention, an internalcombustion engine. The sealing problem is greatly reduced, in this invention, from that of a dynamic seal to essentially a static seal, i.e., at a portion adjacent to the periphery of the diaphragm, by the diaphragm compressor.

Many electrically powered compressors are hermetically sealed with the power source enclosed in the system and acting in the atmosphere of the refrigerant. These systems also have problems since the sealed-in moving parts require lubrication. The oil in the refrigerant system has a tendency to coat and thereby insulate important heat transfer surfaces reducing the efficiency of the system. The oil contamination problem is also eliminated in this invention by use of the diaphragm compressor. The oil column of this invention, which provides for the transfer of energy from the power source to the compressor, also provides lubrication for some of the moving parts of the power source.

An important advantage of the free-piston-engine diaphragm compressor is the reduction in Weight and noise as compared to other refrigeration systems that must change rotary motion to reciprocating motion. In this invention, the engine motion and compressor motion are both reciprocating so that there is also a cost savings by 3,386,647 Patented June 4, 1968 the elimination of motion changing linkages and complicated force transfer apparatus.

It is an object of this invention to provide a refrigeration compressor driven by a free-piston engine that is capable of automatic operation including starting and stopping and that is especially useful for residential and similar installations.

It is another object of this invention to eliminate many of the parasitic features common to many conventional compressors such as excess friction, leakage, extra gadgets, complicated starting mechanisms, etc.

Still another object of this invention is to provide a dependable engine wherein carburetion and ignition are constructed to give reliable operation. The carburetion is accomplished by a construction that uses pressure changes from piston motion to supply the fuel already mixed with the air to the engine cylinder. The ignition system is a solid state ignition system that senses the piston position to fire the spark plug at precisely the right moment. The piston movement triggers a pick-up device by breaking a magnetic flux path to supply an input sig nal to a circuit (preferably transistorized) for producing a spark in the combustion cylinder. This is accomplished without the need for mechanical connection between the piston assembly and the ignition pick-up device. A particular orientation of the piston assembly is therefore not required. The ignition system of this invention does not depend upon breaker points, cam follower mechanisms or other moving parts (except the piston assembly) and consequently can operate for extremely long periods of time without replacement of parts.

Still another object of this invention is to provide a construction wherein the alignment problem for the reciprocating parts of the free-piston engine are largely eliminated.

Still another object of this invention is to provide a construction whereby the stroke-length of the piston assembly is held within close limits under all conditions of operation.

Still another object of this invention is to provide a construction whereby loss of refrigerant is virtually eliminated since an intermediate fluid (hydraulic) acting on the diaphragm performs the force transfer function between the engine and the compressor.

A still further object of this invention is to provide a construction whereby the unit is cycled at least once before an attempt is made to energize the ignition, such action effectively purging the engine thereby providing the starting reliability requiried.

A still further object of this invention is to provide a construction whereby the energy required for starting is generated during operation of the unit.

Still another object of the invention is to provide a detector that signals the starting system when the unit is running.

Still other objects and advantages of the invention will be apparent from the detailed description of the process and apparatus, the drawings and the claims that follow.

In the drawings:

FIG. 1 is a sectional elevational view of the free-pistonengine diaphragm compressor.

FIG. 2 is a plan view of the compressor diaphragm back-up plate.

FIG. 3 is a plan view of the compressor valve plate.

FIG. 4 is a sectional elevational view of the oil pump used for supplying oil to the oil coupling between the free-piston engine and the diaphragm of the compressor section.

FIG. 5 is a sectional view of the ignition pick-up that triggers the high-tension circuit for firing the free-piston engine spark plug at the proper time.

FIG. 6 is a diagram of the high-tensioin circuit for firing the spark plug.

FIG. 7 is a diagram of the starting system for the freepiston engine diaphragm compressor.

FIG. 8 is a sectional view of the vibration switch for determining that the engine is operating.

FIG. 9 is a block diagram of the preferred general circuitry for the free-piston-engine diaphragm compressor.

Referring to FIG. 1, the free-piston-engine diaphragm compressor 11, includes an engine section 13, and a compressor section that are closely connected. The free piston includes a power piston 17 connected to a compressor piston 19 by means or" a piston rod 21. The power piston 17 reciprocates in an engine cylinder 23 having an inner liner 25. The power piston 17, provided with piston rings 27, divides the cylinder 23 into a combustion chamber 29 and a bounce and pumping chamber 31. The engine cylinder 23 is provided with a plurality of fins 33-33 for dissipating the heat of tie combustion process. Oil, for lubrication of the power piston 17, is provided to a fitting 35 through a passage 37 connected to an oil ring 39 that surrounds the liner 25. The liner 25 is provided with a plurality of ports 41-41 for introducing the oil into the combustion chamber 29.

