US2867374A - Means for starting internal combustion engines of the opposed piston type - Google Patents

Description

Jan. 6, 1959 PETERSEN 2,867,374

MEANS FOR STARTING INTERNAL COMBUSTION ENGINES OF THE OPPOSED PISTON TYPE Filed July 16, 1954 2 Sheets-Sheet 1 Fig.3

AWE/viola HA Ms PETER-551V A'r-roRN Y Jan. 6, 1959 H. PETERSEN 2,857,374

MEANS FOR STARTING INTERNAL COMBUSTION ENGINES OF THE OPPOSED PISTON TYPE Filed July 16, 1954 2 Sheets-Sheet 2 Fig.4

Fig. 3a

1% N5 757525 EN 5, idl 5 @6 2? United States Patent MEANS FOR STARTING INTERNAL COMBUSTION ENGINES OF THE OPPOSED PISTON TYPE Hans Petersen, Surth (Rhine), Germany Application July 16, 1954, Serial No. 443,948

Claims priority, application Germany June 27, 1953 7 Claims. (Cl. 230-56) This invention relates to means for starting internal combustion engines having opposed pistons. More particularly, the invention relates to the starting of such engines by means of a compressed gas suflicient for one starting stroke in respect to pressure and quantity.

Conventionally, engines of the opposed piston type are started by manually opening a valve of a container in which the compressed gas, under a predetermined pressure and in a predetermined volume found to be that required for a single starting stroke, is stored. The pistons, when in their starting position, are directly impinged upon by the compressed gas.

An undesirable feature of this arrangement resides in the fact that it is practically impossible'to operate the starting valve by hand with sufiicient speed to expose im-' mediately the entire cross-section of .the passage, so that the opposed pistons may be impinged upon with 'a' shock like force, under full pressure... In consequence, the pistons, asjsoon as they overcome the staticfriction start to move when the valve is only partly open-,., that is, before the entire cross-section of-'. the passage of. the starting valve has been .exposed' and the-pressure. has been fully built up back of the piston. Hence, the full force of the compressed gas necessary for moving the piston through its first working stroke, is not available in time. Under these circumstances, the engine does not start.

Devices are also known whereby the starting valve will be opened by a suitable mechanical or pneumatic means with a shock-like force, so that the opposed pistons will be impinged upon immediately by the full concentration of compressed gas. However, great ditficulties are encountered in designing such starting valves so that they operate safely, since very great forces occur during the action, which forces must be taken up in some way.

Another starting means has also been proposed in which one or more of the pistons of the cylinders are impinged upon by compressed gas. \First, a space outside the cylinder is filled with the starting gas. At this time, the pistons are in a starting position and prevent admission of the gas to the cylinders. When the desired starting pressure has been reached, the pistons are moved by a special device a distance such that they admit the starting air or other gas from the charged space to the cylinders.

Thus, the starting requires two separate operations which take place one after the other. In the first operation, the starting space outside the cylinder, in which the energy necessary for one starting stroke is stored, is charged with a gas under suitable pressure by opening a valve normally closing a starting container. Simultaneously, via the starting space or spaces, the areas behind the pressure valves of the cylinder are charged to working pressure. This is done in order to insure the maintenance of pressure necessary for keeping the engine running. After this step has been completed, the second step takes place. A small amount of starting air is caused to enter in the rear of the pistons by means of a 2,867,374 Fatented Jan. 6, 1959 'ice special device in order to initiate the starting movement of the pistons, and to move them a distance suflicient for them to admit the starting air from the filled starting spaces to the cylinders.

This method of starting is deficient due to the fact that the pistons, in the starting position, do not completely prevent admission of the starting air to the cylinders. During the first step, small quantities of starting air enter the area at the rear of the pistons from the spaces outside the cylinders while said spaces are being charged, leakages between piston and cylinder being um avoidable. As a result, the pistons start to move after having overcome the static friction before the spaces outside the cylinders are charged to full operating pressure.

The present invention has as an important object the elimination of the above described deficiencies.

