US3769950A

US3769950A - Free piston engine starting apparatus

Info

Publication number: US3769950A
Application number: US00202973A
Authority: US
Inventors: A Braun
Original assignee: Individual
Current assignee: Tectonics Companies Inc
Priority date: 1971-11-29
Filing date: 1971-11-29
Publication date: 1973-11-06
Anticipated expiration: 1990-11-06

Abstract

Apparatus and method features are disclosed for starting free piston engines, and particularly for initiating combustion on the first power stroke of such an engine or on a recycled starting stroke. Such an initial power stroke is achieved by spark ignition of a suitable mixture in a combustion chamber of the free piston engine, preferably in the power cylinder. The first combustion is obtained at a pressure relatively lower than the compression ratio used for combustion during normal operation. Thus one may even use a negligible compression within such chamber to provide a first power stroke which initiates movement of the engine, but which provides substantially less dirving force than that which is provided by a regular power stroke once such an engine is running.

Description

United States Patent [191 Braun Nov. 6, 1973 FREE PISTON ENGINE STARTING APPARATUS Related [1.8. Application Data [63] Continuation of Ser. No. 66,386, Aug. 24, 1970,

abandoned.

[52] U.S. Cl. 123/46 A, 123/46 R, 123/46 SC, '123/179 BG, 123/179 R, 60/14, 60/DIG. l [51] Int. Cl. F021) 71/02 1 [58] Field of Search 123/46 A, 46 R, 46 B, 123/46 SC, 179 R, 179 B6; 60/14, 14 B, 17,

' DIG. l

[56] I References Cited 7 UNITED STATES PATENTS 929,696 8/1909 Oberly 123/46 R 1,732,694 10/1929 Pescara 123/46 R 2,423,720 7/1947 Mullesans et al. 123/46 R 2,434,877 H1948 Welsh et al. 123/46 R 2,462,745 2/1949 Horgen 123/46 R 2,983,098 5/1961 Bush .3. l23/46R 2,918,788 12/1959 Wachsmuth 60/14 13 3,071,120 l/l963 McCrory et al 123/46 R 2,982,271 5/1961 Heintz 123/46 A Primary ExaminerWendell E. Burns Attorney-Frederick E. Lange et a1.

[57] ABSTRACT Apparatus and method features are disclosed for starting free piston engines, and particularly for initiating combustion on the first power stroke of such an engine or on a recycled starting stroke. Such an initial power stroke is achieved by spark ignition of a suitable mixture in a combustion chamber of the free piston engine, preferably in the power cylinder. The first combustion is obtained at a pressure relatively lower than the compression ratio used for combustion during normal operation. Thus one may even use a negligible compression within such chamber to provide a first power stroke which initiates movement of the engine, but which provides substantially less dirving force than that which is provided by a regular power stroke once such an en glue is running.

17 Claims, 3 Drawing Figures PAIENTEnNnv s 1915 SHEET 10F 2 INVENTOR.

ATTOQAJESJ PMENIEUImv 5 I973 SHEET 2 OF 2 INVENTOR.

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FREE PISTON ENGINE STARTING APPARATUS This is a continuation of application Ser. No. 66,386, filed Aug. 24, 1970 now abandoned. I

The starting features are preferably combined with improved features for making a gradual transition from the initial or first combustion to a normal running condition. This transition is facilitated by controlling combustion during this transitional stage in response to a movement-related characteristic or parameter of the power piston, such as its velocity or rate of change of position in the power cylinder .of the engine. Thus, combustion is caused to occur at'a desired time which is related to the time the power system reverses direction at the start of a power stroke, without regard to variations from one stroke to another: in the actual physical position of the power piston along its path of movement in the cylinder at the moment of piston reversal. The original relatively low compression takes place at a position of the power piston where the various inlet and exhaust ports'are at least substantially closed, i.e., substantially before the normal inner reversal point of the power piston movement. By utilizing a movement-related power piston characteristic to control ignition on at least the transitional strokes subsequent to the first starting stroke, the chances of successful transition to a normal running condition are increased. Thus each subsequent combustion is timed close to the moment of reversal of the power piston, both during the gradually increasing transitional strokes. and then during the ultimate normal running power strokes of the engine. I

Features are also disclosed for moving the power piston for the starting combustion, for providing a suitable combustible mixture for the first power stroke, and for providing a combination of combustion-causing possibilities in which combustion may be initiated in timed relation to the moment of piston reversal for most operations, but in which position-responsive ignition means,

i.e., means actuated when the power piston reaches a particular physical position, may be used to initiate combustion at selected strokes, such as'a first starting stroke, or a later transitional or running stroke.

I BACKGROUND OF THE INVENTION 'latched, it has been known to utilize a separate source of air pressure to build up substantial pressure in a compressor or bouncer chamber against one face of a compressor or bouncer piston in such a direction as to urge the piston through its power section compression stroke. By releasing the latched piston assembly, this extra pressure quickly drives the piston through the compression stroke, hopefully .with enough force to achieve-either the high degree'ofcompression in the power cylinder combustion chamber which is necessary for compression ignition of a diesel engine or the somewhat lower but still very substantial'compression ratios customarily reached at the point of spark ignition for operation of a spark ignition engine. 1

'Some of these prior artfstarting devices, instead of latching the power piston assembly in one position and then releasing it suddenly, while under high pressure, have provided devices in which successive pulses of high pressure air in a bouncer or other chamber cause the free piston to cycle back and forth at gradually increasing stroke lengths and gradually increasing combustion chamber pressures, until finally the combustion chamber pressure is high enough to obtain a compression of spark ignition at an inner reversal or top dead point which corresponds very closely to the normal reversal point of the power piston during regular running conditions.

Those devices which include a latching arrangement for the power piston involve a sudden release of substantial force, all of which has a possibility of damage to the parts. Each of the prior art starting arrangements just discussed and others also require very substantial amounts of high pressure air in order to achieve the high level of compression in the combustion chamber which is required for normal ignition.

Moreover these prior art devices operate on a sort of all or nothing basis. Either the first ignition and power stroke is sufficient to get the engine close to normal running operation or another start must be tried. There is no satisfactory provision for gradual build up of successive power strokes through a transitional range in which a poor first stroke or a misfire prevents the achievement ofnormal running conditions.

SUMMARY OF THE PRESENT INVENTION The present invention provides apparatus and method features for achieving the initial power stroke in a single acting free piston engine under circumstances which do not require high compression in the combustion chamber and which do not require the use of large amounts of compressed air for the starting cycle. In its broadest aspect,-the invention includes the provision of a combustible mixture, suitable for spark ignition at a pressure which is either relatively close to the ambient or atmospheric pressure or at least substantiallybelowv the high compression ratio normally used during operation. This mixture is fed into the combustion chamber, the power piston is moved to a position in which at least the inlet ports of the power cylinder are substantially closed and the mixture is ignited bysa spark. The resulting combustion drives the power piston outwardly toward its outer dead point or reversal position, from which it will be returned for a subsequent compression stroke by the usual sources of return energy in such a single-acting free piston engine, i.e., the pressure developed in a bounce chamber, the pressure developed in the clearance volume of the compressor, or a combination of these or other similar forces.

