A compressor

Abstract: The invention relates to a reciprocating positive displacement compressor (1), of the type which includes at least two coaxial cylinders (2, 3), in which two relative pressers (22, 32) slide, powered by motor means through relative connecting and motion transmission means which include a connecting rod (6), connected in such a way that it can rotate at a first end or big end, to a crankshaft (8); in the compressor (1), the connecting and motion transmission means are positioned halfway between the pressers (22, 32), and have fixing means (25, 35), designed to contain and fix the connecting and motion transmission means, so as to create at least one double-action cylinder (X), whose compressing surfaces consist in the pressers (22, 32)

Description: The present invention is part of the technical sector which includes compressors, that is to say, machines designed to supply energy to a compressible fluid so as to provide a user machine with the same fluid at a greater pressure than that at which it was received. In particular, the present invention relates to a reciprocating positive displacement compressor. Double-action cylinders have a widespread application in the reciprocating compressor sector. In this type of compressor, both faces of the piston are active and the connecting rod which connects the compressor shaft to the piston is alternately moved by traction and compression, with different portions of the relative bearings in the two big ends which alternate in supporting the loads transmitted to the connecting rod. The solution currently used to transmit reciprocating motion to the piston of a double-action cylinder envisages the use of a rod, one end of said rod being engaged with the piston and the other end being fixed to a crosshead, which is in turn connected in such a way that it may rotate to the connecting rod. The presence of the shaft is disadvantageous to the form of one of the cylinder heads of the double-action cylinder, since, amongst other things, it makes it impossible to use a concentric suction/compression valve, which has the advantageous features described below. Thus, the advantages of concentric valves have traditionally been overlooked on at least one of the heads of the double-action cylinder, due to the above-mentioned structural constraints. Moreover, in double-action cylinders with a non-vertical axis, the above-mentioned technical solution implies the presence of mutual reactions between the piston and cylinder, reducing the life of the seal between the piston and cylinder liner. The above-mentioned advantages relative to the presence of concentric valves consist in containment of the clearance volume, the possibility of creating high sections of discharge, reducing pressure drops, as well as the possibility of giving the cylinder head an axial symmetrical shape, particularly suited to resisting pressure stress (this shape cannot be obtained in solutions which envisage valves positioned to the side of the cylinder axis). In document US-4 756 674 is disclosed a compressor with a crankcase which confines a pair of tie-rod-joined crossheads therein, and guides control reciprocation of the crossheads in horizontal and vertical planes. In this compressor the structure which supports the forces deriving from the gas on the pistons and the crankshaft comprises numerous elements and in particular the pistons themselves. From this arrangement results that the pistons are subjected to wear and therefore requires a relative large sliding surface and are relative heavy. In document US-4 729 291 is disclosed a compressor which has a pair of in-line cylinders, with pistons reciprocatable therein, and the crankshaft, having only one crank, is drivingly coupled to one of the pistons. The other piston is fastened to the crank-driven piston, in spaced-apart disposition, for a common reciprocation of the two. Also-in this compressor the forces deriving from the gas on the pistons and the crankshaft are supported from the pistons themselves, which should have a relative large sliding surface and are relative heavy. The present invention has for an object to provide a reciprocating positive displacement compressor with the crank system positioned halfway between the two compressing surfaces, set opposite one another, of the double-action piston. In this way, concentric valves may be used for each action. Moreover, since the two compressing surfaces of a piston slide within separate cylinders, they may have different transverse dimensions, making the compressor design more flexible. In the compressor disclosed by the present invention, the moving part of each crank system ends with the above-mentioned compressing surfaces. The said surfaces are obtained on two elements which, from a functional viewpoint, together form the double-action piston. Hereinafter, each of the said parts is referred to as a presser. The two pressers are engaged in an offset configuration, on the opposite side to the compressing surfaces, on two coaxial shafts, which are in turn connected to one another, in the example illustrated relative to a possible embodiment, by a ring-shaped element on which the small end of the connecting rod pivots. The ring-shaped element and the shafts (if necessary, with the aid of devices mentioned