US2108890A - Motor compressor of the free piston type - Google Patents

Description

Feb. 22, 1938., H. JNICKE MOTOR COMPRESSOR OF THE FREE PISTON TYPE 2 Sheets-Sheet l www NM mw.

Filed 001'.. 2, 1935 Fe. 22, 1938. H. JNICKE MOTOR COMPRESSOR OF THE FREE PISTON TYPE 2 Sheets-Sheet 2 Filed 0G12. 2, 1935 Patented Feb. 22, 1938 UNITED sTATi-:sA

PATE

yMOTOR. COMPRESSOR (F THE FREE PISTO Y [-Hermann Jnicke, Dessau (Anhalt), Germany,

assignor to Therese Munich, Germany Application October 2, In Germany October 16, 1934 AJunkers, Gauting, near 1935, serai N. 43,1'8'1.

' 9 claims. (c1. 23o-5s) My invention relates to free piston motor compressors and more especially to that type. of engines of the kind aforesaid, in which the air compressed in the compressor is utilized to drivev the motor, forming part lof the mixture of gas and air, or to scavenge the motor cylinder.

It is an object of my invention to improve this type of motor compressor. In motor compressors, in which the pistons of the motor and the compressor are rigidly connected With each-other,

forming a freely oscillating mass system,'it hasl been suggested to regulate the compressor output at an approximately constant stroke of the freely moving mass by varying the pressures (the suction pressure or the exhaust pressure or both) prevailing in the compressor. It has also been propose-d to feed the compressed air delivered by the compressor, as a whole or partly, to

the motor as scavenging and charging air under l a comparatively high pressure, the exhaust gases (gases of combustion and scavenging air in excess) being fed to a secondary engine, for instance a piston engine or a turbine, to driveit. According to this invention now the suction and the delivery pressures in the compressor of an engine of this type are varied for the purpose of regulating the energy developed by the driving gas furnished by the motor, and this in such manner that the ratio between these two pres- -sures (which is hereinafter called the pressure ratio of the compressor)` remains at least approximately constant.

This mode of regulation of such motor compressors has the effect that the pressure ratio (scavenging and charging pressure: compression end pressure) remains also at least approximately constant. If for instance the suction pressure in the compressor is reduced, while the l pressure ratio of the compressor remains constant, the discharge pressure drops also correspcndingly. In consequence of the reduced pressures the feed-back energy liberated by the expansion of the residual compressed air in the dead space of the compressor becomes smaller also during the return stroke; however, since together with the discharge pressure of the compressor also the scavenging and charging pressures (and consequently the quantity) of the motor charge (constant charging volume times -density of the charge) had been reduced, the reduced feed-back energy still suiices to compress this reduced quantity of motor charge at about the same pressure ratio as hitherto prevailed in the motor. Since in motors with ignition by compression, as are usedas a rule for v the motor at least approximately constant, is of decisive importance for thev faultless operation.

of a free piston. motor compressor `of this type regulatable within wide'limits. f

The reduction ofthe discharge and delivery pressures and in Iconsequence also of the motor ,pressures under partial loads at the same time leads to a considerable reduction of the number of cycles of action perunit of time, i. e. to a further regulation of output of the engine, so that comparatively small 'variations of pressure will give rise to considerable variations'of the lquantity of driving gasl delivered. v -If the compressor piston has a larger diameter than the motor piston, there is provided on the rear side of the compressor piston a differential surface equal to the diiference between the surface of the compressor piston and the surface of the motor piston; the pressure acting on thisv surface results, during the return stroke, in an amount of energy taken up, by which the energy available during the return stroke for the compressioni of the motor charge is diminished. Therefore if the amountof the feed-back energy liberated in the compressor varies in consequence of regulating operations, the amount of energy piston must also be varied in the same sense in order thatl the amount of energy available for Y the compression of the motor charge enable this compression to be carried through with the desired pressure ratio which shall be kept approximately constant. Therefore, in accordance with this invention, I further provide that the suction pressure of the compressor which shall be regulated act on the rear face of the compressor piston. This pressure may either act on the piston unvariably asa constant load during the entire stroke or it may form the lower or the higher end pressure of a compression-expansion line.

I will now explain by invention in detail, having reference to the drawings annexed to this specification and forming part thereof, which illustrates in a purely diagrammatic manner an engine embodying my invention by way of example.