The cylinder head 43, which is preferably integrally cast with the en ine cylinder 23, is provided with a spark plug 45 and a tap-off valve 47. The tap-off valve 47 directs high pressure combustion products from the combustion chamber 29 to a storage tank 49 (FIG. 7) which is a part of the starting system for the free-piston engine 13.

The air and fuel are mixed together and enter the cornbustion chamber 29 through a plurality of intake ports 51-51. The exhaust ports 53-53 are preferably arranged with respect to the intake ports 51-51 to produce a loop scavenging or a Schnurle-type system, i.e., the intake ports 51-51 have a slanted entrance passage 55 that directs the air toward the wall of the combustion chamber 29 near the cylinder head 43 after which the air turns toward the exhaust ports 53-53 forcing most of the gas from the previous cycle from the combustion chamber 29. (The port arrangement shown in FIG. 1 is for convenience only and is not the actual preferred arrangement.) The exhaust ports 53-53 communicate with an exhaust passage 57 which preferably is connected to a tuned expansion chamber (not shown) and a standard two-cycle automotive engine muffier (not shown).

The free-piston-engine diaphragm compressor 11 is capable of operating with a variety of fuels. The embodiment shown in FIG. 1 is adapted for burning natural gas. A carburetor 59 is provided having an air intake opening 61. An annular fuel-air space 63 surrounds the bounce and pumping chamber 31 and communicates with bounce and pumping chamber 31 by means of ports 65-65 that are opened and closed by the trailing edge 67 of the piston 17. A passage 69 leads from the carburetor 59 to a reed valve plate 71 that has a plurality of reeds 73-73 that are activated by pressure differences to open and close a plurality of fuel-air ports 75-75.

When the power piston 17 is in the position shown in FIG. 1, the fuel-air space 63 communicates with the combustion chamber 29 through the intake ports 51-51, the intake ports 51-51 being opened when they are uncovered by the leading edge 77 of the power piston 17. As the piston 17 moves toward the cylinder head 43 on the compression stroke, the bounce and pumping chamber 31 becomes larger. (The bounce and pumping chamber 31 is defined by the end of the piston 17 at the trailing edge 67, the cylinder liner 25 and the seal section 79.)

When the trailing edge 67 of piston 17 moves to uncover ports 65-65, the chamber 31, which up to this point was acting as a more or less blind rebound chamber becomes a pumping chamber. At about the same time as ports 65-65 are opened, the leading edge 77 of piston 17 closes the intake ports 51-51. The continued enlarge- 1 meat of chamber 31 causes a reduction of pressure in chamber 31 causing the reed valves 73-73 to open and a stoichiometric mixture enters fuel-air space 63 and chamber 31. The mixture continues to enter until the piston 17 reaches top dead point position.

On the return or power stroke, the chamber 31 decreases in size, the valves 73-73 close, and the fuel-air mixture in the fuel-air space 63 is pressurized until the trailing edge 67 of piston 17 recloses port 65. At about the same time, the leading edge 77 opens ports 51-51 allowing the pressurized fuel-air mixture to flow into combustion chamber 29 scavenging the chamber 29 and supplying the fuel-air mixture for the next power stroke. After port 65 is closed, chamber 31 again becomes substantially a blind chamber and the gas compressed therein by the movement of piston 17 cushions the power stroke (along with the action of compressor 15) and supplies rebound energy to drive piston 17 back on the compression stroke.

A compressor cylinder section 81 is attached to the end of the engine cylinder 23 and is provided with a central bore 83 that flares into a bell-shaped section 85. The compressor piston 19 reciprocates in the central bore 53 and acts on a column of fluid 87 (preferably oil) that forms a coupling to transfer the motion of the piston 19 to the diaphragm 89. The central bore 83 is separated from the bounce and pumping chamber 31 by the seal section '79. The seal section 79 includes two interference shaft seals 91-91 that contact the piston rod 21 and substantially prevent leakage between chamber 31 and central bore 83. An annular space 93 is positioned between the seals 91-91 and is vented to the atmosphere through a passage 95 allowing any gases or oil that might leak by the seals 91-91 to escape. The seal section 79 fits against the end 97 of the cylinder lining 25 and against a shoulder 98 iormed at the end of the cylinder section 81. Appropriate seals, such as O-ring seals 99-99, are positioned between the various surfaces of the cylinder liner 25, seal section 79, and cylinder section 81. A seal 1G1 is also provided between the engine cylinder 23 and the compressor cylinder section 81.