According to the invention an essential feature of the starting means is a two-phase impingement of the compressed gas upon the opposed pistons. The arrangement is characterized by the fact that the phases are initiated at different times, with the one phase changing into the other. In the first phase, i. e. the initiating of the starting stroke, the movement of the opposed pistons is started by a throttled impingement of the compressed gas on the pistons, caused by throttle bores or other throttling means, which e. g. may be a piston ring slot. In the second phase, i. e. the starting stroke proper, the opposedpistons are impinged upon by the gas under full pressure, through lateral slots arranged in the cylinder walls of the starting stroke spaces.

The two-phase operation is initiated by the opening of a starting valve actuatedmanually, mechanically, pneumatically or hydraulically, whereby the compressed gasesare adrnitted into the starting conduits from a start-ing container which will have been pro-charged with gas under a selected pressure and in a predetermined quantity.

In order to prevent the pistons from beginning their movement before the starting valve is fully opened and the entire cross-sectional area of the passage is exposed, and in order to have fully available the pressure and quantity of the compressed starting gas needed for the starting stroke, the entrance of the gas into the piston cylinders is slowed under rigidly controlled conditions.

This is accomplished by virtue of the fact that in the starting position of the pistons, the main entry ports of the cylinders are covered by the opposed pistons, whereas the starting gas supply conduits are kept in full and constant communication with the interiors of the cylinders by the throttle bores or other throttling means. As a result, the compressed gas first enters the cylinder through the throttle bores, in small quantities only. At this stage, the main entry ports are sealed, in the initial or starting position of the pistons, against pressure losses, by disposition of the piston rings of the opposed pistons on both sides of said ports in the longitudinal direction of the cylinder.

The throttle bores or other throttling means are so dimensioned as to cross-sectional area that, in the first phase of the starting operation, the building up of the pressure in the cylinders in the rear of the opposed pistons, and the movement of the pistons up to the full opening of the main ports, will not be completed before the manually operable starting valve, which closes the starting container is fully opened, and the pressure at the starting slots or main ports is equal to the pressure in said container.

The throttling bores or other throttling means may be formed in interchangeable inserts screwed into or otherwise removably attached to the cylinder or pistons, whereby the size of the throttle bore or other throttling means may be adjusted as desired.

The entrance of the compressed gas into the cylinder during the second phase of the starting operation will be controlled by the opposed pistons proper, in that the latter pass over andthus uncover the starting slots or ports. at a predetermined time. At this time the cross-sectionalareas of the inlets into the cylinder become so large that full pressure is present in the cylinder when the starting slots are fully uncovered. Consequently, equalization of pressure occurs throughout the entire compressed gas starting system before the gas begins to expand.

In the second phase adiabatic expansion of the gas to atmospheric or scavenger air pressure takes place, the cross-sectional areas of the passages defined by the starting slots being so dimensioned that no throttling occurs, while in each position of the opposed pistons equal pressure prevails in all spaces in which the expansion takes place. In order to permit the gas to leave the cylinder, slots are provided in the cylinder Walls at the end of the expansion stroke, which slots connect the starting stroke space of the cylinder with atmosphere or with a receiver for scavenger air. In the latter case, the compessed gas passes under pressure from the starting cylinder into the receiver, and charges the receiver partly or entirely up to operating pressure.

In order to fill the scavenger air receiver with fresh air, thereby to clear the internal combustion cylinder of exhaust residues prior to the starting of the engines, it is advisable to provide the opposed pistons with throttle bores in such a manner that in the starting position, the throttle bores connect the scavenger air receiver with the starting conduits. The compressed air for starting the engine can be taken in a manner known per se from a compressed air bottle, which may be charged by a compressor driven by the opposed piston machine.

The compressed gas bottle, the contents of which sufiice for repeated or successive starting of the machine, may also be charged by compressed gas from the internal combustion cylinder, in which event the compressed gas is taken from the cylinder below the inner dead center position of the internal combustion piston. Thus, the compressed gas is taken in small quantities on each stroke, before the compression end pressure has been reached, and partly after completed combustion, during the expansion of the gas.

The starting, according to the process hereinbefore described, can be accomplished on the side of the motor as Well as on the side of the compressor, and the motor cylinder scavenger pump, one or more compressor stages, and/or special butters may be used as starting stroke spaces.

