Engine-compressor type machine

Feb. 20, 1968

j. s. Campbell 3,369,733

ENGINE-COMPRESSOR TYPE MACHINE

Filed Nov. 1, 1965

Sheets-Sheet 1

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3,369,733

J. S. CAMPBELL

ENGINE-COMPRESSOR TYPE MACHINE

Feb. 20, 1968

Filed Nov. 1, 1965

Sheets-Sheet 2

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Feb. 20, 1968 j. _s. Campbell 3,369,733

ENGINE-COMPRESSOR TYPE MACHINE

Filed Nov. 1, 1965 _{5 Sh}eets-Sheet 3

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Feb. 20, 1968 j. _s Campbell 3,369,733

ENGINE-COMPRESSOR TYPE MACHINE

Filed Nov. 1, 1965 5 Sheets-Sheet 4

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PATENT AGENT

Feb. 20, 1968 j. _s. Campbell 3,369,733

ENGINE-COMPRESSOR TYPE MACHINE

Filed Nov. 1, 1965 5 Sheets-Sheet 5

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PATENT AGENT

United States Patent Office' . ³·³⁶⁹·⁷³³

Patented Feb. 20, 1968

3,369 733 ENGINE-COMPRESSOR TYPE MACHINE James S. Campbell, Kingston, Ontario, Canada, assignor to Free Piston Development Co., Ltd., Kingston, Ontario, Canada

Filed Nov. 1, 1965, Ser. No. 505,914

Claims. (Cl. 230—56)

ABSTRACT OF THE DISCLOSURE

A compressor having in a single engine cylinder a pair of opposed engine pistons connected directly to compressor pistons in compressor cylinders disposed at opposite ends of the engine cylinder. A pair of rocker beams each pivoted at one end to a framework of the compressor and connected at the opposite end to one each of the engine pistons by piston rods is connected by a pair of connecting rods to a synchronizing crankshaft which is provided with auxiliary component drive means.

This invention relates to an engine-compressor type machine which has a compressor piston connected directly to an engine piston which is also linked to a synchronizing crank.

In compressor installations requiring relatively high pressure and/or high output flows, the normal commercial arrangement has in the past used a compressor driven through a crankshaft by a multi-cylinder diesel engine. This known arrangement is large and heavy, and in the respect that it requires conversion from translational to rotational and back to translation motion, it is inefficient. Moreover, the use of a heavy power transmitting crankshaft produces unbalance of the reciprocating masses coupled with piston side loading. Further, the unbalance makes the arrangement prone to vibration.

In the internal combustion engine field the advantage of greater output for size in a two-cycle engine over a four-cycle engine is well known, and accordingly, there are advantages in using the lighter and, in some respects, less complicated conventional, two-cycle, opposed piston diesel engine in a compressor unit. However, in such an engine there is the need to use two separate power transmitting crankshafts or at least one with a linkage system.

In the more recent past, free piston compressors have been developed in which each engine piston in an opposed free piston type engine is coupled directly to one compressor piston. This type of engine has important advantages over the above-described conventional arrangements in that it may operate as a two-cycle engine and yet the crankshaft with all its inherent disadvantages is eliminated. Such simple and compact free piston compressors have proven very efficient for delivering compressed air up to approximately 70 p.s.i.g. However, at higher delivery pressures and particularly at pressure where it becomes necessary to use two stages with intercooling, unbalances develop which makes it more difficult to effect the synchronism of the motion of the engine pistons. Various mechanisms, such as a rack and pinion arrangement, have been proposed, for synchronizing purposes, but it appears that a light crankshaft arrangement, which may also carry a flywheel for energy storage and may be used for starting purposes and to drive small auxiliary devices is the most practical one. The use of the light synchronizing crankshaft has posed some problems, however, and the main problem has been the means of connecting the engine pistons to the crankshaft without detracting from the otherwise advantageous features of the free-piston engine. In view of these problems, mechanisms have been devised using means such as crossheads rigidly connected to the piston rod of the engine piston and drivingly connected to the crankshaft.

It is an object of this invention to provide a relatively light and compact, semi-free piston compressor which is substantially free of the adverse features discussed above in connection with known devices.