Reciprocation of the compressor piston 19 exerts a force on the fluid column 87. On the power stroke of the engine piston 17, the compressor piston 19 forces the fluid through a back-up plate 103 and against the diaphragm 89. FIG. 2 hows the preferred embodiment of the back-up plate 103 which is provided with a plurality of mounting holes 185-105, an O-ring type seal 107 and a plurality of substantially radial slots 109-1 09. The surface 111 mounted toward the diaphragm 89 is concave to provide for the flexations of the diaphragm 89. The diaphragm 89 ordinarily will not contact the back-up plate 103 at maximum compressor suction stroke (when the compressor piston 19 is at top dead center), but during engine shut-off, the compressor gas pressure forces the diaphragm 89 against the concave surface 111 of backup plate 103.

During the power stroke of the engine 13, when the piston 19 forces fiuid through the back-up plate slots 109-109, the diaphragm 89 is moved to force compressor gas through a plurality of discharge valves 113-113 mounted in a valve plate 115. The preferred embodiment of the valve plate 115 is shown in FIG. 3. The valve plate 115 is provided with a plurality of mounting holes 117-117 at its outer periphery and a concave surface that is mounted toward the diaphragm 89. An O-ring type seal 131 is positioned on the valve plate 115. The seal 121 is positioned to be opposite seal 107 on the back-up plate 103 so that the seals 107 and 121 cooperate to hold and seal around the periphery of the diaphragm 89. Adjacent to the seal 107, a groove 123 is provided on the back-up plate 103 and a groove 125 is provided adjacent seal 121 on the valve plate 115, which, together, form an annular space that permits the edge 127 of the diaphragm 89 to J flip up and down as the diaphragm 89 flexes to pump the refrigerant gas.

The compressor intake valve 129 is centrally positioned in the valve plate 115. Slightly more area is provided for compressor discharge (six discharge valves 113113 are included in the embodiment of valve plate shown in FIG. 3) than for intake since the power stroke of the engine 13 is somewhat faster than the rebound stroke. Two O-ring type seals 131 and 133 are positioned between the valve plate 115 and the compressor manifold 135. The seals 131 and 133 prevent leakage of the discharge gas to the intake gas-side and also leakage of the discharge gas from between the valve plate 115 and compressor manifold 135 to atmosphere.

The compressor manifold 135 is provided with a central inlet manifold 137 surrounded by an annular discharge manifold 139. An inlet line 141 connects the inlet manifold 137 to the evaporator (not shown) and a discharge line 143 connects the discharge manifold to the condcnsor (not shown).

Much of the expense in engines of this type is due to the alignment, tolerance and wear problems that are usually all closely related. The apparatus of this invention is constructed to avoid and eliminate some of these problems. Since the engine cylinder 23 and compressor cylinder section 81 are made separately and assembled, it follows that if these parts were prefectly aligned, the pistons 17 and 19 must be perfectly aligned. Although care is taken to establish and maintain good alignment, much of the problem is eliminated by a universal joint arrangement between the piston 17 and piston rod 21. The rod 21 fits into a space 145 in the piston 17. A washer 147 fits around the piston rod 21 and a nut 149 is threaded into the piston 17 holding the washer 147 in place. The piston 17 and rod 21 are alway in compression (by the combustion gases pushing the piston 17 toward the compressor or the compressor gases pushing the piston 19, via the diaphragm 89 and fluid column 87, toward the cylinder head 43) and the washer 147 is only under very light loads if it is ever loaded at all. However, the important feature of the connection shown is that the piston rod 21 is not firmly attached to the piston 17 so that alignment and tolerance discrepancies are allowable. Further, tolerance of misalignment conditions is allowed by the construction of the compressor piston 19. Since the fluid column 87 is used as a force transfer medium, sealing requirements are not as strict as they would be in other types of refrigerant compressors. When oil is used in the column 87, a leakage rate of about one gallon per hour can be tolerated. The oil merely passes by the piston 19 and out the passage 151 to an oil sump (not shown). A seal 153 is provided around the piston 19 to prevent excessive leakage. The piston 19 is also provided with a sleeve 155 selected from a material that is softer than the material of the piston 19. This feature centers the piston 19 in the bore 83. In addition, the soft material will catch any small foreign particles.