In the drawings f Fig. 1 shows a diagrammatic longitudinal section of a free piston motor compressor including two reciprocating free pistons, being one emdiagrams of the several compression spaces for two regulation conditions.

Fig. 6 is a section of a modified form of a separate control member.

Fig. I illustrates diagrammatically a modification being a free piston motor compressor including one reciprocating freevpiston, while Fig. 8 is a longitudinal section, drawn to a larger scale, through the motor cylinder shown in Fig. 7.

Referring to the drawings, I is the motor cylinder, in which operate two pistons 2, 2 moving in opposite directions; each of these motor pistons, one of which controls the scavenging ports 3, the other one the exhaust ports 4, is rigidly connected with the compressor piston 5. The compressor pistons operate in compressor cylinders 6 arranged coaxially to the motor cylinder I and provided with suction valves 1 and pressure valves 8.

When the two freely moving masses 2,5 have approached each other and when the quantity of charging air enclosed between the motor pistons 2 is compressed, fuel is injected into the air through the nozzle 9. Theregulation by means of a fuel pump of the quantity of fuel to be supplied to the motor may take place e. g. in a well known manner in dependency of a pressure gas container, as described in detail e. g. in the description of Fig. 1 of applicants copending U. S. application Ser. No. 710,483. Such container may be connected to conduitI I0 after the compressor portion of the free piston engine according to the present invention in a manner such that from this container the scavenging air passes into the motor cylinder. On the other hand, a pressure gas container might also be connected to the conduit 30 so that the secondary engine is supplied from this container. -The gases of combustion generated in the combustion, which now sets in, force the freely moving masses apart (working stroke). In consequence thereof there first takes place a compression of the charge enclosed in the compressor cylinders from the pres'- sure pi to pressure p2 along line AB and thereafter the discharge of the compressed air along line BC (Fig. 2). After the scavenging and exhaust ports 3, 4 have been uncovered by the motor pistons 2, the freely moving masses come to a standstill. The residual compressed air in the dead spaces of the compressor cylinder 6, on which acts the pressure p2, in expanding along line CD (Fig. 2) down to the suction pressure p1, now forces the freely moving masses again towards each other (return stroke), while at the same time (line DA) fresh air is sucked through the suction valves 1 into the compressor cylinders. The compressed air discharged during the working stroke through the pressure valves 8 flows through the pipe I0,after the scavenging ports 3 have been uncovered by one of the motor pistons 2, into the motor cylinder I, at the same time displacing the exhaust gases through the exhaust ports 4 and filling the motor cylinder with fresh air under the pressure pz. In the exhaust gas conduit I I communicating with the exhaust ports 4 of the motor is provided a pressure regulating member' 2U, which determines the scavenging pressure in the motor and consequently also the discharge pressure pz in the compressor. The waste gases and the scavenging air in excess discharged through the exhaust ports llinked to the rods 50, 5I.

4 are fed to a secondary engine, for instance a. turbine (not shown) to do useful work therein.

For the purpose of regulating the quantity and amount of energy in the driving gas furnished by the driving gas generator, the suction pressure p1 and delivery pressure p2 in the compressor are varied. For the variation of the suction pressure there is for instance provided at each suction chamber I8 of the compressor a slide I2, which is adjustable manually or automatically, for instance inv dependency from the load on the secondary engine. 'I'his is shown in Fig. 1, in which the centrifugal governor 40 of a secondary engine (not shown) is provided with a sleeve 4I, to which corresponding to the two slides I2 toward both sides two rods 42, 43 are linked. The other ends of these rods are linked to the free ends of the legs 44, 45 of the bell cranks arranged for rotation about the points 46, 41. The free ends of the legs 48, 49 of the bell cranks are These rods 50, 5I are connected through the fulcrurns 52, 53 with the rods 56, 51 guided at 54, 55, these rods being .directly connected to the slides I2. The positions of the governor and the rods, shown in full lines, illustrate the positions with higher numbers of rotation, i. e. with smaller load on the secondary engine, while on the left hand side of the governor the dashed lines indicate the positions of the governor sleeve and the rods with smaller nurnbers of rotation, i. e. with higher load on the secondary engine. In the latter case e. g. the

