US3588292A - Device for regulating,by reflux through the inlet-valve,the sucked flow for reciprocating compressors - Google Patents

Abstract

THE DELIVERY OF A COMPRESSOR IS CONTINUOUSLY AND PRECISELY CONTROLLED, EVEN DURING OPERATION, BY A MECHANICAL DRIVE REGULATING THE REFLUX THROUGH THE INLET VALVE, IN WHICH THE MOTION OF THE COMPRESSOR CRANK SHAFT IS TRANSMITTED BY MEANS OF HELICOIDALLY TOOTHED GEARS THROUGH AN INTERMEDIATE GEAR SHAFT TO A CAM SHAFT ON WHICH THERE IS KEYED A CAM WHICH DRIVES ADDITIONAL MECHANISM CONTROLLING THE FLOW THROUGH THE INLET VALVE TO THE COMPRESSION CYLINDER. THE RELATIVE POSITION OF THE DRIVING CAM AND THE CRANK SHAFT DIRECTLY DETERMINES THE DURATION OF THE REFLUX PERIOD, AND IS REGULATED BY AXIALLY SHIFTING THE INTERMEDIATE GEAR SHAFT. ADDITIONAL STAGES OF A MULTISTAGE COMPRESSOR MAY ALSO BE INDEPENDENTLY BY ADDING AN AXIALLY MOVABLE SHAFT AND A CAM SHAFT FOR EACH

ADDITONAL STAGE IN MESHING ENGAGEMENT WITH THE CAM SHAFT OF THE NEXT PREVIOUS GEAR TRAIN.

Description

limited Sttes tent FOREIGN PATENTS 9/1942 Germany.......i,.,i.,.....ii

[72] lnventor Costantino Vinciguerrn Firenze, lmiy 0115,11

[2]] Appl. No. [22] Filed Apr. 10, 1969 M5] Patented June 2%, W711 [73] Assignee Nuovo lPignoue SJPA.

ll-irenm,lltnly [32] Priority Nov. 15, 19M

lltuly {3H 82%75/68 ABSTRACT: The delivery of a compressor is continuously and precisely controlled, even during operation, by a 54 UIEVHQE mm REGULA'HNG' My REWJUX mechanical drive regulating the reflux through the inlet valve,

THWQUGH THE HNLETNALVETWE SUCMED in which the motion of the compressor crank shaft is transmitted by means of helicoidally toothed gears through an in- FILUW lFUlR REClIlPMOCATllNG COMlPllRlESSOlltS 5 tCluimsA Drawing Figs.

[52] US. Cl...

termediate gear shaft to a cam shaft on which there is keyed a cam which drives additional mechanism controlling the flow through the inlet valve to the compression cylinder. The relative position of the driving cam and the crank shaft directly MW mm M F [511 rm.ci.......llllllilIII:III, so Weldoiienrclli......

determines the duration of the reflux period, and is regulated by axially shifting the intermediate gear shaft. Additional stages of a multistage compressor may also be independently {56] References Cited UNITED STATES PATENTS ll/l953 Borel.............t.,.........m

controlled by adding an axially movable shaft and a cam shaft for each additional stage in meshing engagement with the cam shaft of the next previous gear train.

PATENTEnJuuzsmn 3,588,292

SHEET 3 BF 4 INYENTOR. CLMUMW z fiw 7?), [LLW PATENTED JUN28 I971 SHEET & UF 4 I NVE N TOR.

DEVICE FUR REGULATHNG, IBY hlElFlLUX THROUGH THE llNlLlET-VALVIE, TllllE SlUlCllflED FLOW lFOlR llilEClllPROCATlNG COMPRESSORS The present invention relates to a device for the continuous and controlled regulation of the flow of a reciprocating compressor cylinder by reflux through the inlet-valve of a part of the sucked flow, particularly suitable for high pressure reciprocating compressors.