While it is possible that such an initial low compression power stroke might generate sufficent return energy to bring the power piston back to a physical position within the power cylinder at which the positionresponsive timing means of prior art engines might be effective 'to cause further combustion and a relatively rapid transition to normal running conditions, the invention further provides for gradual transitional adjustment of the timing of the combustion-causing means. Such adjustment can be made manually. However, the preferred embodiment of the present invention combines thefurther feature of automatically controlling at least the subsequent transitional ignition or combustion points in a predeterminable time relationship to the moment at which the power piston reverses direction at the end of such a transitional compression stroke, without regard to variations in the actual physical position of the power piston within its cylinder at the moment of such reversal. Thus, if the force generated in the initial starting combustion stroke is only sufficient so that the power piston returns to a point substantially short of the normal desired inner reversal point for regular operations, the second combustion stroke will be initiated in response to a movement-related characteristic of the power piston which has a predeterminable time relationship to the moment of power piston reversal at the start of a power stroke This will provide a second power stroke. in a situation where the normal position-responsive ignition means of the prior art might not even be actuated. According to the present invention, the initiation of combustion close to the moment of power piston reversal at each successive transitional stroke, assures a gradually increasing build up from the initial starting power stroke, untilthe power piston finally reciprocates through a full normal running stroke.

A preferred embodiment of apparatus according to the present invention briefly includes sensing means which is responsive to a movement-related power piston characteristic or parameter which has a predeterminable relationship to the moment when the power piston reaches a reversal point at the end of each compression stroke and which is substantially independent of variations in the actual physical position of the power piston along its path within the cylinder at the moment of piston reversal for different power strokes. This sensing means provides a sensing signal analogous to the instantaneous values of the selected movementrelated power piston characteristic. The sensing signal is fed to a control means which in turn actuates the combustion-causing means at the desired moment in time related to the piston reversal. The control means may include adjustable timing or time-delay means to vary the desired time relationship between the actuation of the combustion-causing means andthe moment of piston reversal at the end of the compression stroke.

Although the preferred form of the invention includes the combination of method and apparatus features just described, it will be understoodthat the starting method and-apparatus have broad application and that the spark ignition of a charge of combustible gas at pressure substantially below normal compression or spark ignition pressure as a means of achieving the first starting movement of a single-acting free piston engine is capable of broader application with other methods and apparatus for controlling combustion during the transition from start-up to normal running conditions. This transition can even be made manually by suitable adjustment of the ignition point from the position at which the starting ignition occurs toward points successively closer to the desired top dead point or reversal point of the piston during normal running operation.

The present invention further provides a combination of reversal-related combustion causing means and position-responsive combustion causing means. Thus in one embodiment, the initial ignition for the first starting stroke may be responsive to the arrival of the power piston at a specific desired position, while combustion for subsequent transitional power strokes is caused by reversal-related ignition means. The reversal-related means in this embodiment is also preferably used to control combustion during normal operation.

In another embodiment, reversal-related ignition apparatus is so constructed that it can cause both the initial starting combustion, and the combustion for subsequent transitional power strokes. A separate positionresponsive combustion-causing means may also be provided in this embodiment to supplement the action of the reversal-related ignition apparatus.

With such a combination, ignition may be caused at a specific position during a particular power stroke either before or after the reversal-related apparatus would otherwise cause such ignition. Such a positionresponsive ignition can be used in a case where a single transitional or running compression stroke might otherwise tend to move the power piston inwardly beyond the desired optimum inner reversal point, or to provide a position ignition in case of unexpected failure of the reversal-related ignition on a particular stroke. If desired, the reversal-related ignition may be used only for the transitional and/or initial starting strokes, and a position-responsive ignition for subsequent normal engine operation. Thus the present invention also provides an advantageous combination of selectively operable reversal-related and position-responsive ignition apparatus in a free piston engine.

For the purposes of the present invention, a reversalrelated or movement-related power piston characteristic or parameter is defined broadly to be any characteristic which has a predeterminable relationship to the moment when the power piston reaches a reversal point at the end of a compression stroke, and which is substantially independent of variations in the actual physical position of the piston within its cylinder at the moment of piston reversal for different power strokes. Thus one such parameter sensing means gives a signal which is an indication of the movement or rate of change of position of the power piston within the free piston engine, as distinguished from the exact physical position of the piston along its path of movement.

For the purposes of the present invention, a movement-related parameter is to be contrasted with a position-responsive or displacement parameter, which directly indicates the position or displacement of the power piston. Examples of such displacement parameters are displacements or positions of parts mechanically linked to the moving power piston within a free piston engine and the displacement or position ofa cam follower riding on a cam surface fixed to the power piston within such an engine and designed to trigger at a substantially fixed position in each cycle. Thus the term position-responsive" is used herein in combination with such expressions as characteristic, parameter, ignition means, timing means", combustioncausing means or the like, for convenience in designating something which takes place at a predetermined location along the path of movement of a freely reciprocating engine element, without regard to variations in the time or the physical position at which that engine element reverses direction at the end of a compression stroke.

The term fuel" is used herein in a broad sense to include any gas or mixture of gases customarily used as a combustible charge in a free piston engine. For example, fuelmay be a combustible gas, a combustible mixture of gas and air, or a charge of air into which fuel is to be injected near the end of a compression stroke.

The terms combustion-causing means and ignition means andthe like, areused in a broad sense (except where the context requires aspecific interpretation) to include such devices as the spark plug and spark causing circuitry in a spark ignition engine and the fuel injection of a compression ignition engine, as well as other equivalents to such devices.

The term single-acting is used herein in connection with free piston engines in which a particular power piston and the parts connected therewith are driven by successive power strokes in only one direction, as distinguished from double-acting engines in which such parts are driven by successive alternating power strokes, with a power stroke in one direction followed bya power stroke in the opposite direction in successive cycles of operation.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings which form a part of this application,

FIG. 1 is a view, with certain parts shown schematically and in section, and with other parts shown in schematic diagram only, of one preferred embodiment of the invention;

FIG. 2 is an enlarged partial sectional view of a modification of one portion of. the device of FIG. 1, in which a position-responsive timingmeans for causing the first combustion on the initial starting stroke is automatically moved to an inoperative position for subsequent strokes, provided the engine starts and continues to run during transitional and/or normal operation; and

FIG. 3 is a view, similar to FIG. 1, of another preferred embodiment. 7

It will be understood that the drawings are designed to show the principles of operation according to the present invention and are in no sense to be understood as dimensional representations of the actual relative proportions involved of the parts. Moreover, reference in the following descriptions to left right, or other directions are to be understood as referring only for purposes of explanation to the relative directions as one views the accompanying drawings.

DESCRIPTION OFTHE PREFERRED EMBODIMENT 'In- FIG. I, a combination of elements according to one preferred form of thepresent invention is shown.

A free piston engine 17 has a power section 18 located at the extreme left of the engine and has a power piston 20 reciprocating along the longitudinal central axis of the engine within a power cylinder 21. The housing of engine 17 is generally designated at 22. The engine is provided with conventional means for introducing fuel and exhausting burnt fuel at.appropriate times in the engine cycle. For illustration, these are shown as respective inlet and

exhaust ports

14 and 16 in the wall of cylinder 21.

In this case, an outwardly-compressing compressor 23 is shown by way of example at the right end of engine 17. A shaft 24, extends horizontally along the longitudinal central axis of engine 17 and interconnects power piston 20 and a compressor piston 26. Compressor piston 26 is arranged to be reciprocally movable between the right face 36 of compressor piston 26 and the inner face of end wall 38.