below) form the required prismatic connection between the piston and the base. In this way, on a compressor which does have concentric valves, a small drive mechanism is obtained, in which the double-action piston is prismatically linked to the base, to avoid incorrect interaction of the pressers and cylinder liners. In contrast to the known solutions, in the solution proposed by the present invention the piston activating device (crank system) is located halfway between the active faces of the piston (pressers), and the use of concentric valves allows a reduction of the clearance volume in the head, as well as simplification of the head shape, with the consequent advantages during construction of the compressor. The technical characteristics of the invention according to the above-mentioned objects are laid out in the claims below and the advantages of the disclosure are apparent from the detailed description which follows, with reference to the accompanying drawings, which illustrate a preferred embodiment of the invention and in which: Figures 1 and 2 are respectively a front view with some parts in cross-section and a partial side view with some parts in cross-section, of a possible embodiment of the present invention; Figure 3 is a front view with some parts cut away and others in cross-section, of a scaled up detail of the embodiment shown in the previous drawings. With reference to the accompanying drawings, a compressor of the type disclosed is of the positive displacement type and has one or more double-action pistons, each of which slides inside a pair of coaxial cylinders. In particular, in the embodiment illustrated without limiting the design concept, the compressor, labelled as a whole by the numeral 1, has four cylinders 2, 3, 4, 5 positioned in such a way that they form coaxial pairs and connected to one another (in serial and/or parallel fashion) so as to define a single/multi-stage compressor, according to the design specifications. The compressor 1 has a base 90 with suitable fixing means 9. In the accompanying drawings, the base 90 and fixing means 9, like the connections between the various stages and relative inter-coolers, are not described in detail since they are not part of the present invention. Reference shall now be made to the content of figure 2, that is to say, a piston X which slides in the cylinders 2, 3 (a piston Y, identical to piston X is envisaged for cylinders 4 and 5). Inside cylinders 2 and 3, pressers 22 and 32 are envisaged, driven with the aid of connecting rod 6 and suitable connecting and motion transmission means, by a crankshaft 8, to which a rotating connecting rod 6 is attached at the big end 61. The crankshaft 8 is connected to a motor by means of transmission parts 80, in a way substantially similar to that known to prior art. At the heads 21 and 31, the cylinders 2 and 3 have concentric valves 20, 30, directly opposite the pressers 22 and 32 of the piston X. The pressers 22 and 32, which slide inside the cylinders 2 and 3, are integral with respective shafts 23 and 33, which are in turn rigidly fixed to a ring-shaped element 7. The set of parts 22, 32, 23, 33 and 7 forms one double-action piston X. The portions of the piston X which come into contact with the base are the shafts 23 and 33 which slide within respective bushings 25 and 35 that are integral with the base 90. As already indicated, the present invention envisages that there are two surfaces integral with the base which are designed to axially guide the piston X, these being set at a relative distance from one another, so that halfway between them there is a pin 75 which connects the connecting rod 6 to the ring-shaped element 7. As shown in figure 2, a prismatic element Z with U-shaped cross-section is envisaged relative to piston Y of cylinders 4 and 5 (but also present for the piston of cylinders 2 and 3) both sides of which make contact with the ring-shaped element of piston Y, and although allowing the latter to slide, preventing it from rotating about its own axis, thus guaranteeing a correct contact in the connecting rod - piston and connecting rod - shaft rotary couplings. As is more clearly shown in figure 3, the ring-shaped element 7 has a gap 70 with width L7 not less than twice the value of the radius of the crank of the crankshaft 8, thus allowing the connecting rod 6 to oscillate freely within the ring-shaped element 7. Moreover, with reference to the non-limiting example illustrated, the shape of the gap 70 in the ring-shaped element 7 is substantially that of an isosceles triangle, with height not less than the total length of the connecting rod 6. The ends 24 and 34 of the shafts 23 and 33 are fixed to the opposite surfaces 72 and 73 of the ring-shaped element 7. The second end or small end 60 of the connecting rod 6 is linked in such a way that it may rotate, to the connecting ring-shaped element 7, close to one of the portions at which one of the shafts is attached (near portion 72 in figure 3). The connecting rod may be fixed to the ring-shaped element 7 as illustrated in the accompanying drawings: two plates 74 may be envisaged, designed to clamp the ring-shaped element 7 and simultaneously support the end of the pin 75, to which the big end 60 of the connecting rod 6 is linked in such a way that it