As is presently known, after the compressor piston has reached its upper dead point (UDP) and after a further delay corresponding to an angular shifting or of the crankpin of the compressor mechanism, said shifting depending on the process of reexpansion of the gas remaining, at the feed pressure, in the cylinder noxious spaces, the inlet-valve opens and the gas is sucked into the cylinder during the period of time which elapses in order for the compressor piston to reach its lower dead point (LDP), i.e. for the time corresponding to an (l80) angular shifting of the compressor crankpin. As soon as the piston reaches its lower dead point (LDP) the inlet-valve closes under the action of its return spring and in the following period of time, corresponding to a 180 angular shifting of the crankpin, the gas is compressed and expelled from the cylinder through the feed valve.

In order to vary the amount of gas which is sucked into the compressor cylinder it is therefore necessary to operate in such a way that the compressor inlet-valve remains opened for a certain period of time after the piston has reached its lower dead point (LDP) so as to allow, in the compression phase, a reflux, through the same inlet-valve, ofa part of the gas previously sucked therethrough.

In the known art the delay in the closing of the inlet-valve, with a consequent variation ofthe gas flow to the compression cylinder, is achieved through an operating spring which exerts a force F on the inlet-valve shutter and keeps it opened by counteracting the closing action of the valve return spring. The closing of the valve occurs only when the reflux gas stream escaping into the inlet-duct through the opened valve may engender on the valve shutter a flow-dynamic force higher than the load F ofthe operating spring.

The regulation of the sucked flow is carried out by varying simply the same load F of the operating spring; in this way, in fact, the length ofthe gas reflux period is modified.

It has been found that the aforedescribed type of regulation presents remarkable difficulties and drawbacks deriving from the use ofa spring as generator ofthe operating force F.

Thus, it is difficult to calculate the forces exerted by the gas on the valve shutter in different closing conditions which results in a doubtful sizing of the spring and the impossibility of knowing, even because of variations and resonances of the spring itself, what is the flow reduction pertaining to a prefixed value of the force F. On the other hand, such a flow regulating device cannot practically be applied to high pressure reciprocating compressors, since the high loads involved would require the use of an operating spring having such large thickness and overall dimensions as to be impractical to build.

The object of the present invention is therefore the realization of a device for regulating the flow of reciprocating compressors which overcomes or eliminates the drawbacks of the prior art devices and which, by keeping opened the inletvalve during the reflux period by means ofa spring-free mechanical control, permits predetermined and continuous variation in the length ofthe reflux stage.

The invention is illustrated in detail with reference to the enclosed drawings showing a preferred embodiment given only by way of example, as many mechanical and structural variants may be thought without departing from the range of the invention.

FIG. 1 shows a flow regulating device which is representative of prior art constructions.

FIG. 2 shows the flow regulating device of reciprocating compressors constructed according to the invention.

FIG. 3 shows the circle described by the crankpin of the reciprocating compressor, on which the contour of the driving cam has been superposed in order to point out the angular relationships between the cam and crankshaft in the different phases of regulation.

FIG. t shows a system making use of two devices according to the invention for realizing an independent flow regulation in two successive phases of compression.

Referring initially to FIG. ll of the accompanying drawings, there is illustrated a flow regulating device which is representative of prior art constructions, in which the operating spring 1, which through the pushing element 2, imparts to the shutter of the inlet-valve 3 of the compressor Al, in opposition to the force of the return spring 5, the force F keeping the valve opened till the gas stream 6, escaping through the valve into the inlet duct 7, does not engender on the shutter 3 the flowdynamic force capable to exceed the load F of the operating spring 1.

It is possible to see the wheel 3 allowing to vary the value of the force F exerted by the operating spring l and therefore the gas reflux time and the flow sucked by the cylinder of the reciprocating compressor.

With reference to the FIG. 2 the regulating device according to the invention comprises a similar pushing element 2 which, urged forwardly in opposition to its associated return spring 9, acts on the shutter of the inlet-valve 3 of the compressor 4 and keeps said valve opened against the bias of inletvalve return spring 5.

In accordance with the invention, the advancement of the pushing element 2 is carried out by a driving cam llt) rotating in synchronism with the crankshaft 111 of the compressor 4 and acting on said pushing element through an hydraulic control. In detail, the cam it) acts with its contour on the wheel llZ hinged on the hydraulic cylinder 14 which, through the tube 15, controls the motion of the pushing element 2 according to the law required by the contour of the same cam 10.