Since oil leakage around the piston 19 is permissible, the fluid lost from the fluid column 87 must be replaced on a regular basis. It was previously stated that the rebound for the engine piston 17 is provided in part by the chamber 31 and in part by the compressor gas exerting pressure on the diaphragm 89 and applying a force on the compressor piston 19 through the fluid column 87. The pressure in the bounce chamber 31 increases as the power stroke lengthesn slightly due to a decrease of fluid in the column 87 or greater displacement of the diaphragm 89 due to a decrease in compressor load. The increased pressure in the bounce chamber 31 is used to activate the oil pump 157 which is insensitive to normal-length strokes but is activated when the pressure in the bounce chamber 31 increases due to less fluid in the column 87 and the resulting longer piston strokes. A port 159 is provided in the seal section 79 that communicates with the pump 157 through a passage 161.

The pump 157 is shown in detail in FIG. 4. (Since the preferred fluid for column 87 is oil, the discussion of the related construction will be conducted with reference to an oil pump 157 and oil column 87.) A cylindrical body 163 has a threaded end 165 for engagement with a threaded socket 167 (FIG. 1) in the cylinder section 81. A threaded inlet 169 is provided with a fitting 171 that communicates with the oil sump (not shown). A threaded outlet 173 communicates through a check valve 174 (FIG. 1) and tube connection 175 (FIG. 1) with the oil column 87. The cylindrical body 163 is provided with a large diameter bore 177 that communicates with a small diameter bore 179. A piston 181 is slidably mounted in the large diameter bore 177 and is attached to a plunger 183 that is slidably fitted into the small diameter bore 17 9. An annular spring recess 185 at the end 187 of bore 177 and an annular spring recess 189 in piston 181 receive the ends of a spring 191 that urges piston 181 and plunger 183 toward the threaded end 165 of the cylindrical body 163. The large diameter bore 177 is provided, near end 187, with a plurality of grooves 193-193. When the piston 181 moves from a first position (the piston shown in FIG. 4) to a second position, whereby the front end 195 of piston 181 is opposite the grooves 193-193, high pressure gas on either side of piston 18.1 bypasses iston 181 through the grooves 193-193. The piston 181 is provided with a central, stepped recess 197 that communicates with a central bore 199 extending into the plunger 183. A lip 201 extends from the bottom 203 of recess 197 and surrounds bore 199. The wall of recess 197, near the bottom 203, is provided with a plurality of ribs 205 that serve as guides for a cap 207 that is positioned to engage the end of lip 201 and close off the bore 199. A spider 209 with a central spring guide and cap stop 211 is held in the recess 197 by a snap ring 213 and supports a spring 215 that urges the cap 207 against the lip 201. The bore 199 is provided with a port 217 that communicates with a variable volume chamber 219 (formed by bore 177 and the rear end 221 of piston 181) in the first position of piston 181 and that is closed in the second position of piston 181 (When port 217 is closed off by the plunger 183 moving deeper into bore 179).

The oil pump 157 operates when the oil column 87 needs oil. The reduction of oil in the oil column 87 decreases the resistance to the power stroke of piston 17, the power stroke lengthens slightly and the gas compressed in bounce chamber 31 takes on the increased rebound requirements by an increase in pressure. The spring 191 is selected to allow piston 181 to move only in response to the increased pressure in bounce chamber 31 acting through passage 161. As the piston 181 moves toward end end 187 of bore 177, gas trapped in chamber 219 escapes through port 217 and port cap 207 which acts as a check valve. Plunger 183 forces oil through outlet 173 and check valve 174. The gas forced from chamher 219 is replaced when piston 181 moves to the second position and end 195 moves opposite grooves 193-193 allowing the gas to bypass piston 181. The bypass (grooves 193-493), port 217, and cap 207 arrangement eliminate the necessity of porting chamber 219 to atmosphere and thus maintain a closed system preventing leakage from either the oil system or bounce chamber 31.

The timing for the ignition system is provided by positioning a pick-up device 223 to be triggered by the edge 225 of piston 19. FIG. 5 shows an enlargement of the pick-up 223 which includes a permanent magnet 227 surrounded by a coil 229. When the piston edge 225 passes the end of the permanent magnet 227 it breaks magnetic flux lines to produce a small electric current in coil 229 that triggers a high tension circuit 231 (shown in FIG. 6) that fires the spark plug 45. The cylinder section 81 has a socket 233 and an opening 235 for the end of the magnet 227 allowing the magnet 227 to be positioned very close to the piston 19. A seal 237 is provided around the pick-up casing 239, and the pick-up 223 is positioned and held in place by a spacer 241 and a hollow nut 243 7 that is threadedly engaged with the cylinder section 81. The leads 245 and 247 from coil 229 are connected to the high tension circuit 231 through a threaded electrical socket 249 (shown in FIG. 1).