A bouncer control valve 37 provides for the control of pressure in a chamber 42 formed between the left face 44 of piston 26 and inner wall 48. Valve 37 provides for the control of fluid pressure in chamber 42 and allows chamber 42 to operate as a negative bounce chamber, i.e., a chamber in which compression of fluid during a leftward'compression stroke of power piston provides additional energy for a power stroke to the right,'and in which the expansion of volume in chamber 42 during a power stroke to the right provides a realong the central longitudinal axis of engine 17 within duced pressure or partial vacuum in chamber 42 to facilitate the return stroke of

pistons

20 and 26 to the left.

A bouncer valve spring 40, which is adjustable as shown schematically at 46, can be set to establish a maximum pressure within bounce chamber 42. Higher pressures will then be vented through conduit 87, valve 37 and outlet 88.

The engine will also include other known features, the details of which are not essential to an understanding of the present invention. Thus, where shaft 24 penetrates

interior walls

48 and 49, conventional shaft seals (not shown) are provided to prevent the leakage of gas and lubricant around shaft 24 as it reciprocates.

To. facilitate an understanding of the starting features according tothe present invention, a description of additional portions of the complete free piston engine and its associated load device or compressor will be helpful. Thus, during operation, the output from compressor chamber 34 is fed through one-way valve 32 into a compressor discharge manifold 52. The discharge manifold has an outlet conduit 53 which communicates with a further conduit 54 connected to a suitable air storage tank or reservoir 56. Communication between

conduits

53 and 54 is controlled by a spring loaded discharge valve 57 which has a-loading spring 58 normally urging valve 57 to closed position. When the engine starts operation and sufficient pressure is generated within conduit 53 to overcome the resistance of spring 58, valve 57 can snap to a fully open position to provide complete communication from conduit 53 to conduit 54.-Thus, the output from the compressor will be fed to the storage reservoir-56 or to some other device for which'such output is designed.

In order to relieve the pressure within compressor chamber 34 whenever the engine shuts down, and thus facilitate the arrangements for starting the engine according to the present invention, a manifold pressure discharge conduit 59 is connected at one end to discharge manifold 52. The other end of conduit 59 is controlled by a valve 61 which is shown in FIG. 1 in its normal operating position in which conduit 59 is closed. Upward movement of the movable control portion of the valve against the urging of spring 62, effectively connects conduit 59 with a further conduit 63 by means of valve passage 64. Conduit 63 is connected to the chamber 65 providing a desired back-pressure on the rear side of valve 57. Thus when valve passage 64 is moved into upper operating position, the pressure within manifold 52, which is already applied to the upper or front side of valve member 57, will be applied through

conduits

59 and 63 to the rear side of valve 57. With equal pressure on each side of valve 57, the spring member 58 will immediately become effective to force the valve to closed position. The pressure within manifold 52,

conduits

59 and 63 and chamber 64 will then gradually be relieved, while valve passage 64 is in its upper position, through a suitable bleed orifice, shown schematically at 66, which communicates with conduit 63 between valve 61 and chamber 65.

Valve 61 is operated in any suitable manner at the time the engine is shut down, in order to insure closing of outlet valve 57 and thus prevent escape of pressure from receiving reservoir 56 back through the manifold 52. In effect, valve 57 and its associated controls provides a one-way check valve for the output from manifold 52. This check valve has a positive action in both directions between fully open position in which it accommodates the full output of compressor chamber 34, and a fully closed position which effectively retains the pressure in receiver 56.

Valve 61 may be connected to main ignition switch 67, for example, so that the valve is moved from the running position of FIG. 1 to its upper bleed position, with passage 64 connecting

conduits

59 and 63, whenever main switch 67 is opened to turn off the ignition. Switch 67 may be opened manually, or in response to predetermined pressure build-up in reservoir 56, or in some other suitable manner.

The present invention includes means to move the power and compressor pistons to a predetermined point in preparation for a desired starting cycle. For this purpose, a three-position valve 68 is provided which may be axially movable from one position to another and which is normally held in the position shown in FIG. 1 by equal and opposed spring means 69 and 70. In this normal running position, the central section 72 of valve 68 blocks communication between the conduits to be described below, which are used only for positioning the piston assembly prior to and during the starting operation. One incoming valve conduit 73 is connected by valves shown schematically at 74 and 76 to the pressure receiver or reservoir 56, or to a suitable source of auxiliary pressure, which need not have the high pressure which is ordinarily found in a storage reservoir such as 56. A reducing valve 77 may be used in conduit 73 to provide the desired reduced pressure.

Another conduit 78 on the same side of valve 68 as conduit 73 is connected so that it is open to atmosphere for relief of desired pressures as described below.

Valve 68 includes additional valve sections 79 and 81 which provide cross connections between the respective conduits 73 and 78 at one side of the valve, and

conduits

82 and 83 at the other side of the valve 68. Conduit 82 is connected at 84 to the compressor chamber 34. Conduit 83 is connected at 86 to a conduit 87 connecting the bouncer chamber 42 with valve 37 and bouncer outlet 88.

In operation, when engine 17 is shut down and it is desired to position the pistons and 26 for a starting cycle, valve 68 is first operated to the right so that valve section 79 connects conduit 73 with bouncer conduit 83 and thus introduces air under pressure from reservoir 56 and regulator 77 into the conduit 87 and bouncer chamber 42. At the same time, the valve section 79 also connects conduit 82 to exhaust conduit 78. Thus the compressor chamber 34 is effectively connected by a completely open connection to the atmosphere to relieve any pressure in that chamber. The resulting difference of pressure between the relatively higher pressure in bouncer chamber 42 and the ambient or atmospheric pressure in compressor chamber 34 forces compressor piston 26 and associated parts to the right toward the outer end of compressor cylinder 28.

If valve 68 is now permitted to return at least momentarily to its normal position as shown in FIG. 1, the compressor piston and associated parts will remain in their right hand position for starting.

According to the present invention, the starting is achieved by providing a suitable combustion chamber, feeding a charge of combustible gas into it, and then igniting this combustible mixture by a spark. Although this can be done in any suitable combustion chamber, i.e., any of the cylinders of the engine or even an antechamber to such a cylinder, it is preferable to use the regular combustion chamber in the power cylinder 21. This cylinder has been provided with ignition means in the form of spark plug 89 and is constructed in any event with the necessary strength to withstand the pressures and temperatures of combustion during normal engine operation. stroke, and of the For a starting cycle according to one embodiment of this invention, the power cylinder 21 is accordingly charged with a combustible mixture which may be introduced through its inlet port 14. A carburetor or mixer 91 is shown in block diagram and is connected in normal fashion at 92 to a regular gas supply 93. Thus, during normal running of the engine, the carburetor and gas supply will deliver the desired gas to the power cylinder 21 at the proper times when inlet 14 is open on an outward movement of piston 20 at the end of a power stroke to the right.