In the starting of opposed piston engines on the motor side, the energy of motion of the opposed pistons, caused by the starting compressed gas, will first be stored in the compressor stages or in separate butters. After the reversal of the direction of movement, these energies cause the return movement of the opposed pistons and the compression of the charge of the motor cylinders to ignition temperature.

If the compressor cylinders are used as starting'stroke spaces, they can be in continuous communication with a starting space or spaces located exteriorly of the compressor cylinders, by means of starting slots arranged in the cylinder walls, without requiring the mounting of a special starting valve therebetween. The starting pres sure gas will be directed in selected pressure and quantity into the mentioned starting space or spaces. In the starting position, the compressor pistons cover the starting slots and prevent larger quantities of compressed gas from entering the starting stroke spaces. Communication of the starting stroke spaces with the atmosphere by means of venting valves prevents pressure from building up in the rear of the compressor pistons, which may otherwise occur owing to the entrance of small quantities of compressed gas from the starting spaces located outside the compressor cylinder, into the starting stroke spaces proper within the cylinder. Thus, the compressor pistons are prevented from starting to move prematurely.

While the venting valves-are open, the starting spaces outside of the compressor cylinder and also the spaces in the rear of the pressure valves of the compressor stages will first be filled with starting air while the compressor pistons remain in the starting position, the starting slots being covered.

Only after this step will the starting process proper be initiated, by closing of the venting valves arranged in the starting stroke spaces. In consequence, pressure will now build up in the rear of the compressor pistons, whereby the beginning of the movement of the opposed pistons will be initiated and the starting operation according to the two phase process will be accomplished.

In the drawing forming a part of this application, like reference numerals designate like parts throughout. In said drawing:

Fig. 1 is a section of a part of a starting cylinder equipped for the starting process, the illustrated position of the piston showing the inner dead center position and further constituting the starting position,

Fig. 2 is a diagrammatic view showing the theory of the starting operation,

Fig. 3 is a largely diagrammatic illustration showing the application of the invention to a single stage internal combustion engine-air compressor,

Fig. 3a is a fragmentary, diagrammatic illustration, on an enlarged scale, of certain details of the compressor cylinder structure shown in Fig. 3, and

Fig. 4'is a view similar to Fig. 3 showing the starting arrangement for a two-stage internal combustion engineair. compressor.

7 In Fig. 1, a reciprocating piston 91 is provided in a starting cylinder 92, in a starting position. Starting slots or'main gas entry ports 93 are covered by piston 91 in the starting position. Piston rings 94 and 95 extend about the'piston 91, at both sides of the slots 93. A throttle bore 97 is provided in the starting cylinder 92 for the entrance of the compressed gas into a starting clearance space 96. Discharge slots 98 are provided for the discharge of the expanded starting air at the end of the expansion stroke.

Fig. 2, which is a pressure-volume diagram, shows the change of pressure during the passage of time in the starting process, by the diagram area ABCDEFGI-I. In the position A piston 91 is in the starting position. During the first phase of the starting process, compressed air enters the starting or clearance space 96 through the throttle bore 97 in the starting cylinder 92. The throttled impingement of the compressed gas on the piston 91 is represented by the distance AB in the diagram.

If the pressure is reached at point B the static friction of piston 91 in the starting'cylinder 92 will be overcome and the piston will start to move. The stroke initiating the starting, characterized by the distance BC in the diagram, is finished at the point C and thus the first phase of the starting process is completed. On reaching point C piston 91 passes the starting slot 93 in the starting cylinder 92 and a rapid pressure rise occurs which is illustrated in approximation by the distance CD in the diagram. A sudden acceleration is imparted to the piston 91 While the compressed gas expands adiabatically in cylinder 92. This occurrence is illustrated by the distance D-E. When thepiston 91 reaches the point E it passes over the discharge slot 98 in cylinder 92 and the compressedair leaves the latter under a sudden pressure drop illustrated by the distance BF. Over the distance F-G the starting stroke space is in communication with atmosphere or with a scavenger air receiver. At point G piston 91 has reached its end position, at which the second phase of the starting operation is completed. The return stroke of the piston 91 is then caused by the combustion occurring in'the cylinder of the internal combustion engine.