fulcrum 52 has been displaced toward 58. About the length of this distance 52-58 also the slide has been lifted. Hereby the throttling of the suction air has been reduced in a manner such that a higher output of the compressorportionand also of the motor portion of the free piston engine is effected'. When the inlet is throttled, i. e. when the suction pressure pi is low, there is obtained the compressor diagram A'B'C'DA' drawn with dash lines in Fig. 2, with the delivery pressure p'z. The variation of the delivery pressure in such manner that the pressure ratio inthe compressor remains approximately constant, is effected by means of the pressure regulating member 20 provided in the conduit II, which is illustrated in section in Fig. 6. The waste gas conduit II is closed by a slide 22 formed with a passage .2I, and operated by a piston 23. The gases in the conduit II pass through a boring 24 below the lower ring-shaped piston surface 25, so that this surface is acted upon by the pressure of the combustion gases escaping from the motor cylinder and of the scavenging air in excess, i. e. with the pressure pz or pz, while the upper surface 26 of the piston 23 is placed under the suction pressure p1 or pi, since the space above the piston 23 is connected through pipes 21, I1 with the suction chamber I8. The atmospheric pressure acting on the slide face 28 is counteracted by the spring 29 acting from above on the piston 23, this spring being so dimensioned that a small excess of force tends to shift the pressure regulating member 22, 23 downwardly into closing position. The surface ratio of the two surfaces 24 and 2S is so chosen that on the pressure p2 being attained, the pressure regulating member is lifted counter to the pressure p1 on the piston surface. However, if the suction pressure p1 is throttled, for instance down to p'i, the correspondingly lower delivery pressure p2 suffices already to open the pressure regulating member, so that thus the ratio of the pressures 1712172 remains always approximately constant, since the surface ratio is approximately in the reversed vproportion of these pressures.

The waste gases and the scavenging air, in

back energy, which is liberated in the compressor f cylinder and brings about the return stroke, is

represented at a high suction and delivery pres-y sure of the compressor by the surface CDAFEC and, in the case of the reduced pressures p'i, p'a, by the considerably smaller surface CDA'FEC'. According to Fig. 3 the compression in the motor cylinder begins in the f'lrstcase (high compressor pressures) at the pressure pz andends at the pressure 123, the compression work is represented by the surface GHJKG; in the second case the compression in the motor cylinder begins at the lower pressure p'z and ends at the pressure p'a; in correspondence therewith also a lower compression energy corresponding to the surface G'HJKG must be brought into action.; Thus the compression ratio inthe motor (in the first case parpz and in the second case p'3:p2) is at least approximately equal in bothcases, i. e. it

i o remains practically constant during all variations of the initial compressor pressure.

When the compressor piston 5 has a larger diameter than the motor piston 2, so-y that on the rear sideI3 of the compressor piston 5 there remains over an effective piston surface equal to the difference between the compressor piston surface and the motor piston surface, this differential surface must, during the return stroke, produce a displacement energy, which must be subtracted from the feed-back energyCDAFEC lberated in the compressor cylinder, in order to obtain the energy still available for the com-` pression of the motor charge. In order now, that in regulating steps i. e. when varying the pressures arising in the compressor and the feed-back energy to be produced by the compressor, the

` permanently constant pressure ratio in the motor be attained, I load also the diil'erential surface with a regulatable pressure, for instance the suction pressure of the compressor. In the two instances of regulation here in vview there now result, according to Fig. 4, different amounts of displacement energy to be produced by the differential surface, viz. in the first case (loading with the compressor suction pressure p1) the amount represented by the surface LMNOL, in

the second casel (loading by the compressor presj sure pi) the amount corresponding to the surface LMNOL. There are therefore available as feed-back energies: v

In the rst case:

surface CDAFEC-surface LMNOL:

surface GHJKG and In the second case:

surface CDAFECf-surface L'MNOL: surface G'H'JKG Since the amounts of energy to be deducted (LMNOL and LMNOL) vary in thesame proportion as the amounts of energy liberated in the compressor, the pressure ratio in the motor (pztpa) remains at least approximately constant. In order to realize this mode of operation, it is only necessary, in the arrangement according to Fig. l, to bring the spa-ce I4 covered by the differential surface I3 into permanent communication, by means of a conduit, with the space I8 stroke), but duringtlie inner dead centre posibetween the throttle slide I2 and the suction n valves 1.