In order to achieve the starting of the engine according to the present invention a special starting valve means 94 is provided. This valve has two

valve sections

96 and 97. When valve section 96 is in position as shown in FIG. 1 during normal running of the engine, nothing passes through valve 94. When the valve is operated to the left, however, it connects an auxiliary air supply shown schematically at 98 through a conduit 99 through a conduit 101 leading to the carburetor 91. The desired connection is made by valve passage 102 in valve section 97. Valve section 97 may also include another passage 103 for connection of an auxiliary gas supply 104 through

conduit

106 and 107 to carburetor 91. i

Thus, operation of starter valve 94 to the left is designed to introduce into the power cylinder 21 an appropriate combustible starting mixture of gas and air, as needed during the starting cycle. It might be noted at this point that the auxiliary air is necessary to provide a combustible mixture on the initial starting stroke in those cases where the free piston engine normally operates with air supplied to the power cylinder or to the mixture by a suitable scavenge system. Such a system is shown schematically in FIG. 1 with reference to the chamber 107 between power piston 20 and inner wall 49. An inlet valve 108 permits air to enter chamber 107 when the power piston 20 is moving to the left. Then, when the power piston 20 returns to the right, for example during a power stroke, outlet valve 109 connects the scavenge chamber 107 either directly with intake 14 or with mixer 91, depending on the type of engine arrangement involved. Thus, during normal operation of the engine, the movement of power piston 20 with respect to scavenge chamber 107 will provide a sufficient flow of air to properly charge the power cylinder.

Since, however, such a scavenge system provides no air output when piston is at rest prior to a start, the present invention, through starter valve 94 and auxiliary air supply 98, provides the necessary proportion of air to achieve a combustible mixture in the power cylinder for the starting operation.

Thus, a starting cycle for the embodiment of FIG. 1, requires operation of starter valve 94 from the position of FIG. 1 to its left position in which section 97 of valve 94 becomes operative to connect the auxiliary air and gas supplies. At the same time, valve 68 (which has previously been operated to its right-hand position) should now be operated to the left, so that valve section 81 will connect the low pressure air from conduit 73 through conduit 82 to the compressor chamber 34 and vent bouncer element chamber 42 to the atmosphere at 78. Thus, the higher pressure in chamber 34 starts movement of compressor piston 26, shaft 24 and'power piston 20 to the left in a manner corresponding to its movement during a regular compression stroke. The pressure in chamber 34 need not be particularly high, however, since it is supplied over the relatively large area of compressor piston 26 and'needs to provide only a little more force than necessary to overcome the frictional'resistance of the parts. Thus the unique starting arrangement contemplated by this invention can even utilize a manual air pump for air at 73 and 98. The pressure at 73 may be as low as only 2 p.s.i.g. (pounds per square inch gauge,i.e. above ambient pressure).

As the pistons move to the left, power piston 20 will first move past the outer end of inlet port14 and then gradually close this port, as well as exhaust port 16. As soon as the intake and

exhaust ports

14 and 16 are substantially closed, or shortly thereafter, the ignition system is operated to provide a spark at 89 to ignite the combustible mixture in power cylinder 21 and provide a first combustion or power stroke of piston 20 to the right. The spark for this initial combustion is provided in this embodiment by a position-responsive actuator, i.e., an arrangement in which ignition is triggered-at a specific position of the power piston 29 and associated parts along the path of movement of the piston. By way of example, a setof breaker points'112 is supported on an adjustable slide 113, which is moveable axially of the engine within a guide slot 114. A manual adjusting knob 116 extends outwardly of the casing to permit adjustmentof the position at which the contacts will be actuated.

As is customary in the art, one of the breaker points 112 is carried on a movable supporting arm 117, and the other is on a relatively stationary arm 118. An intermediate spring 119 normally urges the points apart from each other, and a stop 121 limits the upward movement of the movable contact arm 117. This movable arm carries an actuating portion 120 designed for engagement by a timing cam 122, suitably mounted on a support 123 carried by thepiston shaft 24, or by some other suitable portion of the engine which moves in synchronism with the power piston 20. The movable contact is connected in known manner by a suitable wire 124 to a junction point 126 in circuit with the positive side of the battery 127, the negative side of which is grounded at 128. Another wire 129 connects the fixed contact through starting switch 136, junction 141, and main switch 67, with the primary winding 131 of ignition coil 132. The secondary winding 133 of ignition coil 132 is connected at 134 to the spark plug 89,

and the respective ignition coil windings 131 and 133 are grounded, as shown, to complete the normal circuit.

In the embodiment of FIG. 1, the starting switch 136 is operated when it is desired to have the breaker points 1 12 in circuit during that portion of the starting or running of the engine when ignition is to be timed at a particular position of the power piston 20 along its path of movement in the power cylinder. In FIG. 1, the power piston 20 is shown at the outer dead point or reversal point of its path with the power face of the piston at the location indicated by the arrow and dotted line 137. During normal operation itis desirable that the piston move to the left during a compression stroke, until it reaches a normal inner reversal point indicated by the dotted arrow 138.

According to the present invention, as power piston 20 moves from position 137 toward position 138 and the power cylinder 21 is filled with a suitable combustible mixture through operation of valve 94, the timing position adjustment at 116 is set initially, so that the breaker points will be actuated by cam 122 as the inner power piston face reaches the intermediate point 139 along its path, i.e., some time after the intake and exhaust valve ports have been substantially closed, but without necessarily waiting until the piston completely reaches its inner reversal point 138. At this point 139, the combustible mixture in 21 will be under substantially less pressure thanthe compression ratios which would be customary in regular running of the engine with a full compression stroke. The starting movement of piston 20 from right to left, as already described, is under only the pressure fed by valve 68 to chamber 34. Since the area of piston 26 is generally greater than that of power piston 20, a given pressure in chamber 34 can produce a somewhat higher pressure in the power cylinder, but the present invention requires no particular pressure therein.

In any event, the ignition contacts are set by adjusting member 116 to produce the initial combustion for a first power stroke of the power piston 20 at a point which will surely be reached as the piston moves from right to left, without necessarily waiting for the piston to movefarther to the left than the intermediate point 139. This initial low compression power stroke will ordinarily provide less force than a normal later power stroke after the engine has been started, but it will be sufficient to start the reciprocation of the pistons. Ignition adjustment member 116 may then gradually be moved to the left, so that successive power strokes are started by combustion at points gradually closer to the normal desired inner reversal point 138. After the initial combustion stroke, the movement of power piston 20 will also start operation of the normal scavenge air system through chamber 107 and valve 109, so that subsequent combustion can be achieved in more normal manner by the regular supply of gas through mixer 91 and air from the scavenge system. Thus'valve 94 can be operated back to its right-hand position to cut off the auxiliary gas and air supplies, which are provided primarily to insure a suitably proportioned combustible mixture for the initial starting stroke.

In the operation just described, the gradual adjustment of the point of ignition from the starting stroke combustion at piston position 139 toward the normal running condition at which combustion occurs closer to the normal inner reversal point 138 is achieved by adjustment of the physical location along the path of piston movement at which the spark ignition is provided. According to a further feature of the invention, however, there are special advantages in controlling the initiation of combustion, at least during the transition from the first starting stroke to a normal running condition, and preferably also during the normal running condition by timing the point of ignition at a predetermined moment in time related to the moment when the power piston actually reverses direction at the end of a compression stroke and the start of an immediately following power stroke. Such reversalrelated timing is independent of variations which may occur in a free piston engine between the actual physical position of the power piston 20 at the moment of reversal for different successive power strokes.