According to the present invention there is provided in an engine-compressor type machine having a framework with a reciprocating engine piston reciprocably mounted in a combustion cylinder in the framework and with a compressor piston which is connected by a piston rod to the engine piston and is slidably disposed in a compressor cylinder which is aligned with the combustion cylinder, a crankshaft mounted in the framework for rotation about an axis extending perpendicular to the axis of the cylinders and a rocker beam pivotally connected to the framework for oscillation about an axis parallel to the axis of the crankshaft. Means are provided which pivotally joins the engine piston to the rocker beam at a point on the rocker beam spaced from the connection of the rocker beam to the framework, and a connecting rod, which is rotatably connected at one end to a throw of the crankshaft, is pivotally connected at the other end to the rocker beam at a point spaced from the connection between the rocker beam and the framework and the point of connection on the rocker beam of the means joining the rocker beam to the engine piston.

There is further provided in the present invention a pair of opposed engine pistons, a pair of compressor cylinders aligned one each at opposite ends of the combustion cylinders, a pair of compressor pistons disposed one each in the compressor cylinders and connected one each to one of the engine pistons by piston rods one each extending from opposite ends of the combustion cylinders, and a piston synchronizing mechanism. In this arrangement, the synchronizing mechanism includes a crankshaft having 180° spaced throws, and there is provided a pair of rocker beams with means pivotally joining one each to the engine pistons. A pair of connecting rods is provided one each having one end connected to one throw of the crankshaft with the other end thereof connected to one of the rocker beams. The crankshaft is provided with an auxiliary component drive means.

In the accompanying drawings, which show certain embodiments of the present invention, by way of example:

FIGURE 1 is a longitudinal sectional view in elevation of the compressor according to the present invention, certain parts being broken away for the sake of clarity;

FIGURE 2 is an enlarged transverse sectional view, the left part of which is taken along the line 2A__2A of FIGURE 1 and the right part of which is taken along the line 2B—2B of FIGURE 1;

FIGURE 3 is an enlarged sectional view of the piston rods connected to the engine piston as viewed from line 3—3 of FIGURE 1;

FIGURE 4 is an end view of the low pressure compressor unit at the right hand end of FIGURE 1;

FIGURE 5 is a view similar to FIGURE 3, but shows a cross-section through a further embodiment of the piston rods;

FIGURE 6 is a substantially horizontal sectional view through another embodiment of the crankshaft, connecting rod and rocker beam arrangement;

FIGURE 7 is a partial side view of a rocker beam according to the present invention and having a variable type connection to the framework;

FIGURE 8 is a partial side view of another embodiment of the rocker beam having a variable type connection between it and the connecting rod;

FIGURE 9 is a sectional view along the line 9—9 of FIGURE 8; and

FIGURE 10 is a sectional view along the line 10—10 of FIGURE 9.

3,369,733

In the drawings, the reference numeral 10 denotes generally the semi-free piston compressor of the present invention. With particular reference to FIGURE 1, it is to be noted that the compressor 10 consists in the main of a central engine portion 11 with two separate compressor 5 units 12 and 13 at opposite ends. The engine portion 11 includes a combustion cylinder 14 which is supported by an outer enclosure or casing 15, only parts of which are shown in the drawings, the casing 15 generally providing the framework of compressor 10. A pair of opposed en- χθ gine pistons 16, 16 is reciprocably disposed in the combustion cylinder, the pistons 16, 16 being directly connected by piston rods 19, 19 one each to compressor pistons 17 and 18 in compressor units 12 and 13, respec-. tively. The engine portion 11 further includes a synchro- 15 nizing mechanism 20 located closely under the combustion cylinder 14, in the form of a pair of rocker beams 21, 21 which are pivotally connected at their upper ends to the engine pistons by means such as piston rods 23, 23 and intermediate these ends to a light crankshaft 24 by 20 way of connecting rods 25, 25.

The combustion cylinder, which is normally horizontal as shown, may be in the form of any of several known types of water cooled diesel liners designed for a twocycle, opposed piston engine. As shown in FIGURE 1, 25 the combustion cylinder 14 is provided with surrounding coolant passages 26. A fuel injector 27, which is timed to squirt fuel into the combustion cylinder 14 between the pistons 16, 16, is situated midway of the combustion cylinder 14 in a well-known manner. Inlet ports 30 and ³⁰exhaust ports 31 are located in the walls of the combustion cylinder to permit scavenging in a known manner as the pistons 16, 16 approach the outer ends of their strokes and uncover the ports 30 and 31. The ports 30, which encircle the combustion cylinder 14 to the right of the injector 27, as viewed in FIGURE 1, are in direct communication on the outside, of course, with closed scavenging air reservoir 32 provided by casing 15. Exhaust ports 31, which encircle the combustion cylinder 14 to the left of the injector 27 as viewed in FIGURE 1, are ⁴⁰in communication with an exhaust duct 33 which leads to the outside of the compressor 10.