Fig. 3 shows, by way of example, a single stage internal combustion engine-air compressor of conventional design. The pistons 1 and 2, and 3 and 4, are arranged in the cylinders 5 and 6, respectively, so as to operate in opposite directions. The pistons 1, 2, 3 and 4 have enlarged portions 101, 102, 103 and 104, respectively,

which move in correspondingly shaped continuations of the cylinders 5 and 6, respectively. The pistons 1 and 3 are movably connected by connecting rods 7 with rocking lever 8, and the pistons 2 and 4 are connected by connecting rods 7 with the reciprocating lever 9.

The levers 8 and 9 are pivoted upon pins 10, 11, respectively, in housing 12. It will further be noted that the levers are connected to one another by means of a synchronizing rod 13. Rod 13 is pivotally connected at its opposite ends to the levers, eccentrically with respect to the pivot points of the levers.

As a result, synchronized movement of the pairs of pistons is insured. A common stroke chamber 14 is defined between the oppositely movable pistons 1 and 2.

is provided with inlet slots 15, outlet slots 16, and injection nozzles 17. Of larger diameter than the chamber 14 are the cylinder spaces 18, 19, said spaces having a diameter equal to the diameter of the enlarged portions 101, 102 of the pistons. Spaces 18, 19 are designed as scavenger and charging pumps, and are provided with suction valves 20, 21, respectively, and pressure valves 22, 23, respectively.

The interior of the housing serves as a scavenger air receiver 24, and is sealed against communication with the atmosphere by housing covers 25, 26.

A common stroke space 27 is defined between the oppositely movable pistons 3 and 4. This constitutes a first compressor stage, and is equipped with a suction valve 28 and a pressure valve 29. Spaces 30, 31 analogous .to spaces 18, 19, serve as buffer spaces, and also con- .stitute starting stroke spaces.

' During the starting operation, stroke spaces 30, 31 are respectively connected to the outlet ends of the branches of a starting conduit 36, by means of inlet slots or main gas entry ports 32, 33, respectively, throttling bores 132 and 133, respectively, and automatic starting valves 34, 35. In addition, the stroke spaces 30 and 31 are connected with the scavenger air receiver 24, so as to communicate therewith, by means of discharge slots 37, '38, the communication of spaces 30 and 31 with the receiver occurring at the outer dead center position of the pistons 3 and 4, respectively.

Also included in the construction is a compressed gas bottle 39 having valves 40, 41, a reduction valve 42, a starting container or reservoir 43, and a hand-actuated starting valve 44 provided with a hand lever 45. The .compressed gas bottle 39 is connected in communication with the starting container 43 by a line 46, and the starting'container 43 and the starting valve 44 communicate with one another through the medium of a pipe line 47.

Extending from stroke space 14 to the bottle 39 is a line 49, through which pressure gases travel from the stroke space 14 during the compression and expansion strokes of pistons 1 and 2, said gases being thus transferred from the space 14 to the bottle. A valve 48 is provided in line 49.

In order to move the pistons 1, 2, 3 and 4 into their starting positions, a lever 50 is provided, which is removably attached to a non-circular extension 51 of the pin of lever 8.

in comparing Fig. l with Fig. 3, it will be noticed that the elements 91, 92, 93, 96, 97 and 98 of Fig. 1 correspond to the parts 104, 12, 33, 31, 133, and 38, respectively. The arrangement on the side of piston 3 with respect to the starting slots 32 and 132, the space 30 and the discharge slot 37 is a mirror image of the arrangement of the corresponding elements on the side of piston at their confronting ends.

corresponding First, lever 50 is manually swung to shift pistons 1,

2, 3 and 4 into their starting positions. For this purpose, the stroke spaces 30 and 31 may be vented in any suitable manner not specifically illustrated.

The starting positions will have been reached when pistons 3 and 4 in cylinder 6 abut against one another In this position of the parts, lever 50 is removed. Now, the valve 41 is opened and container 43 will be charged to starting pressure through reduction valve 42 and line 46. Fuel is injected by a suitable fuel pump, not shown, through injection nozzle 17 into the stroke space 14 of the internal combustion cylinder 5.