The coil 229 has one lead 247 connected to ground and the other lead 245 is connected to a capacitor 251 and a transistor 253. With no pulse or current flow from coil 229, transistor 253 is off causing the power source 255 voltage to be presented to the base of transistor 259 via resistor 257 causing transistor 259 to conduct. By voltage divider action of resistors 263 and 265, due to conduction of transistor 259, transistor 267 receives the proper biasing voltage causing it to conduct. (Ionduction of transistor 267 causes the capacitor 277 to be charged. If there is a pulse of current from coil 229, the pulse turns on transistor 253 and turns otf transistor 259. Transistor 267 is also turned off since current flow through the resistor 263 and 265 is terminated. The diode 271 serves to back bias transistor 267 assuring the turnoff of transistor 267. Capacitor 27'7 discharges through the primary coil of the ignition coil 273 inducing a voltage in the secondary winding which creates a spark at the spark plug 45. The zener diode 279 prevents destruction of transistor 267 should the spark plug 45 be disconnected. The resistor 275 and capacitor 251 serve to hold the transistor 253 on for a short time after the turn-on signal is received from the coil 229.

The starting system for the free-piston engine diaphragm compressor 11 is shown in the diagram of FIG. 7. The tap-01f valve 47 bleeds off some of the high pressure combustion products in the combustion chamber 29 when the free-piston engine is operating. The combustion products are passed through duct 28 1, which includes a check valve 283 and a solenoid valve 285, to a storage tank 49 to provide a source of high pressure gas. From the storage tank 49 the high pressure combustion products are supplied through a duct 289 under the control of a solenoid valve 291 and a three-way valve 293. The passage to duct 289 through the solenoid valve 291 and the threeway valve 293 is closed while gas is being stored in the tank 49. The three-way valve 293 selectively connects duct 289 to passage 151 and also selectively connects passage 151 to a duct 295 that leads to the atmosphere. The combustion products from the combustion chamber 29 are stored at super atmospheric pressure (preferably about 350 p.s.i.g.) in storage tank 49 and in a quantity sufficient to make about fifteen starting attempts. When the engine 13 shuts down, solenoid valve 285 closes and solenoid 291 remains closed. When the engine 13 is to be restarted, solenoid valve 291 is opened and the three way valve 293 is positioned to connect duct 289 to passage 151. The compressor piston 19 is at top position, having been forced there by the pressure of the refrigerant acting against the compressor diaphragm 89 and oil column 87. The pressurized combustion products from the storage tank 49 are admitted to bore 83 above piston 19 and force piston 19 toward the diaphragm 89 in a rapid refrigerant compression stroke. Almost immediately the threeway valve is repositioned to connect passage 151 to duct 295 (and atmosphere). The refrigerant gas of the compressor and gas in bounce chamber 31 causes the pistons 17 and 19 to rebound on the compression stroke to start the engine 13. If the engine 13 does not start, the cycle is automatically repeated. The starting cycle is preferably arranged so that the piston 19 is forced down about two or three times before the ignition system is turned on in order to purge the engine 13 completely before any actual attempt at starting. It should also be recognized that a separate air compressor may be used to provide a pressure source for starting the engine 13. Since the engine 13 is preferably air cooled by a motor driven blower, this same motor can be used to drive the air compressor.

There are a number of ways to detect that the engine has started, such as a pressure transducer or vibration transducer. Thus, a pressure switch may be connected to sense the substantial pressure change that occurs in the carburetor manifold passage 69 when the engine is started. A vibrator switch 297 of the type shown in FIG. 8 and disclosed in US. Patent 3,132,221 may be used. The switch 297 is attached to the compressor 13, preferably at manifold plate which in turn is mounted on a spring 299. The vibration switch 297 includes a piston 301 mounted in a cylinder 303. A coil compression spring 305 has a lower convolution 307 engaged with the fiat top surface of the piston 301 and the upper convolution 309 engaged against a plate 311 formed with a central bleed port 313.

The casing cylinder 303 is counterbored at its respective lower and upper ends to provide an annular shoulder 315 at the lower end and an annular shoulder 317 at the upper end. For example, the lower end of the cylinder 303 is sealed closed by a disk 319 which seats on the shoulder 315. The disk 319 is formed of suitable insulating material and is formed with an air exhaust port 320'.