Each of the engine pistons 16, 16, which may in design be of any well known type of diesel piston, has a transverse, horizontal, gudgeon pin 34 mounted therein (see 45 FIGURES 1 to 3). The gudgeon pin 34 passes through the inner end of piston rod 19. Each of the piston rods 19 consists of an outer rod section 36 which is of circular cross-section and is rigidly connected at the outer end thereof to one of the compressor pistons 17 or 18. The 50 end of each rod section 36 opposite to the compressor piston is enlarged in the vertical direction and has opposite flat faces 37, 37 against which is clamped two parallel, elongated plates 38, 38 by a series of bolts 40, as best seen in FIGURE 3. The plates 38, 38 define a pair 55 of leg members of a bifurcated portion 41 of each piston rod 19. The ends of plates 38, 38 opposite to their connection to rod section 36 extend into the engine piston and form the portion of the piston rod 19 connected to the gudgeon pin as described above. The inner ends of the 60 plates 38, 38 in the engine piston have aligned gudgeon pin receiving openings (see FIGURE 2) and are joined by a sleeve member 42 which may be formed integrally therewith.

Each piston rod 23 is located between the legs of the 65 bifurcated portion 41 of one of the piston rods 19, i.e., between the pair of the plates 38, 38 and is substantially coextensive therewith, as best shown in FIGURES 1 and 3. The inner end of the piston rod 23 in the engine piston 16 is provided with an enlarged portion 43 encircling 70 sleeve 42 extending between plates 38, 38, the enlarged portion including a cap 44 secured to the connecting rod 23 by bolts 45, 45 for the sake of assembling the rod 23 on the sleeve 42. A bearing 46 is provided within enlarged portion 43 so that the piston rod is pivotally mounted on 75 sleeve 42, and is, in effect, therefore, pivotally mounted on the gudgeon pin 34 and can pivot relative to engine piston 16. The opposite or outer end of each piston rod 23 is also slightly enlarged and has a bore 47 parallel to the gudgeon pin 34. The bore 47 contains a bushing 50 and extending through bushing 50 is a pin 51 which is, as will be described in more detail below, carried by the rocker beam 21. Because of the geometry of system, each piston rod never assumes a steep angle with respect to the axis of the combustion chamber and departs only slightly from its 90° relationship with rocker beam 21.

The rocker beams 21, 21 which are of equal lengths, are pivotally connected at their lower end to the framework casing 15 substantially below the opposite ends of the combustion cylinder 14. The rocker beams are relatively long compared to the strokes of the pistons, and as best seen in FIGURE 2, each rocker beam 21 consists of a pair of substantially parallel lever members 52, 52. Each pair of lever members 52, 52 have at their lower ends aligned bores 53 which contain bushings 54. A pin 55, which is supported by a pair of lugs 56, 56 extending upwardly from the bottom of casing 15, passes through bushings 54 and thus pivotally mounted the rocker beam 21 about and axis parallel to the rotational axis of the crankshaft.

The upper ends of each pair of lever members 52, 52 straddle one pair of plates 38, 38 adjacent the connection of the bifurcated portion 41 of each piston rod 19 to the rod section 36. The pin 51 extends outwardly through aligned, enlarged openings 57, 57 in plates 38, 38. A boss 60 is formed at the upper end of each lever member (see FIGURE 3) which boss has a tapered bore 61 receiving a correspondingly tapered end portion 62 of pin 51, so that the pin 51 is carried between the bosses 60, 60 at the top of each rocker beam 21. Since piston rod 23 is journalled on pin 51, piston rod 23 is pivotally connected by pin 51 to the rocker beam 21.

At a point between pins 51 and 55, another pin 64, which is parallel to the two pins 51 and 55, is fixed between lever members 52, 52 of each rocker beam 21. Each connecting rod 25 has its one end extending between the lever members 52, 52 of one rocker beam 21, and this end is journalled on pin 64 via a bore 63 which receives a bushing 66 which in turn receives the pin 64. Thus, each connecting rod 25 is pivotally connected at one end to one of the rocker beams 21. The other end of each connecting rod rotatably encircles one throw 65 of the crankshaft 24, a bolted-on cap 69 being utilized in the connection between the connecting rod 25 and the throw of the crankshaft.