Said driving cam 10 presents a contour such that its constant action angle i (see FIG. 3) is less than the angle l 01) corresponding to the opening of the inlet-valve in absence of regulation.

The action of the cam on the pushing element 2 through hydraulic control, as shown in H6. 2, represents only the most suitable and, consequently, the preferred form of transmission. It will be understood, however, that in particular cases, anyhow, the operation may be wholly automatic (carried out by rods and pivots).

The reflux time regulation and therefore finally the regulation of the sucked flow is carried out by suitably dephasing, during the compressor run, the angular position of the cam 10 as to the shaft ll of the compressor 4.

Referring now more particularly to FIG. 3, wherein T7 indicates the circle described by the crankpin 16, reference numeral 18 indicates the position occupied by said crankpin 16 when the compression piston is at its lower dead point (LDP) and accordingly the inlet-valve 3 closes because of its return spring 5, reference numeral 19 indicates the position of the pin corresponding to the upper dead point (UDlP) of the piston and reference numeral 20 indicates the position of the pin shifted a distance of 01 as to the position T9, in correspondence of which, as previously mentioned, there is an opening of the inlet-valve because of the depression engendered by the compressor piston.

Let us suppose the cam l0 initially has an angular position with respect to the shaft ll of the compressor 4 such that its contour is positioned as shown by uninterrupted line It) in the drawings.

In this case the inlet-valve 3 opens at the point 20 and after a further rotation B of the crankpin 116 the contour of the cam it) moves the pushing element 2 shifting it until its head is brought into touch with the shutter of the opened valve 3. The pushing element 2 keeps this position for 7 depending on the contour of the cam surface (in fact fi+y= l constant action angle of the cam) and thereafter the cam allows it to return into its initial rest position pushed therein by its return spring 9 and by the reflux gas pressure. Therefore, when the lower dead point (LDP) corresponding to the point 18 is reached, as

the pushing element 2 has retired, the return spring 5 may close the valve 3. l.e., in this case, the inlet-valve 3 is not affected by the motion of the pushing element 2 and the maximum quantity of sucked flow is therefore achieved.

Let us suppose now to dephase the angular position of the cam 8 in advance of the foregoing case, in which case the new position of cam contour with respect to the shaft 11 of the compressor 4 is shown in dashed line 10" in the drawing.

In this case the valve 3 is still open at the point and the approaching of the pushing element 2 to the valve shutter occurs after a different further rotation B of the crankpin 16.

The pushing element 2 and the valve 3 therefore do not interfere with each other.

At the lower dead point (LDP), however, corresponding to the point 18, when the inlet-valve 3 tends to close under the action of its return spring 5, said valve finds the pushing element 2 still shifted to its forward position by the contoured cam 10" and is therefore obliged to remain open.

The shutter of valve 3 therefore remains thrust against the pushing element 2 and is brought back into its seat only at the moment corresponding to the position 21 of the crankpin 16, depending on the contour of the cam 10.

The compression phase, rather than from the point 18, is therefore started from the point 21 because of the cam and it therefore results that the working piston stroke C is reduced to (C-Ac). Consequently the sucked flow into the compression cylinder is reduced proportionately to (C-Ac/c). It will be apparent from the foregoing that by dephasing the drive cam 10 by a predetermined angle with respect to the shaft 11 of the compressor 4 it is possible to vary the instant of closing of the inlet valve 3 and, accordingly, the reflux and, consequently, the sucked flow to the compression cylinder.

In accordance with the invention, means are provided for allowing the exact and continuous dephasing of a driving cam 10 with respect to the compressor shaft even while the compressor is in operation. To this end, referring particularly to FIG. 2, there is provided a housing 22 which is fixedly bolted on the side of the reciprocating compressor 4 opposite to the wheel and to which there is secured, by means of a suitable support, said cylinder 14 of the hydraulic control.

Inside housing 22 there are three parallel shafts supported by the front walls of the housing by means of sliding bearings. The shaft 23 is directly connected, through the flanges 24, to the crankshaft ll of the compressor 4 and on it a helicoidally toothed wheel 25 is keyed which engages a similar helicoidally toothed wheel 26 keyed on the second shaft 27. On this latter shaft there is also keyed another helicoidally toothed wheel 28, similar to the wheel 26 but with opposite spirals, which engages a similar helicoidally toothed wheel 29 keyed on the third wheel to which the driving cam 10 is keyed.