Starting valve 44 is now opened by means of lever 45. As a result, gas flows from container 43 through valve 44, line 36, and valves 34, 35, to the throttle bores 132 and 133, and the inlet slots 32 and 33. Both the throttle bores and the inlet slots are in communication with the outlet ends of the branches of line 36.

Thereafter, the two phase starting operation will take place in the manner described hereinbefore with respect to Figs. 1 and 2. As a result, pistons 3 and 4 will initially be moved to uncover inlet slots 32 and 33. As soon as the slots are uncovered, gas flowing therethrough will impinge upon the pistons 3 and 4, and the pistons will thereupon be urged apart with high acceleration, simultaneously with movement of pistons ,1 and 2 toward one another.

The air contained in the stroke space 14 will now be compressed to ignition temperature. Immediately before pistons 1 and 2 reach their inner dead center positions, fuel will be injected through nozzle 17 into space 14. Combustion thus occurs in space 14, causing pistons and 2 to be again forced apart. Air will, as a result, be sucked from atmosphere through suction valves 20 and 21 into stroke spaces 18, 19.

While the pistons 1 and 2 are urged apart, pistons 3 and 4 move into their inner dead center position once again. Accordingly, the air contained in spaces 30 and 31 will be compressed, causing valves 34, 35 to close. Passage of the compressed air into the line 36 will, as a result, be prevented. The air compressed in stroke spaces 30. and 31 will cause the return movement of the pistons 3 and 4, and 1 and 2. I

During the movement of pistons 3, 4 toward one another, the air contained in the stroke space 27 is compressed, and isv forced outwardly through pressure valve 29, into pressure conduit 52, which leads to a compressed air receiver, not shown.

With pistons 3, 4 in their inner dead center positions, pistons 1 and 2 are in their outer dead center positions, and inlet slots 15 and discharge slots 16 are open, for the scavenging of internal combustion chamber 14. On reversal of the direction of movement, the compressed air contained in spaces 31), 31 will expand and will transmit its energy to pistons 3 and 4. Air 'is, accordingly, sucked into stroke space 27 of cylinder 6 by means of inlet valve 23, during the outward movement of the pistons 3, 4.

On movement of pistons 1 and 2 toward one another, the air drawn into the stroke spaces 18, 19, will be compressed and will be discharged into the scavenger air receiver 24, through the pressure valves 22, 23. In cylinder 5, however, the air will be compressed in stroke space 14 to ignition temperature. The subsequent working stroke accordingly repeats itself, in the manner hereinbefore described.

After the engine has been started, the valve 44, as well as valve 41 of the bottle 39 will be again closed. Subsequently, during operation of the engine, bottle 39 is recharged through valve 48 and conduit 49, from the stroke space 14, in the manner previously described. When bottle 39 is again fully charged, valve 40 will be closed and sufficient energy for another starting of the engine is thus stored.

In Fig. 4 the starting means constituting the present invention is illustrated in an application to a two stage compressor having opposed pistons of conventional design.

In this arrangement, space 14, having inlet slots 15 and discharge slots 16, and charged with fuel through nozzle 17, is provided in the same manner, in an internal combustion engine, as previously described with reference to Fig. 3. Further, as in Fig. 3, stroke spaces 18 and 19, having suction valves 20 and 21 and pressure valves 22 and 23, are designed as scavenger pumps.

In the Fig. 4 embodiment of the invention, stroke spaces 30a and 31a are provided as first compressor stages. These spaces further serve as starting stroke spaces. As in the previous form described, slots 32, 33 are normally covered by pistons 3 and 4.

At the end of the expansion stroke of the pistons, spaces 30a, 31a communicate with slots 37 and 38, which slots connect the stroke spaces 30a, 31a, in the outer dead center piston positions, with the scavenger air receiver 24. Further, stroke spaces 30a, 31a are connected in communication with each other, through a compensating conduit 52 and bores 53, 54. In conduit 52 a venting valve 55 is provided, which comprises the starting valve means in this embodiment of the present invention and can be opened and closed by actuating starting lever 56. When venting valve 55 is opened, conduit 57 connects the compensating conduit 52, and thus the stroke spaces 30a, 31a, in communication with the atmosphere.