The crankshaft 24 need only be of light construction since it does not actually transmit any compressing force, and it is, of course, of a double-throw type, i.e., it has two throws of equal eccentricity spaced at substantially 180°. As shown in FIGURE 2, the crankshaft is mounted adjacent opposite ends in bushings 67 and 68 which are carried by casing 15, the axis of rotation of the crankshaft being perpendicular to the axis of the combustion cylinder 14. Also adjacent opposite ends of the crankshaft 24 two flywheels 70, 71 are fixed thereto. The flywheels 70 and 71 store part of the energy for returning the pistons 16, 16 to top dead center. However, not all of the return energy is transmitted to the flywheels through the rocker beam arrangement since some is stored in the air cushions of the compressor clearance volumes. In addition other bouncer chambers now well known in the free piston field may be used in combination with the flywheels. Also mounted on one end of the crankshaft 24 outside of the casing 15 is a sheave 72 which drives a belt 73. The belt 73 may be used to drive auxiliary devices such as a water pump, fan, and generator.

At least one of. the rocker beams 21 may carry an oil pump 75 as shown in the left hand rocker beam in FIGURE 1. As shown in this figure, walls 76 are provided around the pivot connection of the rocker beam to the

3,369, 5 casing so that a lubricant reservoir 78 is established at the lower end of the rocker beam. The pump 75 has a casing 79 defining a cylindrical pumping chamber 80. A pump piston 81 is slidably disposed in chamber 80 and has a piston rod 82 extending from one end of the 5 chamber. Rotatably mounted on the outer end of the piston rod 82 is a roller 83. The end of chamber 80 opposite to the end from which piston rod 82 extends is closed, and a coiled spring 84 compressed between the piston 81 and the closed end of the chamber biases roller 83 into engagement with the wall 76. Accordingly, as rocker beam 21 oscillates during operation of compressor 10, the piston 81 is reciprocated within chamber 80 due to the engagement of roller 83 with stationary wall 76. Adjacent the closed end of chamber 80, an inlet port 85 and an 15 outlet port 86 are provided. In communication with inlet port 85 is a duct 87 which provides a passage from a filter 88 located in reservoir 78 to inlet port 85. A ball check valve 89 is provided in duct 87 to permit flow only into chamber 80 from filter 88. Further ductwork, a part 20 of which is shown at 91 is provided for conducting oil under pressure from outlet port 86 to bushings 50 and 54 carried by the rocker beams and preferably to the bearings on the crankshaft 24. A ball check valve 92 is provided in duct 91 to prevent flow of the oil back into 25 chamber 80 during the outward stroke of piston 81.

As previously described, a compressor unit 12 is secured to the right hand end of the central engine portion 11, the compressor piston 17 being rigidly fixed to the outer end of piston rod 19. The compressor unit 12 is fixed to the 30 casing 15 by bolts 94 passing through annular flanges 95 and 96 and closes the right hand end of the casing 15. The compressor unit 12 may be connected by other means but it is important that it can be readily detached.

The compressor unit 12, which may be formed of com- 35 mercially available parts, is a low pressure unit and includes a compressor cylinder 101 in the form of a water cooled liner. The compressor cylinder 101 is axially aligned, of course, with the combustion cylinder 101. An end closure plate 102 is provided between compressor 40 cylinder 101 and the scavenging air reservoir 32, and at the opposite end of compressor cylinder 102 is closed by head 103. End closure plate 102 has a central opening 100 in which the portion 35 of piston rod 19 is slidably received. Sealing rings 109 are carried in opening 100 45 and engage piston rod 19. The head 103 is provided with a well-known type of intake valve 104 in the central portion thereof, the valve including a plurality of annular port covering sealing rings 105 which normally permit a flow of air to be sucked into compressor cylinder 101 50 through ports 106 as the piston 17 is drawn away from head 103 but close to prevent flow of air back through the valve 104 as the piston 17 returns through its compression stroke. The air drawn in through ports 106 is supplied from an air chamber 107 which is in turn sup- 55 plied by air from atmosphere drawn through an air cleaner 108 (see FIGURE 1). The air compressed ahead of compressor piston 17 as it is forced towards head 103 escapes through outlet delivery valve 110 which is similar to and surrounds intake valve 104. The valve 104 is 60 designed to permit flow of compressed air only from compressor cylinder 101 and into an annular air chest 111. The chest 111 communicates with a duct 112 for delivering the compressed air from low pressure compressor unit 12 to an intercooler 113 (FIGURE 4). The 65 intake valve 104 is provided with a commercially available unloading valve mechanism 114. The unloading valve mechanism 114 includes a diaphragm 115 which is exposed on one side by a line (not shown) to the delivery pressure of the compressor. The diaphragm 115 70 engages the spring loaded plunger 116, which in turn engages a reciprocably mounted cup member 117. The cup member 117 has a plurality of spaced legs 118 which extend through ports 106 and engage one of the rings 105. Thus when the delivery pressure reaches a predeter- 75