A rod 321 extends from the piston 301 and engages the lever 322 of a microswitch 323 (shown in FIG. 8 in the open position). I

The casing 303 at the upper counterbored end confines therein the spring engaging plate 311, which seats on the annular shoulder 317. The outer peripheral rim of the plate 311 and a diaphragm 325 are held against the shoulder 317 by a ring 324. The ring 324 slips into the top opening of cylinder 303 and substantially seals against manifold plate 135.

The diaphragm 325 or one way valve means 325 includes an upstanding bead 326 formed with ports 327 and is responsive to pressure from within the spring chamber 331 in cylinder 303 above the piston 301. The diaphragm flexes to open and close the central opening or port 313 in the spring plate 311. When the diaphragm 325 serves as a one-way valve means and is moved to open position by air compressed in the chamber 331, air then bleeds from the chamber 331 through opening 313 and diaphragm ports 327 to atmosphere through an exhaust port 328 through the ring 324 and wall of cylinder 303.

The bore of cylinder 303 is slightly larger than the circumference of piston 301 to provide a clearance therebetween, such as annular air gap 329 between it and the cylinder bore. A chamber 330, below the piston 301 exhausts through port 320 at low level vibration.

The contacts 371 of the microswitch 323 are connected to the main circuit for the engine as shown in FIG. 9. When the switch is at rest, the piston 301 is in a slightly lower (or extreme downward) position than shown in FIG. 8 and the contacts 371 are held closed. If the switch device is subjected to vibration along the longitudinal axis of cylinder 303, of suiiicient magnitude and frequency to overcome the force of compression spring 305, the piston 301 oscillates within the cylinder 303. During the resulting upward stroke of piston 301, air is drawn into lower chamber 330 through port 320. The air in upper chamber 331 is compressed until the pressure is sufficient to move diaphragm 32'5 away from port 313. Air then bleeds from upper chamber 331, through port 313, and diaphragm ports 327 to atmosphere through port 328.

Air continues to exhaust to atmosphere until the piston 301 reaches maximum height for a preset vibration level condition and the pressure in upper chamber 331 approaches atmospheric pressure. The diaphragm then returns and closes port 313.

On the downward stroke of piston 30]., air in the lower chamber 330 is exhausted through port 320 to atmosphere and air in upper chamber 331 drops below atmospheric pressure. The resulting differential pressure between upper and lower chambers 331 and 330 impedes further displacement of piston 301. Upward displacement of the piston 301 also moves the rod 321 upward and opens the microswitch contacts 371.

It can be seen that during continual vibration (or operation of the free-piston engine 13) responsive oscillations of the piston 301 within cylinder 303 maintain the rod 321 away from the microswitch lever 322 so that the contacts 3 71 remain open.

When the external vibrations cease, the force of compression spring 305 on piston 301 is opposed by the differential pressure existing between chambers 330 and 331. Air from chamber 330 slowly bleeds through clearance 329 into upper chamber 331. This action decreases the difierential pressure across piston 301, and the compression spring 305 returns piston 301 to the extreme lower position closing the microswitch 323.

FIG. 9 is a wiring diagram of a preferred circuit for the free-piston-engine diaphragm compressor 11. The system is supplied with ordinary 115 volt AC current. A transformer 351 reduces the 115 volt AC supply to 24 volt AC. The system is activated by an on-clf switch 353. Assuming that the area to be air conditioned requires cooling (or heating in case the diaphragm compressor is operated as a heat pump) the thermostat 335 will be closed activating the coil 357 of relay No. 1 which closes the contacts 359 of relay No. 1. Closing contacts 359 activates the spark plug power pack 361, the condenser fan 363, the evaporator blower 365, the engine lube motor 367, and the engine cooling blower 369. Assuming that the contacts 371 of the vibration switch 297 are closed, the cam motor 373 is also activated.

Ordinarily the air tank solenoid 291 is closed and the three-way valve 293 is positioned to connect passage 151 to duct 295. The cam motor 373 eventually closes cam switch 375 andactivates the coil 377 of relay No. 2 closing the contacts 379 of relay No. 2. This opens solenoid 291 and switches the three-way valve 293 connecting duct 289 to passage 151 to begin the starting cycle. Con tinned operation of the cam motor 373 opens cam switch 375 to reposition the three-way valve 293. The cycles continue until the engine vibrations causes the vibration switch contacts 371 to open and disconnect the starting apparatus from the circuit.