Exteriorly of compressor cylinders 58, 59, there are provided annular spaces 60, 61 which store the compressed air or gas needed to start the engine, and in which is stored the return movement energy of the piston pairs 1, 3 and 2, 4, i. e., the energy needed in order to force pistons 3 and 4 apart and the pistons 1, 2 toward each other.

In addition, suction valves 62, 63, and pressure valves 64, 65, are provided in spaces 60 and 61. Said spaces or chambers are further connected in communication with an intermediate cooler 68, through conduits 66, 67.

The cooler is in communication with stroke space 73 of the second compressor stage, through conduits 69, 70 and slots 71, 72. Space 73 is provided with a suction valve 74, and with a pressure valve 75. Further, space 73 is in communication, on its suction side, with the atmosphere, through the medium of conduit 76. On the pressure side of space 73, on the other hand, the pressuremaintaining valve 77 is mounted, back of valve 75. Space 78, in which compression thus occurs, is of small dimensions, being so proportioned in terms of its area as to cause full operating pressure to be maintained therein on each working stroke of pistons 3 and 4. Due to this arrangement, the maintenance of pressure necessary to.

keep the engine in operation is insured in space 73. A conduit 7 9 leads to a compressed air container, not shown. Spaces 60, 61 are further connected with a reduction valve 82 through the medium of conduits 80, 81. Valve 82, in turn, is connected in communication with a compressed gas bottle 84 through the medium of a pipe 83. Compressed air is taken from this bottle by means of a stop valve 85.

As in the form of the invention shown in Fig. 3, the compressed gas bottle 84 is charged with combustion gases or compressed combustion air from stroke space 14 through valve 48, conduit 49, and stop or control valve 40.

In the Figure 4 embodiment, the starting operation occurs in the following manner:

First, lever 50 is manipulated to shift pistons 1, 2, 3 and 4 into their starting positions. In these positions, slots 32 and 33 are covered by pistons 3 and 4. Venting valve 55 is now opened by operation of lever 56.

Stop valve 85 of bottle 84 is now opened to permit compressed gases to pass through conduit 83, reduction valve 82, and conduits 80, 81 into the chambers 60, 61. The gas passes from said chambers into the intermediate cooler 68 by way of the pressure valves 64, 65 and conduits 66, 67. The gas then reaches slots 71 and 72 of cylinder 6 through pipe lines 69, 70. In this way, as a first step, the chambers 60, 61 and 68, and the conduits 66, 67, 69 and 70, disposed exteriorly of compressor cylinders 58 and 59, are charged to an operating pressure while pistons 1, 3 and 2, 4 remain in the starting position. During this stage of the operation, small quantities of compressed gas enter stroke spaces 30a and 31a through slots 32 and 33 and also through slots 71 and 72, owing to a necessary piston clearance or piston ring gaps. These quantities pass to the atmosphere through bores 53 and 54, compensating conduit 52, the open venting valve 55, and conduit 57. In this manner, pressure is prevented from building up in the rear of pistons 3 and 4 in stroke spaces 30a and 31a. Thus a premature initiation of the starting movement of the pistons is avoided during the charging of the designated spaces and conduits with compressed gas.

As a next step, fuel is injected by means of a plurality of strokes of a hand-operated fuel pump, not shown, through injection nozzle 17 into stroke space 14 of the internal combustion engine. Then, venting valve 55 is closed by starting lever 56. In this way, the parts are prepared for the starting operation hereinbefore described, with the two phase impingement of the gases upon the pistons being initiated by the slow pressure build-up in stroke spaces 30a, 31a due to leakage past the pistons, subsequent freeing of the slots or apertures 32, 33 enabling the compressed gas to flow rapidly from the annular spaces or reservoir means 60, 61 into the stroke spaces so as to cause rapid completion of the starting stroke.

It will be apparent to those skilled in the art, that many alterations and modifications of the structure hereinbefore described and illustrated are possible without departure from the spirit and essence of the invention which for that reason shall not be limited but by the scope of the appended claims.