Instead of placing on the differential surface I3 a load which remains equal throughout the stroke, according to line LM or LM, I may also rplace thereon a load which changes, according to certain laws, for instance an alternatingcompression and expansionof the gas in the. space I4 according to Fig. 5 which follows the line LQ for therst, and the line L'Q' for the second of the two regulating instances mentioned above. To this end there is connected with the compressor piston 5 a slide I9 which uncovers an aperture I6 formed in the cylinder wall, which communicates with the suction chamber I8 through the conduit I"I, when the freely mov- .ing mass has reached its extreme'iend positionv (between the end of the working stroke and the start for the return stroke). I thus obtain that in this end position the same pressure prevails in the space I4 as inthe space I8; on the apertures I 6 having been closed, when the return Astroke begins, there now takes place a compresalso one ofthe regulating pressures (either the v v suction pressure pi or the delivery pressurepz) may form the upper end pressure of a compression-expansion line. In that case the aperture I6 should be controlled in such manner that the space I4 communicates with the space I8 through conduit I'I not, as above, during the outer dead centre position of the piston (between thefend of the working stroke and the start of --the return tion (between the end of the return stroke and the start of the working stroke). However, if the delivery pressure p2 is chosen as end pressure, then during theinner dead centre position the space I4 must be made to communicate with the delivery conduit I0 of the compressor.

The quantity of fuel to `be fed per cycle into the motor cylinder through the nozzle 9, should be chosen in accordance with the `quantity of air, which is regulatable according 'to thisA invention, in the motor cylinder. 'The Aregulation of the quantity of fuel may also be inuencedin a well known manner in dependency fromthe regulating pressures (suction pressure p1 or delivery pressure p2). l

Fig. 7 illustrates diagrammatically a free piston motor compressor provided with a single reciprocatory free piston, the same reference numerals being used as in Fig. 1. According to Fig. 7, a buffer or compensating cushion chamber is provided, which comprises the piston 35 and the cylinder space 36. The space 36 constitutes a boring in the reciprocatory free piston 2, 5, while the piston 35 is stationary. The movement of the free piston 2, 5 causes the content of the cylinder space 36 to be alternately compressed and expanded. 'I'he amount of energy stored in this manner in the buffer space 36 during the working ,(upward) stroke of the motor piston 2 is again delivered during the return (downward) stroke of the piston to the free pistons, vin a manner known in itself, for the purpose of supplementing the amount of energy deriving from the dead space of the compressor.

Fig. 8 shows a longitudinal section, drawn to a larger scale, through the motor cylinder i shown in Fig. 7. `The reference numerals are the same as in Fig. 7. Two slots 3 are provided as inlet for the compressed air, while the combusted gases are delivered from the motor cylinder space iirst through the preliminary delivery slots 4' and subsequently through the main delivery slots 4. There are shown two of each of these delivery slots. The inlet and delivery slots are controlled, in a known manner, by means of the motor piston 2. Tne arrows shown in Fig. 8 represent the direction of current of the compressed air or the combusted gases, respectively.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art.

1. A free piston motor compressor, iny which the compressed air produced in the compressor serves as scavenging and charging air for the motor, comprising in combination, a motor cylinder, a compressor cylinder, a free piston in said motor cylinder and a free piston in said compressor cylinder, said pistons being rigidly connected with each other, means for conducting compressed gas from said-compressor cylinder into said motor cylinder and means for varying the suction and delivery pressures in said compressor cylinder, while keeping the ratio of the two pressures approximately constant.

2. A free piston motor compressor comprising in combination, a motor cylinder, a compressor cylinder, a free piston in said motor cylinder and a free piston in said compressor cylinder, said pistons being rigidly connected with each other, said compressor piston having a larger diameter than said motor piston, means for causing the suction pressure prevailing in said compressor to act on the rear face of said compressor piston, means for'conducting compressed gas from said compressor cylinder into said motor cylinder and means for varying the suction and delivery pressures in said compressor cylinder, while keeping the ratio of the two pressures approximately constant.

3. A free piston motor compressor comprising in combination, a motor cylinder, a compressor cylinder, a free piston in said motor cylinder and a free piston in said compressor cylinder, said pistons being rigidly connected with each other, said compressor piston having a larger diameter than said motor piston, means for causing the suction pressure prevailing in said compressor to act on the rear face of said compressor piston, means for conducting compressed gas from said compressor cylinder into said motor cylinder, means for varyingthe suction and delivery pressures in said compressor cylinder, while keeping the ratio of the two pressures approximately constant, and means for causing the pressure prevailing in the part of said compressor cylinder covered by the rear side of said compressor piston to vary according to a compression-expansion line, the initial pressure of which is determined by one of the pressures prevailing in said compressor.