By means of the aforedescribed system the cam 10 turns in synchronism with the crankshaft 11 of the compressor 4. In fact an anticlockwise rotation of said crankshaft 11 and, accordingly, of the shaft 23 involves a similar rotation in opposite direction of the shaft 27 and therefore a rotation of the shaft 30 similar both in direction and in value to the one of the shaft 11. I

The two shafts 23 and 30 are further made fixed in the axial direction by means of suitable push-stands, whereas the shaft 27, with its toothed wheels 26 and 28 having opposite spirals, may be shifted axially, even during the compressor run, by means of an axial positioning element (not shown in the FIG.) which acts, manually or hydraulically, on the outside (left) end of the shaft 27. The dephasing of the cam I0 as to the crankshaft ll of the compressor 4 is carried out by axially shifting said shaft 27. Let us suppose, indeed, to prevent any rotation of the shaft 23 and to shift axially the shaft 27 of a length 5, e.g. in a direction opposite to the compressor. By this we engender a 6 rotation of the shaft 27 in a direction opposite to the one (supposed anticlockwise) of the crankshaft ll of the compressor, said rotation being engendered by the helicoidal coupling of the toothed wheels 25 and 26 transmitting the motion between the two shafts 23 and 27. A

similar rotation, but in an opposite direction, is carried out, of course, even by the shaft 30 engaging the shaft 27. Further the shifting s of the shaft 27 obliges the shaft 30 to turn further of 0, because of the helicoidal coupling between the wheels 28 and 29; summing up the shaft 30 turns of 20 in the usual direction of rotation of the crankshaft ll of the compressor 4.

From what said it results that by means of the axial shifting of the shaft 27 it is possible to dephase at will the cam 10 keyed on the shaft 30 as to the crankshaft 11 of the compressor 4 and, as the axial positioning elements (not shown) allows continuous and wholly controlled axial shiftings of the shaft 27, it is clear it is possible to obtain continuous and wholly controlled dephasings between the compressor shaft and the driving cam.

The illustrated device may even be used to simultaneously regulate the flow sucked by several cylinders of a single compressor. It is sufficient, for this purpose, to key on the shaft 30 as many driving cams as there are cylinders.

In the case of two compressing cylinders operated by opposite cranks, a single driving cam 10 is capable of regulating the flow by means of two similar hydraulic controls positioned on opposite sides of the cam.

It is clear that the flow reductions, obtainable by controlling the pushing elements of the inlet-valves of the different compressing cylinders with a single cam shaft 30, which equal in percentage.

For a two-phase compressor, by interposing between the cam shaft regulating the flow of the compressing cylinder of the first phase and the cam shaft regulating the flow of the compressing cylinders of the second phase a further dephasing device like the one above specified, it is possible to obtain different dephasings for the two cam shafts, i.e. to obtain different flow variations for the two phases and therefore to vary the pressure intermediate between the two phases of compression.

Thus, referring now more particularly to FIG. 4 of the accompanying drawings, there is shown a diagram for carrying out the aforedescribed differential dephasing for a compressor having a first phase cylinder and a second phase cylinder.

The cam 10, controlling the pushing element of the inletvalve of the compressing cylinder of the first phase of compression 4, is dephased with respect to the crankshaft ll of the two compressing cylinders, by axially shifting the shaft 27 of the dephasing device. The cam 10a, controlling the pushing element of the inlet valve of the compressing cylinder of the second phase of compression 4a, is on the contrary dephased as to the same crankshaft I1, independent of the dephasing of the first cam, by axially shifting the shaft 27a of a second dephasing device, like to the first one, which is operated by the helicoidal wheel 29 of the first dephasing device.

It will be seen in FIG. 4 that additional elements are indicated in connection with the second dephasing device by a reference numeral and the letter a, and it will be understood that, while not specifically referred to herein, these elements correspond to those elements already previously described having the same reference numeral applied thereto.