I claim:

1. A starting device for a free motor piston machine, comprising compressor cylinder means, a pair of free compressor pistons reciprocally movable in opposite directions in said compressor cylinder means and constructed for driving connection to the motor piston means of said machine, each of said compressor pistons when in its inner dead center position defining with a respective end portion of said compressor cylinder means a corresponding starting stroke space, each of said respective end portions of said compressor cylinder means being provided with at least one starting aperture positioned to be obturated by the associated compressor piston when the same is in said inner dead center position thereof, reservoir means in communication with said starting apertures and constructed to contain at a predetermined operating pressure a quantity of compresser gas sufficient for only one starting stroke of said compressor pistons, said compressor cylinder means defining additionally from said reservoir means to each of said starting stroke spaces a flow path of substantially restricted cross-section relative to said starting apertures, and starting valve means communicating with said starting stroke spaces and operable to control the build-up of pressure in said starting stroke spaces, whereby upon operation of said starting valve means to permit a pressure buildup in said starting stroke spaces, compressed gas flows from said reservoir means via said flow path into said starting stroke spaces at a relatively slow rate determined by the restricted crosssection of said flow path to slowly initiate said pressure build-up and thus said starting stroke of said compressor pistons, while upon continued movement of the latter during said starting stroke thereof in said compressor r 9 cylinder means, said starting apertures are freed and said compressed gas then flows from said reservoir means via said starting apertures into said starting stroke spaces at a relatively high rate determined by the relatively larger cross-sections of said starting apertures to thereby effect a rapid pressure build-up and subject said compressor pistons substantially immediately to the full operating pressure so as to rapidly complete the starting stroke of said compressor pistons.

2. A starting device for a free motor piston machine, comprising compressor cylinder means, a pair of free compressor pistons reciprocally movable in opposite directions in said compressor cylinder means and constructed for driving connection to the motor piston means of said machine, each of said compressor pistons when in its inner dead center position defining with a respective end portion of said compressor cylinder means a corresponding starting stroke space, each of said respective end portions of said compressor cylinder means being provided with a first aperture positioned to be obturated by the associated compressor piston when the same is in said inner dead center position, each of said respective end portions of said compressor cylinder means being further provided with a second aperture substantially restricted in cross-section relative to the associated first aperture and communicating with the corresponding starting stroke space, a container for compressed gas constructed to contain at a predetermined operating pressure a quantity of compressed gas sufiicient for only one starting stroke of said compressor pistons, conduit means establishing communication between said container and said apertures in each of said end portions of said compressor cylinder means, starting valve means arranged in said conduit means and operable when closed to inhibit flow of compressed gas through said conduit means, and check valve means arranged in said conduit means for permitting fiow of compressed gas only in the direction from said container to said apertures, whereby upon opening of said starting valve means with said compressor pistons in their dead center positions, compressed gas flows from said container through said conduit means past said check valve means and via said second apertures into said starting stroke spaces at a low rate determined by the restricted cross-sections of said second apertures to initiate slowly the starting stroke of said compressor pistons, while upon continued movement of said compressor pistons during said starting stroke thereof said first apertures are freed and gas then flows via said first apertures into said starting stroke spaces at a relatively high rate determined by the relatively large cross-sections of said first apertures for subjecting said compressor pistons substantially immediately to the full operating pressure so as to complete very rapidly the starting stroke of said compressor pistons.

3. A starting device according to claim 2, said free motor piston machine including motor cylinder means, and a pair of motor pistons reciprocal in said motor cylinder means between inner and outer dead center positions, said device further comprising a reserve bottle for compressed gas, additional conduit means establishing communication between said reserve bottle and said container on the one hand, and between said reserve bottle and said motor cylinder means at a point in the latter below the inner dead center position of said motor pistons on the other hand, a reducing valve controlling said additional conduit means between said reserve bottle and said container, and a tapping valve controlling said additional conduit means between said reserve bottle and said motor cylinder means, whereby said bottle is charged with compressed gas taken from said motor cylinder means during operation of said machine, which compressed gas may thereafter' be introduced into said container for a subsequent starting operation.