For this purpose another set of breaker points 137 is shown in FIG. 1 connected in parallel to the breaker points 112. Moveable breaker point arm 138 has its contact point connected to the junction 126 with the positive side of battery 127. Fixed breaker point 139 is connected to junction point 141 in wire 129 leading to the primary winding 131 of coil 132. Junction 141 is between the main ignition switch 67 and the starting switch 136, so that breaker points 137 will be in circuit with primary winding 131 at all times, whether starting switch 136 is open or closed. Thus starting switch 136 may be closed for the starting operation, so that contacts 112 provide the initial position-responsive ignition at sparkplug 89, when piston 20 reaches the preselected starting point 139. Switch 136 may then be opened, so that the ignition point for subsequent transitional and running power strokes is controlled by breaker points 137. l The making and breaking of these points is controlled by an actuating member 142 of a control means 143, which is designed to make and break the points 137 at a preselected time relationship to the moment of reversal of power piston 20 at the end of a compression stroke. The control means shown in FIG. 1 includes a cylinder 144 providing a control pressure chamber 146 in which a piston 147 connected to output member 142 may reciprocate. Piston 147 is urged to the left by a spring 148, the tension of which is adjustable by a control knob 149, threaded into the endof the cylinder. Thus, when the pressure in chamber 146 increases to a preselected point, determined by the adjusted force of reference spring 148, the output member 142 will be urged to the right to cause engagement of the contacts 137. A decrease in the control pressure 146, at an adjustable time which is related to the inner reversal point of the piston, then breaks the contacts 137 for producing a spark at 89.

Pressure chamber 146 is designed to receive a pressure sensing signal which is proportional to a movement-related characteristic or parameter of power piston 20. In this case, pressure'chamber 146 receives pressure signals through a conduit 151 connected to a pressure sensing cylinder 152. A pressure sensing piston 153 moves in cylinder 152 and is connected at 154 to a member 156 carried by the shaft 24. Thus the movement of sensing piston 153 corresponds to the movement of the power piston 20 and generates pressures in cylinder 152 and transmits them to control chamber 146 in predetermined relationship to the velocity and/or acceleration of the power piston 20 along its path. Control means 143 may include adjustable timing means which in this embodiment is illustrated by i a controlled orifice 157, which is adjustable as shown schematically at 158. Orifice 157 provides a desired rate of relief of pressure from control chamber 146 and accordingly times the moment at which breaker points 137 separate.

Thus, as power piston 20 moves to the left during a compression stroke from its outer dead point 137 toward its inner reversal point 138, piston 20 will first accelerate to a maximum velocity at some intermediate point along the path and the velocity will then gradually decrease. The velocity reaches zero at some point along the path where the forces tending to move piston 20 to the left are balanced and then exceeded by the forces tending to move it to the right. During the initial acceleration to the left, sensing piston 153 provides a pressure signal which causes an increase in pressure in control chamber 146 faster than the orifice 157 can relieve such pressure. Contacts 137 will then close. As the piston 20 slows down on its leftward stroke just prior to reversal, however, the rate of input of the pressure signal from piston 153 decreases. The orifice 157 can then relieve the pressure in chamber 146 to cause breaking of the contacts at 137. Thus by appropriate adjustment of the spring tension at 148 and the orifice size at 157, breaker points 137 can be closed and opened to provide a spark at 89 in the desired predetermined time relationship at or about the time that the power piston 20 reverses direction. This timing will take place, whether the piston, at the time of reversal, is close to the normal operating inner reversal point 138 or whether it is close to the starting point 139 or somewhere else along its path within the operating range of the parts.

The breaker pointsl12 may be effectively disconnected and kept from causing premature ignition after the first starting combustion, by opening manual starting switch 136 so that the control system 143 and breaker points 137 can take over the subsequent ignition in relation to the inner reversal points of the power piston 20. Alternatively, since the adjustment of member 116 in slot 114 permits movement of the contacts to the left, the contact points 112 can be moved far enough to prevent engagement of the cam 122 with member 120, even when power piston 20 reaches its normal inner reversal point 138. This will effectively disable or inactivate the position-responsive ignition means 112.

Still another embodiment for effectively disabling the breaker points 112 after the first starting combustion is shown in FIG. 2. In this case, instead ofa fixed cam 122 on member 123 connected to piston shaft 24, the member 123A, FIG. 2, is provided with a movable timing cam portion 161 at the end of a mass 162, supported for sliding movement within a guide channel 163 in member 123A. A spring 164 normally urges mass 162 to the position shown in FIG. 2 in which cam portion 161 will project far enough to actuate the portion 129 of breaker points 112 in the same manner described for fixed cam 122 of FIG. 1. Thus, during the initial compression stroke, which is at relatively low velocity of movement from right to left, mass 162 will remain in the relative position shown, and the initial spark will be provided at the desired power piston position 139 of FIG. 1.

If ignition is successful, the power piston 20 will then be accelerated sharply to the right during the initial power stroke. The inertia of mass 162 will urge it against spring 164 to a relatively retracted position, in which cam portion 161 will not project far enough to engage the portion 120 on subsequent strokes. To keep the cam portion 161 in its retracted position as long as the piston assembly is being accelerated rapidly in successive power strokes, the mass 162 is connected by shaft 166 to a plunger 167 in an auxiliary cylinder or chamber 168. Plunger 167 and cylinder 168 provide a dash-pot or damper effect. A large opening 169 at the right end of cylinder 168 permits the entrance of air and facilitates movement of plunger 167 to the left, when the acceleration of the power stroke causes relative movement of mass 162 and associated parts in that direction. This movement is further permitted by the one-way valve 171 at the left end of dash-pot cylinder 168, which permits rapid escape of air at the left of plunger 167. Check valve 171, does not, however, permit the entrance of such air, which can only be restored through a small bleed orifice 172. The size of this orifice is so chosen that the rate of return movement of plunger 167, shaft 166 and mass 162 from left to right under the urging of spring 164 will be too slow to project cam portion 161 between successive power strokes in which combustion is successfully achieved. If, however, the engine is stopped, either intentionally or otherwise, then the continued entrance of air through orifree 172 permits spring 164 to restore the parts to the position shown in FIG. 2, so that cam portion 161 will be ready to actuate breaker points 112 for another starting stroke in a new starting cycle. A further embodiment of the invention is shown in H6. 3 in which a preferred form of reversal-related control apparatus for spark ignition is operatively connected in a manner designed to control ignition both on an initial starting stroke and during the transition from the first starting stroke to a normal running condition, as well as during the transition from the first starting stroke to a normal running condition, as well as during the ultimate normal running operation of the engine.

In this case, a modified starting mixture control valve 94A is used. Instead of controlling the flow of both auxiliary gas and air to the mixer and power cylinder for the starting stroke and then stopping such flow when the regular gas supply and scavenge air systems handle the. subsequent power strokes, the valve 94A'changes only the auxiliary air supply and connects the regular gas supply to the mixing valve 91 in both positions of valve 94A. Auxiliary air is provided byvalve section 97 during starting, until the usual scavenge air system provides enough air. The auxiliary air is then discontinued by section 96A of valve 94A. Both

valve sections

96A and 97 keep the gas supply connected to the mixer, not only for the starting power stroke, but also during transition and normal running of the engine.