4. A free piston motor compressor comprising in combination, a motor cylinder, a compressor cylinder, a free piston in said motor cylinder and a free piston in said compressor cylinder, said pistons being rigidly connected with each other, said 'compressor piston having a larger diameter than said me or piston, means for causing the suction pressure prevailing in said compressor to act on the rear face of said compressor piston, means for conducting compressed gas from said compressor cylinder into said motor cylinder, means for varying the suction and delivery pressures in said compressor cylinder, while keeping the ratio of the two pressures approximately constant, and means for causing the pressure prevailing in the part of said compressor cylinder covered by the rear side of said compressor piston to vary according to a compression-expansion line, the end pressure of which is determined by one of the pressures prevailing in said compres- SOI'.

5. A free piston motor compressor comprising in combination, a motor cylinder, a compressor cylinder and free pistons rigidly connected with each other and arranged in said cylinders for free reciprocation, said motor cylinder being formed with an exhaust port, an exhaust gas conduit arranged to the rear of said exhaust ports, a regulating device inserted in said conduit, a piston-shaped control member forming part Iof said device and formed with two piston surfaces, one surface being adapted to be acted upon by one, the other surface by the other reg- -ulating pressure arising in said engine, these controlling surfaces being dimensioned at a ratio which is approximately the reverse of the ratio of said regulating pressures.

6. A free piston motor compressor comprising in combination, a motor cylinder, a compressor cylinder and freel pistons rigidly connected with each other and arranged in said cylinders for free reciprocation, said motor cylinder being formed with an exhaust port, an exhaust gas conduit arranged to the rear of said exhaust ports, a regulating device inserted in said conduit, a piston-shaped control member forming part of said device and formed with two piston surfaces, one surface being adapted to be acted upon by one, the other surface by the other regulating pressure arising in said engine, these controlling surfaces being dimensioned at a ratio which is approximately the reverse of the ratio of said regulating pressures, and means whereby the space in said compressor cylinder covered by the rear face of said compressor piston is arranged to be permanently acted upon by the suction pressure in said compressor.

7. A free piston motor compressor comprising in combination, a motor cylinder, aV compressor cylinder and free pistons rigidly connected with each other and arranged in said cylinders for free reciprocation, said motor cylinder being formed with an exhaust port, an exhaust gas conduit arranged to the rear of said exhaust ports, a regulating device inserted in said conduit, a piston-shaped control member forming part of said device and formed with tw-o piston surfaces, one surface being adapted to be acted upon by one, the other surface by the other of the regulating pressure arising in said engine, these controlling surfaces being dimensioned at a ratio which is approximately the reverse of the ratio of said regulating pressures, and a controlling member connected with said pistons and connecting the space in said compressor cylinder covered by the rear face of said compressor piston during the outer dead centre position of said piston with the suction space of said compressor.

8. A free piston motor compressor comprising in co-mbination, a motor cylinder, a compressor cylinder and free pistons rigidly connected with each other and arranged in said cylinders for free reciprocation, said motor cylinder being formed with an exhaust port, an exhaust gas conduit arranged to the rea .r of said exhaust ports, a regulating device inserted in said conduit, a piston-shaped vcontrol member forming part of said device and formed with two piston surfaces, one surface being adapted to be acted upon by one, the other surface by the other regulating pressure arising in said engine, these controlling surfaces being dimensioned at a ratio which is approximately the reverse of the ratio of said regulating pressures, and a control member, which connects the space in said compressor cylinder covered by the rear face of said compressor piston during the inner dead centre position of said piston with the suction space of said compressor 9. A free piston motor compressor comprising in combination, a motor cylinder, a compressor cylinder' and free pistons rigidly connected with each other and arranged in said cylinders for free reciprocation, said motor cylinder being formed with an exhaust port, an exhaust gas conduit arranged to the rear of said exhaust ports, a regulating device inserted in said conduit, a piston-shaped control member forming part of said device and formed with two piston surfaces, one surface being adapted to be acted upon by one, the other surface by the other regulating pressure arising in said engine, these controlling surfaces being dimensioned at a ratio which is approximately the reverse of the ratio of said regulating pressures, and a control member, which connects the space in said compressor cylinder covered by the rear face of said compressor piston during the inner dead centre position of said piston with the delivery conduit of the compressor.

HERMANN JNICKE.

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