It has been indicated that it is preferable to cycle the engine two or three times before providing a spark to ignite the fuel-air mixture since this procedure purges the engine and provides a good fuelair mixture. The cam motor 373 is therefore arranged with appropriate cam surfaces to close a cam switch 380 only after cam switch 375 has been closed and opened two or three times dependent upon the number of purging cycles desired. Cam switch 380 is closed by the cam motor 373 during next closure of cam switch 375. The cam switch 380 is connected in series with the power supply generator 361. Closure of cam switch 380 causes the power supply generator 361 to be energized to supply a high voltage to spark plug 45 in response to the input signal produced by upward movement of the piston 19 past the pick-up device 223 initiated in response to the opening of cam switch 375. If this ignition cycle is successful, the vibration switch 297 opens contacts 371 causing the cam motor 373 to stop. The cam motor 373 is a type that does not coast when de-energized, consequently, cam switch 330 remains closed maintaining the circuit to the power supply spark generator 361 closed. If the ignition cycle is unsuccessful, the vibration switch 297 does not open contacts 371 and cam motor 373 continues to operate. The cam switch 380 opens upon further rotation of cam motor 373 and the purge cycles are repeated before the cam switch 380 is again closed for the next ignition cycle.

It will be understood, of course, that, while the forms of the invention herein shown and described constitute the preferred embodiments of the invention, it is not intended herein to illustrate all of the possible equivalent forms or ramifications of the invention. It will also be understood that the words used are words of description, rather than of limitation, and that various changes, such as changes in shape, relative size, and arrangement of parts may be substituted without departing from the spirit or scope of the invention herein disclosed.

What is claimed is:

1. In a free-piston-engine diaphragm compressor having a bounce chamber associated with said free-piston wherein there is a fluid column coupling between the free piston and the compressor diaphragm, the improvement of providing a fluid pump that is activated by increased pressure in said bounce chamber on overstroke of the free piston, said pump communicating with said fluid column to supply fluid thereto and thereby maintain fluid in said fluid column and control the stroke length of said free piston.

2. In a free-piston-engine diaphragm compressor refrigeration system including a combustion piston connected to a compressor piston with said compressor piston coupled to the compressor diaphragm by a fluid column at one end and having a variable-volume chamber at the opposite end with the volume of said variable-volume chamber being varied by reciprocation of said compressor piston, a starting system comprising:

(a) a body of high-pressure gas;

(b) communication means between said body of highpressure gas and said variable-volume chamber; and

(c) valve means positioned in said communication means, said valve means operative to release a selected amount of high-pressure gas into said variablevolume chamber whereby said compressor piston is moved rapidly in one direction by said high-pressure gas and rebounded in the opposite direction by compressor gas pressure acting against said fluid column to produce reciprocation of said combustion piston for starting said free-piston engine.

3. In a free-piston-engine diaphragm compressor refrigeration system including a combustion piston connected to a compressor piston with said compressor piston coupled to the compressor diaphragm by a fluid column at one end and having a variable-volume chamber at the opposite end with the volume of said variablevolume chamber being varied by reciprocation of said compressor piston, a starting system comprising:

(a) a body of high-pressure gas generated by operation of said refrigerant system;

(b) communication means between said body of highpressure gas and said variable-volume chamber; and

(c) valve means positioned in said communication means, said valve means operative to release a selected amount of higl1pressure gas into said variablevolume chamber whereby said compressor piston is moved rapidly in one direction by said high-pressure gas and rebounded in the opposite direction by compressor gas pressure acting against said fluid column to produce reciprocation of said combustion piston for starting said free-piston engine.

4. In a free-piston-engine diaphragm compressor including a combustion piston connected to a compressor piston with said compressor piston coupled to the compressor diaphragm by a fluid column at one end and having a variable-volume chamber at the opposite end with the volume of said variable-volume chamber being varied by reciprocation of said compressor piston, a starting system comprising:

(a) storage means communicating with the combustion chamber of the free-piston engine for collecting and storing a body of pressurized combustion gas produced during operation of said free-piston engine;

(b) communication means between said storage means and said variable-volume chamber; and

(c) valve means positioned in said communication means, said valve means operative to release a selected amount of pressurized combustion gas into said variable-volume chamber whereby said compressor piston is moved rapidly in one direction by said pressurized combustion gas and rebounded in the opposite direction by compressor gas pressure to produce reciprocation of the combustion piston for starting the free-piston engine.