733 ⁶ mined value, the diaphragm 115 is forced inwardly to shift plunger 116 towards head 103, and the cup member 117 is thus pushed to hold the one ring unseated so that air escapes back into chamber 107 during the compressor stroke of piston 17.

As shown in FIGURE 1, the end closure plate 102 is provided with spring loaded, one-way disc-valves 120 which permit air which is compressed in compressor cylinder 101 between compressor piston 17 and end closure plate to pass from compression cylinder 101 and into scavenging air reservoir 32. As the compressor piston 17 moves outwardly from the end closure plate 102 cleaned air is drawn into the volume behind the compressor piston via four ducts 121 (FIGURE 4) which communicate with air chamber 107 and extend in an axial direction towards end closure plate 102. The ducts 121 communicate with ports 122 spaced equally about compressor cylinder 101. Each port 122 is situated on the opposite side of a flat air inlet space 123 as a wall 124 which is in the same plane as the end closure plate 102. Each air inlet space 123 communicates along one edge with compressor cylinder 101. Spring loaded, one-way disc valves 125 are provided in each port 122 to prevent flow of air back through ducts 121. The thickness of each space 123 is very thin in relation to its area in a radial plane. Since the air inlet spaces 123 are disposed radially outward from the compressor cylinder 101 the piston 17 can be pulled towards end closure plate 102 until it nearly engages the end closure plate, and due to this fact as well as the fact the spaces 123 are very thin, a small clearance volume exists for this portion of the compressor unit 12 which produces the scavenging air for the engine.

At the opposite end of engine portion 11 the compressor unit 13 is preferably connected to casing 15 by abutting flanges 130 and 131 and bolts 132 in a manner exactly the same as compressor unit 12. The compressor unit 13 is similar to compressor unit 12 but provides a high pressure stage which receives air from intercooler 113 through an air chamber 133 and delivers the highly compressed air to a delivery line (not shown) through an air chest 134. The compressor piston 18, which is of course smaller than piston 17 for the sake of balancing the power strokes of engine pistons 16, 16 is reciprocably mounted in a water cooled compressor cylinder 135. Compressor cylinder 135 has a head 136 substantially the same as head 103 and is equipped with an unload valve mechanism 137 the same as mechanism 114. The inner end of compressor cylinder 135 in this high pressure unit does not, however, include valving for providing scavenging air to scavenging air reservoir 32, but as in the case of the compressor unit 12 an end closure plate 140 is provided. The end plate 140 has a central opening 141 through which piston rod 19 extends and sealing rings 142 are provided to engage the piston rod.

In operation, the strokes of the engine pistons are timed and fixed in length, i.e., the pistons are phased, by crankshaft 24. However, this is achieved without developing any noticeable side thrusts on engine pistons 16, 16. Because the piston rods 23 are pivotally connected to the rocket beam 21 which is in turn pivoted to the framework, no couples are developed, and due to the small obliquity of the piston rod during the stroke because of the basic geometry of the linkage, the force transmitted to the rocker beam 21 is substantially along the central axis of the piston.

Due to the fact that piston rods 23 which oscillated slightly are completely separate from piston rods 19 which are connected to gudgeon pin 34 at one end and are rigidly fastened to pistons 17 and 18 at the other end, piston rods 19 move only through a straight reciprocating motion. Thus a very effective seal can be obtained by sealing rings 109 and sealing rings 142 which makes oilfree operation of the compressor units 12 and 13 possible.