may rotate. In this way, following the rotary movement of the crankshaft 8, the connecting rod 6 transmits a reciprocating straight motion to the piston X. Relative to a reference system integral with the said piston, the connecting rod 6 oscillates inside the gap 70. The second piston Y, more easily seen in figure 1, whose axis is at a right angle to that of piston X, slides inside cylinders 4 and 5, which have concentric valves 40 and 50, fixed to the respective cylinder heads 41 and 51. The pressers 42 and 52 are integral with the shafts 43 and 53, guided by the bushings 45 and 55. In conclusion, the present invention envisages that the crank system which transmits reciprocating straight motion to the double-action piston(s) of a compressor is physically positioned halfway between the means which link the piston(s) to the base. In other words, the crankshaft - connecting rod unit is confined to a space positioned halfway between the two guide bushings of a piston. The invention described can be subject to modifications and variations without thereby departing from the scope of the inventive concept

Claims: A reciprocating positive displacement compressor, of the type which includes at least two coaxial cylinders (2, 3), in which two relative pressers (22, 32) slide, said pressers being moved by motor means with the aid of connecting and motion transmission means including a connecting rod (6), its first end or big end (61) being connected in rotatable manner to a crankshaft (8), the compressor (1) wherein the said connecting and motion transmission means are positioned halfway between the pressers (22, 32), there being constraining means (25, 35) designed to contain and constrain the said connecting and motion transmission means, so as to define at least one double-action cylinder (X), the compressing surfaces of the latter consisting of the pressers (22, 32) characterised in that the connecting and motion transmission means include a ring-shaped connecting element (7), said element having a gap (70) the shape threof is substantially that of an isosceles triangle, with height substantially equal to but greater than the length of the connecting rod (6) and base substantially double the radius of the crank of the crankshaft (8). The compressor according to claim 1, characterised in that the cylinders (2, 3) have concentric valves (20, 30) on their heads (21, 31). The compressor according to claim 1, characterised in that the connecting and motion transmission means include at least two shafts (23, 33), these being respectively connected to the pressers (22, 32), these being axially connected and linked so that they are free to move axially. The compressor according to claim 3, characterised in that the connecting and motion transmission means include a ring-shaped connecting element, said element having a gap (70) whose width (L7) corresponds to double the radius of the crank of the crankshaft (8), that is to say, being designed to allow the connecting rod (6) to oscillate inside it; the ends of said shafts (23, 33) which are not fixed to the pressers (22, 32) being attached to the ring-shaped element (7) respectively at a first (72) and second (73) attachment portion, these being opposite one another; the second end or small end (60) of the connecting rod (6) being connected in such a way that it can rotate, to the ring-shaped element (7), close to one of the attachment portions of one of the shafts, so as to provide a reciprocating drive for the ring-shaped element (7) and shafts (23, 33) connected to it, with an oscillating movement of the big end (61) inside the gap (70). The compressor according to claim 4, characterised in that it envisages two plates (74), these being designed to clamp the ring-shaped element (7) at the portion of the element on which the connecting rod (6) pivots, and envisages a pin (75) which defines the connecting rod pivot at the small end. The compressor according to claim 3, characterised in that the constraining means include at least two bushings (25, 35), these being on the cylinders (2, 3) opposite the heads (21, 31) and being fitted over the shafts (23, 33) so as to constrain the latter in an axial direction. The compressor according to claims 2 and 3, characterised in that it also includes a third (4) and fourth (5) cylinder, these being opposite one another and coaxial, and having relative third and fourth pressers (42, 52), the latter being integral with the third and fourth shafts (43, 53), being contained and constrained in such a way that they can move axially, as well as motion transmission means (7'), these being envisaged between a second connecting rod (6') and the shafts (43, 53)., so as to define a second double-action cylinder (Y), the compressing surfaces being those of the third and fourth pressers (42, 52). The compressor according to claim 7, characterised in that the second double-action cylinder (Y) is substantially perpendicular to the first double-action cylinder (X). The compressor according to claim 7, characterised in that the third and fourth cylinders (4, 5) have concentric valves (40, 50) on the heads (41, 51).

Inventors: ZANARINI FRANCO, ZANARINI, FRANCO
Applicants: SAFE SRL, SAFE S.R.L.
Application year: 1997
Main classification: F04B27
IPC codes: F04B39, F04B27, F04B25