This preferred control mechanism 174 utilizes the principle of balancing dynamic pressures above and below a moveable diaphram to control the ignition breaker points 137. For this purpose the control unit is connected to receive the pressure signals from conduit 151, as generated by sensing piston 153 in response to velocity and acceleration of the power piston 20. Conduit 151 feeds its pressure signals to

branches

176 and 177 which are connected to respective lower and

upper pressure chambers

178 and 179 located below and above a flexible diaphram 181 suitably supported in a housing 182. A controlled exhaust orifice 183, the effective opening of which may be adjusted as shown schematically at 184, is connected to the lower chamber 178. Another open exhaust conduit at 186 is connected to the upper chamber 179.

The center portion of flexible diaphram 181 is secured to an operating shaft 187 which extends vertically upward to serve as an output member for actuating the breaker points 137. A collar 188 secured to shaft 187 engages a stop 189 to limit the downward movement of the shaft 187 and establish a rest position for diaphragm 181. The parts are held downwardly in this position by a relatively light spring 191, the tension of which may be adjusted by a threaded knob or collar member 192. The upper end 193 of shaft 187 has a telescoping resilient override connected at 194 with the contact actuating member 196. Member 196 causes engagement of breaker points 138 and 139 when the shaft 187 and diaphram 181 are moved upwardly and then opens the contacts when the diaphram and shaft move back down.

In operation, when power piston is moved slowly to the left in the manner described in connection with FIG. 1 in order to achieve initial combustion, the increasing pressure signal fed through conduit 151 will be distributed both above and below diaphragm 181. The more restricted orifice 183 below diaphragm 181, however, causes a relative pressure differential, so that the pressure below the diaphragm exceeds that above the diaphragm. Thus shaft 187 is moved upwardly to cause engagement of the breaker points. As power piston 20 moves farther to the left and reaches approximately the desired point of initial ignition, even the slight compression within the power cylinder 21 will slow the movement of power piston to the left. As this movement slows down, the relief of pressure from the orifice 183 exceeds the decreased input at 176 and soon equalizes the pressure below and above diaphragm 181. Shaft 187 is then urged downwardly by spring 191 to open the breaker points at 137 and cause the initial spark.

In this embodiment, for the operation just described, it will be understood that the contact points 112 will be either omitted entirely, or moved far enough to the left so that they will not be actuated, i.e., so that cam 122 will not reach actuating portion 120.

The same type of action just described for the first starting stroke will occur during the transitional firing strokes, as the piston movement gradually builds up to its desired normal strength length, except that the action will be more rapid. in this more rapid action, in case the bleed action of restricted orifice 183 is not sufficient to lower the pressure in chamber 178 before the power piston reaches its reversal point, the diaphragm will at least be moved suddenly downwardly to open the breaker points no later than a point immediately after the reversal of the inner dead point. At this point, with sensing piston 153 beginning to move to the right, the pressure in conduit 151 and in

branches

176 and 177 will be rapidly reduced. This reduction will be more effective, however, in lower chamber 178, since the rate of pressure removal through conduit 176 cannot be equalled by the return movement of air in through the restricted orifice at 183 as rapidly as the pressures within the upper chamber 179 may be restored through the greater opening of conduit 186. Thus there will be a sudden positive downward movement of the diaphragm 181 and shaft 187, until

stops

188 and 189 engage each other. Thus, depending on the actual adjustment at 184 of orifice 183, the spark can be caused to occurjust prior to, at, or no later than immediately after the reversal of the power piston at its inner reversal point, i.e., the end of a compression stroke and the start of a new power stroke. Thus the entire operation of starting the engine, passing through a transitional stage of gradually lengthening power strokes, and then running at normal operation'with piston reversals at or near the normal desired inner dead point, can all be achieved with the control unit 174.

Although breaker points 112 could be omitted entirely, as previously mentioned, they have been retained in the embodiment of FIG. 3, so that the device of FIG. 3 can again use a combination of positionresponsive ignition means, and reversal-related ignition means. For example, by setting contacts 112 at its extreme left position in FIG. 3, cam 122 will always actuate these breaker points at, or even slightly beyond, the desired inner reversal point of piston 20. Thus the breaker points 112 can be set to correct what might otherwise be too long a compression stroke to the left resulting from some abnormality in operation of the engine. Points 112 then provide ignition no later than the point at which cam 122 engages operator 120, in case the piston might not otherwise reverse direction, until it had penetrated slightly farther into the head of the power cylinder.

Thus, as described above, the present invention is capable of utilization in several forms, in each of which the timing of combustion in predetermined time relationship to the moment of reversal of the power piston at the end of the compression stroke provides advantageous operation during at least the transitional period between the first starting stroke and the achievement of normal running conditions. In the device of FIG. 1, this reversal-related control of ignition is combined with a position-responsive ignition control, and the latter is used to control the initial spark for the first power stroke during the starting cycle. In the embodiment of FIG. 3, the position-responsive set of breaker points 112 may either be omitted or disconnected completely on the one hand, or may be utilized in combination with the reversal-related ignition control 174 to correct special situations in which the reversal-related system might provide a spark somewhat later than desired or might unexpectedly fail to provide a spark at all.

The principles of the invention can be carried out with a wide variety of psecific embodiments which may differ from those shown in FIGS. 1 to 3 in ways which will be readily apparent to those skilled in the art. For example, other types of reversal-related control units responsive to a power piston movement-related characteristic may be utilized in addition to systems based on the sensing of pressure. Other fluid control systems, as well as electrical or mechanical equivalents thereto can be used to achieve the desired starting cycle, the preferred control of the transition from initial starting combustion to a running condition, and the ultimate timing of ignition during normal operation of such a free piston engine.

The foregoing specification has accordingly set forth the nature and principles of the present invention together with illustrative variations in the preferred embodiments by which the invention may be practiced.

Now, therefore, what is claimed is:

1. In a free piston engine having a power cylinder with inlet and exhaust ports operable between closed and open positions in desired normal operating sequence, a power piston reciprocally movable in the power cylinder along a path between desired normal inner and outer piston reversal points which may vary from stroke to stroke, means for causing repetitive combustion in said power cylinder to drive said power piston during normal engine operation, at least one other cylinder, a second piston movable therein, and means interconnecting said power and second pistons for simultaneous reciprocal movement in their respective cylinders, the improved starting means comprising, in combination, piston-moving means for moving the power piston inwardly toward its desired normal inner reversal point from an outer preliminary starting position to an intermediate first relative position of the pistons at which the pressure in the power cylinder is substantially below the compression pressure customary in the power cylinderjust prior to combustion during normal engine operation, means defining a starting combustion chamber in connection with one of said cylinders, means for supplying a combustible starting mixture to said starting combustion chamber before the pistons reach said intermediate position, spark means for igniting said starting mixture within the starting combustion chamber, and means for initially energizing said spark means as said piston-moving means moves said pistons to said intermediate first relative position and thereby causing combustion of the combustible starting mixture, the energy released by said starting mixture combustion being transmitted to one of said pistons to start rapid reciprocal movement of the power piston toward its outer desired reversal point and thereby initiate normal engine operation, and said means for causing repetitive combustion in said power cylinder during normal engine operation being thereafter operable to cause such combustion at other relative intermediate positions of the power piston at which a combustible mixture is under gradually higher and more normal compression pressures within the power cylinder during transitional operation while the engine is assuming normal operating condition and at the desired normal inner reversal point during such normal engine operation.

2. A free piston engine according to claim 1 in which said starting combustion chamber is within the power cylinder and includes the portion of the power cylinder which serves as a power chamber for repetitive combustion to drive said power piston during normal engine operation.