Since the crankshaft 24 need only be of light construction, and is of a double throw type, its presence does not

3,369,733 develop any large unbalanced force. Moreover, since the low pressure compressor unit 12 and the high pressure compressor unit 13 are selected for substantial balanced operation the fact that the compressor 10 is a two-stage does not result in a large unbalanced force.

Referring now to FIGURE 5, it will be noted that the piston 16 and gudgeon pin 34 are again of standard design, but piston rods 19' and 23' are somewhat different from previously described piston rods 19 and 23. Moreover, the upper end of rocker beam 21', which is preferably a single member such as described in connection with the remaining figures, extends between elongated side members 38', 38 of the bifurcated portion 41' of piston rod 19'.

In the embodiment shown in FIGURE 5, rod section 36' of piston rod 19' may be cast integrally with side member 38', side member 38' being to one side of rod section 36' and connected thereto by an offset block section 150. The end of side member 38' within piston 16 has a sleeve portion 42' formed integrally therewith. The sleeve portion 42', which has its axis extending perpendicular to the longitudinal axis of the piston rod 19', has an outer cylindrical surface 151 surrounded by bushing 46'. The bushing 46' is journalled in a bore 153 in the inner end of piston rod 23' so that piston rod 23' is pivotally mounted on sleeve portion 42'. Sleeve portion 42' has an inner cylindrical surface 152 which is of greater diameter than the outer diameter of gudgeon pin 34.

The side member 38” is not formed as part of rod section 36' but is a separate member which has a sleeve portion 42 having an outer cylindrical surface 154 adapted to fit snugly within the inner cylindrical surface 152 of sleeve portion 42'. Sleeve portion 42 has an inner cylindrical surface 155 for tightly receiving gudgeon pin 34. The end of side member 38 opposite to that having sleeve member 42 is provided with openings 156 for receiving screws 157, the screws 157, one of which is shown in FIGURE 5, securing the side member 38 to the block section 150 so that side members 38', 38, sleeves 42', 42 and rod section 36' form a rigid unit.

As previously mentioned, the upper end of the rocker beam 21' extends between side members 38', 38, but it is bifurcated to provide spaced lugs 60', 60' having aligned bores 61', 61'. Bores 61', 61' receive pin 51' journalled in a bushing 50' in a bore 47' in the end of the piston rod 23' opposite to bore 153.

As may be readily observed, the piston rod 23' is of simpler construction than piston rod 23 in that it is not capped at the inner end, and yet the assembly of the arrangement shown in FIGURE 5 is simple. To assemble this preferred embodiment the one end of piston rod 23' is slid down over sleeve portion 42' while its other end is put between lugs 60', 60'. The pin 51' is then inserted to connect piston rod 23' to rocker beam 21' and side member 38 is then brought into place by inserting sleeve portion 42 into sleeve portion 42' and screwing in screws 156. Thus piston rod 19' is assembled with piston rod 23' journalled on sleeve portion 42'. After inserting the end of piston rod 19' in piston 16, with inner surface 155 of sleeve portion 42 aligned with the gudgeon openings in the piston. The gudgeon pin 34 is driven home to comnlete the assembly.

In the embodiment shown in FIGURE 6, it is to be noted that, unlike in the embodiment shown in FIGURES 1 and 2, the connecting rods 25', 25' and rocker beams 21', 21' are in a common plane and oscillate in the common plate. This arrangement is preferable in that it avoids the development of turning couples caused by out of line forces. The outer ends of the connecting rods 25', 25 are each bifurcated to provide lugs 160, 160 which straddle each rocker beam 21, each outer end being pivotally connected to the rocker beams by pins 64' carried by the rocker beam and passing through aligned bores 63', 63'.

The crankshaft 24' has actually three throws 65', 65 ⁸ and 65, but the two throws 65, 65 although axially spaced are on a common axis which is disposed 180° from the axis of throw 65'. Throw 65' is on the same common plane as rocker beams 21', 21' so that connect5 ing rod 25', which connects throw 65' to one rocker beam 21', consists of a simple straight member. The other connecting rod 25 is connected to both throws 65, 65 which in the axial direction of the crankshaft are spaced on opposite sides of throw 65', and accordingly, connecting rod 25 is forked to provide two leg portions 161, 161. The leg portions rotatably receive the pair of throws 65, 65 and straddle throw 65' as shown in FIGURE 6.