5. In a free-piston-engine diaphragm compressor including a combustion piston connected to a compressor piston With said compressor piston Coupled to the compressor diaphragm by a fluid column at one end and having a variable-volume chamber at the opposite end with the volume of said variable-volume chamber being varied by reciprocation of said compressor piston, a starting system according to claim 4 wherein control means are connected to said valve means and the ignition system of said free-piston engine to activate said valve means at least once while deactivating said ignition system allowing said free-piston engine to be purged, and subsequently activating said ignition system and simultaneously activating said valve means to start said free-piston engine.

6. In a free-piston-engine diaphragm compressor including a combustion piston connected to a compressor piston with said compressor piston coupled to the compressor diaphragm by a fluid column at one end and having a variable-volume chamber at the opposite end with the volume of said variable-volume chamber being varied by reciprocation of said compressor piston, a starting system comprising:

(a) storage means communicating with the combustion chamber of the free-piston engine for collecting and storing a body of pressurized combustion gas produced during operation of said free-piston engine;

(b) communication means between said storage means and said variable-volume chamber;

(c) valve means positioned in said communication means, said valve means operative to release a selected amount of pressurized combustion gas into said variable-volume chamber whereby said compressor piston is moved rapidly in one direction by said pressurized combustion gas and rebounded in the opposite direction by compressor gas to produce reciprocation for starting the free-piston engine; and

(d) detection and control means connected to said valve means for detecting engine starting and for deactivating said valve means after said engine has started.

7. In a free-piston-engine diaphragm compressor including a combustion piston connected to a compressor piston with said compressor piston coupled to the compressor diaphragm by a fluid column at one end having a variable-volume chamber at the opposite end with the volume of said variable-volume chamber being varied by reciprocation of said compressor piston, a starting system according to claim 6 wherein said detection and control means is a vibration sensitive switch that is sensitive to vibrations of the operating free-piston engine.

8. In a free-piston-engine diaphragm compressor including a combustion piston connected to a compressor piston with said compressor piston coupled to the compressor diaphragm by a fluid column at one end having a variable-volume chamber at the opposite end with the volume of said variable-volume chamber being varied by reciprocation of said compressor piston, a starting system according to claim 6 wherein said free-piston engine includes a carburetor manifold passage and said detection and control means is a pressure switch connected to respond to the pressure change that occurs in said carburetor manifold passage when said free-piston engine begins operation.

9. A stroke control apparatus for a free-piston engine,

comprising:

(a) a cylinder substantially sealed at each end;

(b) a free-piston reciprocal in said cylinder, said free piston dividing said cylinder into a combustion chamher and a. bounce chamber, said bounce chamber providing at least a portion of rebound energy for said free piston subsequent to the power stroke;

(0) ignition, fuel-air supply and exhaust means in connection with said combustion chamber providing combustion means for driving said free piston on the power stroke;

(d) a working piston connected to said combustion piston;

(e) a fluid column coupling said working piston to a work load, said fluid column volume providing a limit for the stroke length of said free piston;

(f) a fluid pump connected to said fluid column and a source of fluid, said fluid pump communicating with said bounce chamber and activated to add fluid to said fluid column by excessive pressure in said bounce chamber produced by overstroke of said free piston wherein the volume of said fluid column is increased thereby decreasing the stroke length of said free piston.

10. A free-piston-engine diaphragm compressor comprising, in combination:

(a) a first cylinder;

(b) a combustion piston reciprocally mounted in said first cylinder, said combustion piston dividing said first cylinder into a combustion chamber and a bounce chamber;

(0) ignition, fuel supply and exhaust means connected to said combustion piston to provide combustion energy to reciprocate said combustion piston;

(d) a second cylinder substantially aligned with said first cylinder;

(e) a compressor piston attached to said combustion piston and reciprocal in said second cylinder;

(f) a flexible diaphragm closing ofl? one end of said second cylinder;

(g) a fluid column coupling said flexible diaphragm to said compressor piston whereby movement of said compressor piston against said fluid column flexes said diaphragm;

(h) a compressor chamber attached to said second cylinder, one wall of said chamber being said diaphragm;

(i) at least one inlet check valve in said compressor chamber and at least one outlet check valve in said compressor chamber whereby combustion of gases in said combustion chamber, provides energy to said combustion piston and said attached compressor piston moving said diaphragm via said oil column to compress gas in said compressor chamber forcing compressed gas through said at least one outlet check valve and the compressed gas in said compressor chamber and bounce chamber provide rebound energy to rebound said compressor piston.

References Cited UNITED STATES PATENTS 862,867 8/1907 Eggleston 230 1,563,166 11/1925 Corblin 230-49 3,065,703 11/1962 Harman 103-44 ROBERT M. WALKER, Primary Examiner.

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