3. A free piston engine according to claim 2 in which said means for causing repetitive combustion during normal engine operation includes said spark means, and reversal-related control means for energizing said spark means during the compression strokes of the power piston during transitional and normal operation and independently of any specific position of the power piston along its path of movement within the power cylinder.

4. In a free piston engine having a power cylinder with fuel inlet means and exhaust means operable between closed and open positions in desired normal operating sequence, a power piston reciprocally movable in the power cylinder along a path between desired normal inner and outer piston reversal points which may vary from stroke to stroke, means for causing repetitive combustion in said power cylinder to drive said power piston during normal engine operation, at least one other cylinder, a second piston movable therein, and means interconnecting said power and second pistons for simultaneous reciprocal movement in their respective cylinders, the improved starting means comprising, in combination, means defining a starting combustion chamber in connection with one of said cylinders, means for supplying a combustible starting mixture to said starting combustion chamber, spark means for igniting said starting mixture within the chamber, and means for initially energizing said spark means at a first relative position of the pistons at which the pressure of the mixture in said starting chamber is substantially below the compression ratio customary during normal running of such engines and thereby cuasing combustion expansion ofthe combustible mixture, the energy released by said cumbustion expansion being transmitted to one of said pistons to start rapid reciprocal movement of the power piston toward its outer desired reversal point and thereby initiate normal engine operation, and said means for causing repetitive combustion in said power cylinder being operable to cause such combustion at other relative positions of the pistons at which a combustible mixture is under substantially higher and more normal compression pressures within the power cylinder during transitional operation while the engine is assuming normal operating conditions and during normal engine operation, said starting combustion chamber beingwithin the power cylinder and including the portion of the power cylinder which serves as a power chamber for repetitive combustion to drive said power piston during normal engine operation, and said free piston engine having means for moving said pistons to a preliminary starting position within their respective cylinders prior to operation of the means for initially energizing said spark means, and means for moving said power piston toward its inner reversal point from said preliminary starting position to said first relative position at which the spark means is initially energized, said preliminary starting position being close to the outer desired reversal point of the power piston and said first relative position of the piston being an intermediate position in which the inlet and exhaust means are substantially closed and the combustion gases exert a substantial pressure against the power piston when ignited and drive the power piston in the direction of its desired power stroke.

5. A free piston engine according to claim 4 in which said starting means is responsive to air at pressure as low as only 2 p.s.i.g. (pounds per square inch gauge, above ambient pressure) to move the pistons from their preliminary starting position to said first relative position.

6. In a free piston engine having a power cylinder with fuel inlet means and exhaust means operable between closed and open positions in desired normal operating sequence, a power piston reciprocally movable in'the power cylinder along a path between desired normal inner and outer piston reversal points which may vary from stroke to stroke, means for causing repetitive combustion in said power cylinder to drive said power piston during normal engine operation, at least one other cylinder, a second piston movable therein, and means interconnecting said power and second pistons for simultaneous reciprocal movement in their respective cylinders, the improved starting means comprising,

in combination, means defining a starting combustion chamber in connection with one of said cylinders, means for supplying a combustible starting mixture to said starting combustion chamber, spark means for igniting said starting mixture within the chamber, and means for initially energizing said spark means at a first relative position of the pistons at which the pressure of the mixture in said starting chamber is substantially below the compression ratio customary during normal running of such engines and thereby causing combustion expansion of the combustible mixture, the energy released by said combustion expansion being transmitted to one of said pistons to start rapid reciprocal movement of the power piston toward its outer desired reversal point and thereby initiate normal engine operation, and said means for causing repetitive combustion in said power cylinder being operable to cause such combustion at other relative positions of the pistons at which a combustible mixture is under substantially higher and more normal compression pressures within the power cylinder during transitional operation while the engine is assuming normal operating conditions and during normal engine operation, said starting combustion chamber being within the power cylinder and including the portion of the power cylinder which serves as a power chamber for repetitive combustion to drive said power piston during normal engine operation, and said free piston engine having piston positioning means for moving the power piston inwardly toward its desired inner reversal point from a preliminary starting position located outwardly beyond said first relative position, and fuel delivery means having a member operable between a starting position in which the fuel delivery means feeds a combustible auxiliary starting mixture to the power cylinder and a running position in which the fuel delivery means feeds a normal operating mixture to the power cylinder, said fuel delivery means member being selectively operable to its starting position, before said piston positioning means moves the power piston inwardly to said first relative position.

7. A free piston engine according to claim 6 in which the piston positioning means includes valve means having a first port for connection to a source of air pressure, a second port connected to the other cylinder for selectively admitting air to one end of that cylinder and thereby moving the second piston and power piston toward the inner reversal point and toward said first relative position, and a valve member movable between at least a normal running position in which the valve member prevents the passage of air from the first port to the second port and a starting position in which the valve member connects the first and second ports.

8. In a free piston engine comprising a power cylinder having fuel inlet means and exhaust means, a power piston freely reciprocable in the cylinder along a path between desired normal inner and outer piston reversal points which may vary from stroke to stroke, and means for causing repetitive combustion in the power cylinder to drive the power piston outwardly toward its outer desired reversal point in successive power strokes, the improved starting and ignition means comprising means for feeding a combustible starting mixture to said fuel inlet means and power cylinder, means for moving the power piston inwardly toward its desired inner reversal point from a preliminary starting position spaced along its path outwardly of the inner reversal point, and means for initially igniting said starting mixture within the power cylinder when the moving means has moved the power piston inwardly from the preliminary starting position to a first relative position of the power piston at which the pressure of the starting mixture is substantially below the compression pressure customary during normal running of such engines.

9. A free piston engine according to claim 8 in which at least one of the means for causing repetitive combustion and the means for initially igniting said starting mixture is a reversal-related means.

10. A free piston engine according to claim 9 in which the means for causing repetitive combustion is a reversal-related combustion causing means.

11. A free piston engine according to claim 10 in which the means for initially igniting said starting mixture is a position-responsive ignition means.

12. A free piston engine according to claim 1 1 having disabling means for discontinuing effective operation of said position-responsive means after the initial actuation of the ignition means.

13. A free piston engine according to claim 12 in which said disabling means includes a cam-supporting housing operatively connected to move with the power piston, and an acceleration responsive cam supported in said housing for movement between a normal starting position in which the cam is effective to actuate the ignition means and a retracted position in which the cam is withdrawn from its effective starting position, and means automatically moving the cam to retracted position in response to acceleration of the piston during a combustion power stroke.

14. A free piston engine according to claim 8 in which each of the means for causing repetitive combustion and the means for initially igniting the starting mixture is a reversal-related means.

15. A free piston engine according to claim 8 having reversal-related means operatively connected to each of the means for causing repetitive combustion and the means for initially igniting the starting mixture, said engine also having position-responsive means operatively connected to the means for causing repetitive combustion and actuating the means for causing repetitive combustion at a predetermined power piston position close to the desired inner reversal point independently of the action of the reversal-related means.

16. The method of starting a free piston engine having a power cylinder with inlet and exhaust ports, a power piston freely reciprocable in the cylinder along a path between desired normal inner and outer piston reversal points which may vary from stroke to stroke- ,and adjustable combustion-causing means for igniting a combustible mixture in the power cylinder and causing successive power strokes ofthe piston toward its outer reversal point, comprising the steps of a. feeding into the power cylinder a combustible starting mixture capable of ignition at pressures substantially below the normal compression pressures of such an engine,

b. moving the power piston toward its inner reversal point to an intermediate position along its path at which the inlet and exhaust ports are at least substantially closed; and

c. igniting the combustible starting mixture as the piston moves to the intermediate position and thereby providing a combustion force causing initial movement of the power piston toward the normal outer piston reversal point to start the engine.