The rocker beams 21, 21 or 21’, 21' may be pivotally connected to the framework in a manner to permit the 15 variation of the axii of oscillation of the rocker beams as shown in FIGURE 7. In this alternative embodiment, instead of mounting the rocker beams on pins 55, each rocker beam 21' is mounted for oscillation on a circular bearing portion 165 so that the axis of oscillation of each 2o rocker beam is coincidental with the centre of the bearing portion 165. The circular bearing portion 165 is carried by a shaft 166 rotatably supported in lugs 56' and preferably extending to the outside of the compressor 10 so that it can be turned through at least 180° without 25 opening the compressor. The centre of circular bearing portion 165 is eccentrically disposed in relation to the axis of shaft 166 so that as shaft 165 is turned through an arc the centre of bearing portion 165, and thus the axis of oscillation of the rocker beam 21', is shifted relative to 30 the framework. In view of the fact the rocker beam is connected to the crankshaft by a rigid connecting rod, any displacement of the axis of oscillation of the rocker beam in a direction parallel to the axis of the combustion cylinder 14 automatically varies the positioning of the 35 pistons 16, 16 relative to each other, i.e., the travelled path of the piston in the cylinder is changed, and this in turn alters the compression ratio. As indicated above, it is preferable to make shaft 166 readily accessible so that the change can be carried out even when the machine is in 40 operation.

By changing the distance between the connection of the rocker beam to the framework of the compressor 10 and the pivotal connection of the connecting rod, it is possible, of course, to vary the length of the piston stroke. FIGURE 8 shows a rocker beam 21α which is somewhat 45 similar to rocker beam 21', rocker beam 21α being pivotally connected to the framework of the compressor by pin 55α. Connecting rod 25' connects the rocker beam 21α to the crankshaft 24' in the manner described above, but the actual connection between connecting rod 25' and 50 rocker beam 21α is adapted to shift the axis of pivot between the connecting rod and rocker beam towards and away from the axis of pin 55α. Journalled in rocker beam 21 is a shaft 178 which has a pair of eccentrically disposed, circular bearing portions 171, 171 formed on op55 posite ends thereof (see particularly FIGURE 9). Lugs 160, 160 are pivoted on bearing portions 171, 171, which shift relative to the axis of shaft 170, and thus relative to the axis of oscillation of the rocker beam, as shaft 170 is turned through an arc of up to 180°. Since the axis of 60 pivot between the connecting rod and the rocker beam is the common axis of bearing portions 171, 171, the turning of shaft 170 effects the oscillation of the rocker beam to vary the length of piston stroke. Means for turning the shaft 170 preferably from outside of the com65 pressor during operation is shown in FIGURE 9 and more particularly in FIGURE 10, and this means includes a semi-circular chamber 172 in rocker beam 21α at one side of shaft 170 and concentric therewith. A vane 173 is fixed to shaft 170 and extends radially therefrom, the 70 vane 173 having an outline conforming to the shape of the chamber 172 in a radial plane. Two passageways 174 and 175 are in communication with the chamber 172 on opposite sides of the vane 173 and lead through rocker beam 21α, pin 55a and the framework to control valves 75 (not shown).

3,369,733

Thus, by admitting pressurized fluid through one passageway, say passageway 175, for example, while permitting evacuation of the other, i.e. passageway 174, for example, the vane will be forced through an arc in the chamber 172, and as the vane is fixed to shaft 170, the 5 shaft will be rotated. As explained previously, this changes the location of the pivoted connection between the connecting rod and rocker beam and this in turn changes the piston stroke.

Moreover, with the designs described above, it is pos- jq sible to convert the compressor 10 from a two-stage compressor to a single stage compressor without destroying the balance by simply removing the compressor unit 13 and attaching a second low pressure compressor unit of the same construction as compressor unit 12. For exam- 15 pie, with an engine designed to develop 29 HP, the compressor of the present invention, when operating as a two-stage compressor with intercooling, can produce 90 c.f.m. at 150 p.s.i.g., and when converted to operate as a single stage compressor, can produce 110 c.f.m. at 105 20 p.s.i.g.

The two-stage compressor described above can also be twinned to increase the delivery, and this may be achieved by placing two units side by side and utilizing a common crankshaft. „5

These and other modifications obvious to those skilled in the art can be made to the embodiment described above and illustrated in the accompanying drawings without departing from the present invention, the scope of which is defined in the appending claims. ₃₀