4. A starting device according to claim 3, further comprising a scavenger air receiver communicating with said motor cylinder means, said compressor cylinder means being provided with respective outlet apertures disposed remote from said first and second apertures and positioned to be traversed by said compressor pistons during said starting stroke thereof, whereby upon termination of the movement of said compressor pistons from said inner dead center positions thereof said outlet apertures establish communication between said scavenger air receiver and said compressor cylinder means to permit compressed gas introduced into said starting stroke spaces to escape into said scavenger air receiver so as to charge the latter at least partly to its operating pressure.

5. A starting device for a free motor piston machine, comprising compressor cylinder means, a pair of free compressor pistons reciprocally movable in opposite directions in said compressor cylinder means and constructed for driving connection to the motor piston means of said machine, each of said compressor pistons when in its inner dead center position defining with a respective end portion of said compressor cylinder means a corresponding starting stroke space, each of said respective end portions of said compressor cylinder means being provided with a plurality of starting apertures positioned to be obturated by the associated compressor piston when the same is in its inner dead center position, each of said starting stroke spaces being normally vented to the atmosphere, venting valve means communicating with said starting stroke spaces and operable when closed to interrupt the venting of said starting stroke spaces, means surrounding said respective end portions of said compressor cylinder means and defining about said starting apertures a pair of annular spaces adapted to contain at a predetermined operating pressure a quantity of compressed gas sufficient for only one starting stroke of said compressor pistons, intermediate container means communicating with said annular spaces and said compressor cylinder means, check valve means arranged between said annular spaces and said intermediate container means for permitting flow of compressed gas' only in the direction from said annular spaces to said container means, and conduit means in communication with said annular spaces to supply the same with compressed gas until the latter is at said operating pressure within said container means and said annular spaces, whereby upon closing of said venting valve means with said compressor pistons in their inner dead center positions, compressed gas leaks from said container means and said annular spaces past said compressor pistons, due to clearance between the same and said compressor cylinder means, into said starting stroke spaces at a low rate determined bythe restricted dimensions of said clearance to build up the pressure in said starting stroke spaces and to initiate slowly the starting stroke of said compressor pistons, while upon continued movement of said compressor pistons during said starting stroke thereof said starting apertures are freed and said compressed gas then flows from said annular space via said starting apertures into said starting stroke spaces at a relatively high rate determined by the relatively larger cross-sections of said starting apertures for subjecting said compressor pistons substantially immediately to the full operating pressure so as to complete very rapidly the starting stroke of said compressor pistons.

6. A starting device according to claim 5, said free motor piston machine including motor cylinder means and a pair of motor pistons reciprocal in said motor cylinder means between inner and outer dead center positions, said device further comprising a reserve bottle for compressed gas,'said conduit means being connected to said reserve bottle, a reducing valve controlling said conduit means between said bottle and said annular spaces, additional conduit means establishing communication between said reserve bottle and said motor cylinder means at a point in the latter below the inner dead center position of said motor pistons, and a tapping valve controlling said additional conduit means, whereby said bottle is charged with compressed gas taken from said motor cylinder means during operation of said machine, which compressed gas may thereafter be introduced into said annular spaces for a subsequent starting operation.

7. A starting device according to claim 6, further comprising a scavenger air receiver communicating with said motor cylinder means, said compressor cylinder means being provided with respective outlet apertures disposed remote from said starting apertures and positioned to be traversed by said compressor pistons during said starting stroke thereof, whereby upon termination of the movement of said compressor pistons from said inner dead center positions thereof said outlet apertures establish communication between said scavenger air receiver and said compressor cylinder means to permit compressed gas introduced into said starting stroke spaces to escape into said scavenger air receiver so as to charge the latter at least partly to its operating pressure.

References Cited in the file of this patent UNITED STATES PATENTS 351,657 Schofield Oct. 26, 1886 2,101,159 Stevens Dec. 7, 1937 2,222,260 Janicke Nov. 19, 1940 2,306,978 Pateras Pescara Dec. 29, 1942 2,334,688 Norton Nov. 16, 1943 2,408,031 Beale Sept. 24, 1946 2,423,720 Mullejans et a1. July 8, 1947 2,585,940 Juilfs Feb. 12, 1952 FOREIGN PATENTS 541,779 Great Britain Dec. 11, 1941

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