17. The method ofclaim 16 including the further step of adjusting said combustion-causing means after first igniting the starting mixture, and thereby causing combustion for successive transitional power strokes at points gradually shifting from said intermediate position toward the desired normal inner piston reversal point, until the combustion-causing means is causing normal operation of the engine.

Claims

1. In a free piston engine having a power cylinder with inlet and exhaust ports operable between closed and open positions in desired normal operating sequence, a power piston reciprocally movable in the power cylinder along a path between desired normal inner and outer piston reversal points which may vary from stroke to stroke, means for causing repetitive combustion in said power cylinder to drive said power piston during normal engine operation, at least one other cylinder, a second piston movable therein, and means interconnecting said power and second pistons for simultaneous reciprocal movement in their respective cylinders, the improved starting means comprising, in combination, piston-moving means for moving the power piston inwardly toward its desired normal inner reversal point from an outer preliminary starting position to an intermediate first relative position of the pistons at which the pressure in the power cylinder is substantially below the compression pressure customary in the power cylinder just prior to combustion during normal engine operation, means defining a starting combustion chamber in connection with one of said cylinders, means for supplying a combustible starting mixture to said starting combustion chamber before the pistons reach said intermediate position, spark means for igniting said starting mixture within the starting combustion chamber, and means for initially energizing said spark means as said piston-moving means moves said pistons to said intermediate first relative position and thereby causing combustion of the combustible starting mixture, the energy released by said starting mixture combustion being transmitted to one of said pistons to start rapid reciprocal movement of the power piston toward its outer desired reversal point and thereby initiate normal engine operation, and said means for causing repetitive combustion in said power cylinder during normal engine operation being thereafter operable to cause such combustion at other relative intermediate positions of the power piston at which a combustible mixture is under gradually higher and more normal compression pressures within the power cylinder during transitional operation while the engine is assuming normal operating condition and at the desired normal inner reversal point during such normal engine operation.

4. In a free piston engine having a power cylinder with fuel inlet means and exhaust means operable between closed and open positions in desired normal operating sequence, a power piston reciprocally movable in the power cylinder along a path between desired normal inner and outer piston reversal points which may vary from stroke to stroke, means for causing repetitive combustion in said power cylinder to drive said power piston during normal engine operation, at least one other cylinder, a second piston movable therein, and means interconnecting said power and second pistons for simultaneous reciprocal movement in their respective cylinders, the improved starting means comprising, in combination, means defining a starting combustion chamber in connection with one of said cylinders, means for supplying a combustible starting mixture to said starting combustion chamber, spark means for igniting said starting mixture within the chamber, and means for initially energizing said spark means at a first relative position of the pistons at which the pressure of the mixture in said starting chamber is substantially below the compression ratio customary during normal running of such engines and thereby cuasing combustion expansion of the combustible mixture, the energy released by said cumbustion expansion being transmitted to one of said pistons to start rapid reciprocal movement of the power piston toward its outer desired reversal point and thereby initiate normal engine operation, and said means for causing repetitive combustion in said power cylinder being operable to cause such combustion at other relative positions of the pistons at which a combustible mixture is under substantially higher and more normal compression pressures within the power cylinder during transitional operation while the engine is assuming normal operating conditions and during normal engine operation, said starting combustion chamber being within the power cylinder and including the portion of the power cylinder which serves as a power chamber for repetitive combustion to drive said power piston during normal engine operation, and said free piston engine having means for moving said pistons to a preliminary starting position within their respective cylinders prior to operation of the means for initially energizing said spark means, and means for moving said power piston toward its inner reversal point from said preliminary starting position to said first relative position at which the spark means is initially energized, said preliminary starting position being close to the outer desired reversal point of the power piston and said first relative position of the piston being an intermediate position in which the inlet and exhaust means are substantially closed and the combustion gases exert a substantial pressure against the power piston when ignited and drive the power piston in the direction of its desired power stroke.

6. In a free piston engine having a power cylinder with fuel inlet means and exhaust means operable between closed and open positions in desired normal operating sequence, a power piston reciprocally movable in the power cylinder along a path between desired normal inner and outer piston reversal points which may vary from stroke to stroke, means for causing repetitive combustion in said power cylinder to drive said power piston during normal engine operation, at least one other cylinder, a second piston movable therein, and means interconnecting said power and second pistons for simultaneous reciprocal movement in their respective cylinders, the improved starting means comprising, in combination, means defining a starting combustion chamber in connection with one of said cylinders, means for supplying a combustible starting mixture to said starting combustion chamber, spark means for igniting said starting mixture within the chamber, and means for initially energizing said spark means at a first relative position of the pistons at which the pressure of the mixture in said starting chamber is substantially below the compression ratio customary during normal running of such engines and thereby causing combustion expansion of the combustible mixture, the energy released by said combustion expansion being transmitted to one of said pistons to start rapid reciprocal movement of the power piston toward its outer desired reversal point and thereby initiate normal engine operation, and said means for causing repetitive combustion in said power cylinder being operable to cause such combustion at other relative positions of the pistons at which a combustible mixture is under substantially higher and more normal compression pressures within the power cylinder during transitional operation while the engine is assuming normal operating conditions and during normal engine operation, said starting combustion chamber being within the power cylinder and including the portion of the power cylinder which serves as a power chamber for repetitive combustion to drive said power piston during normal engine operation, and said free piston engine having piston positioning means for moving the power piston inwardly toward its desired inner reversal point from a preliminary starting position located outwardly beyond said first relative position, and fuel delivery means having a member operable between a starting position in which the fuel delivery means feeds a combustible auxiliary starting mixture to the power cylinder and a running position in which the fuel delivery means feeds a normal operating mixture to the power cylinder, said fuel delivery means member being selectively operable to its starting position, before said piston positioning means moves the power piston inwardly to said first relative position.

12. A free piston engine according to claim 11 having disabling means for discontinuing effective operation of said position-responsive means after the initial actuation of the ignition means.

16. The method of starting a free piston engine having a power cylinder with inlet and exhaust ports, a power piston freely reciprocable in the cylinder along a path between desired normal inner and outer piston reversal points which may vary from stroke to stroke,and adjustable combustion-causing means for igniting a combustible mixture in the power cylinder and causing successive power strokes ofthe piston toward its outer reversal point, comprising the steps of a. feeding into the power cylinder a combustible starting mixture capable of ignition at pressures substantially below the normal compression pressures of such an engine, b. moving the power piston toward its inner reversal point to an intermediate position along its path at which the inlet and exhaust ports are at least substantially closed; and c. igniting the combustible starting mixture as the piston moves to the intermediate position and thereby providing a combustion force causing initial movement of the power piston toward the normal outer piston reversal point to start the engine.

17. The method of claim 16 including the further step of adjusting said combustion-causing means after first igniting the starting mixture, and thereby causing combustion for successive transitional power strokes at points gradually shifting from said intermediate position toward the desired normal inner Piston reversal point, until the combustion-causing means is causing normal operation of the engine.