Iclaim:

1. In a device for regulating flow of compressors or the like by varying the period of reflux flow through the compressor inlet valve, including a pushing element operating against the closing action of the compressor inlet valve return spring and means for driving said pushing element, the improvement therein which comprises:

said means for driving said pushing element includes a cam member secured to a rotatable cam shaft, said cam member presenting a contour having a working arcual surface less than the arc described by the rotating crankpin of the compressor crankshaft, the latter corresponding to the normal opening time of compressor inlet valve; means for driving said cam shaft in synchronism with the crankshaft of said compressor, including: a helicoidally-toothed gear wheel secured to said cam shaft;

an intermediate rotatable shaft having secured thereto a pair of gear wheels having oppositely directed helicoidal teeth;

a further helicoidally-toothed gear wheel secured to a rotatable shaft driven by said compressor crankshaft;

one of said gear wheels secured to said intermediate shaft being in meshed, driving engagement with said cam shaft gear wheel and the other of said gear wheels secured to said intermediate shaft being in meshed, driven engagement with said further gear wheel driven by said crankshaft; and

means for axially moving said intermediate shaft with respect to said cam shaft and said shaft driven by said compressor crankshaft, said axial movement of said intermediate shaft varying the relative arcual position between said cam member and said compressor crankshaft and thereby also varying the period of said reflux flow through said compressor inlet valve.

2. A device as claimed in claim 1, wherein all of said helicoidally-toothed gear wheels have equal numbers of teeth.

3. A device as claimed in claim 1, wherein said gear wheels secured to said intermediate shaft are arranged so that said cam shaft is driven in the same direction of rotation as that of said compressor crankshaft.

4. A device as claimed in claim I, wherein said means for driving said pushing element includes a hydraulic system hav ing a piston member with cam member follower means secured thereto riding on the work surface of said cam member.

5. in a device for regulating the flow of a two-phase compressor by varying the period of reflux flow through the compressor inlet valve of each phase, including a pushing element operating against the closing action of the compressor inlet valve return pring of each phase and means for driving each of the pushing elements, the improvement therein which comprises:

each of the means for driving the first and second phase pushing elements includes:

a cam member secured to a rotatable cam shaft, said cam member presenting a contour having a working arcual surface less than the are described by the rotating crankpin of the compressor crankshaft, the latter corresponding to the normal opening time of the compressor inlet valves;

means for driving-the first phase cam shaft in synchronism with the crankshaft ofsaid compressor, including: a helicoidally-toothed gear wheel secured to said first phase cam shaft, a first intermediate rotatable shaft having secured thereto a pair of gear wheels having oppositely directed helicoidai teeth, and a further helicoidally-toothed gear wheel secured to a rotatable shaft driven by said compressor crankshaft, one of said gear wheels secured to said first intermediate shaft being meshed, driving engagement with said first phase cam shaft gear wheel and the other of said gear wheels secured to said first intermediate shaft being in meshed, driven engagement with said further gear wheel driven by said crankshaft; means for axially moving said first intermediate shaft with respect to said first phase cam shaft and said shaft driven by said compressor crankshaft, said axial movement of said first intermediate shaft varying the relative arcual position between the first phase cam member and said compressor crankshaft and thereby also varying the period of said reflux flow through said first phase compressor inlet valve; means for driving the second phase cam shaft in synchronism with said compressor crankshaft, including: a helicoidally-toothed gear wheel secured to said second phase cam shaft, and a second intermediate rotatable shaft having secured thereto a pair of gear wheels having oppositely directed helicoidal teeth, one of sald gear wheels secured to said second intermediate shaft being in meshed, driven engagement with said first phase cam shaft gear wheel and the other of said gear wheels secured to said second intermediate shaft being in meshed, driving engagement with said second phase cam shaft gear wheel; means for axially moving said second intermediate shaft with respect to said second phase cam shaft and said first phase cam shaft, said axial movement of said second intermediate shaft varying the relative arcual position between the second phase cam member and said compressor crankshaft and thereby also varying the period of said reflux flow through said second phase compressor inlet valve independently of said reflux flow through said first phase compressor inlet valve.

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