EP0775826A1 - Screw compressor - Google Patents

Abstract

The helical compressor has a compressor housing with an inlet (50) and an outlet for the medium which is to be compressed. It has two helical elements which are arranged in a chamber in the housing, and which extend between the inlet and the outlet. The elements engage in one another, in order to form closed compression spaces. Openings (70) for controlling performance are arranged in a chamber wall region which bounds compression spaces which are closed at maximum performance. Each opening is arranged at a place which corresponds to a different compression ratio, and one of several control elements can either fill in the opening in order to close it, or can stand at a distance from the opening, in order to connect it to a channel (72) which is joined to the inlet.

Description

The invention relates to a screw compressor for gas circuits, in particular for refrigeration systems, comprising a compressor housing with an inlet and an outlet for the medium to be compressed, two screw bodies arranged in a screw chamber of the compressor housing and extending between the inlet and the outlet, which form between closed compression spaces located at the inlet and outlet.

Screw compressors of this type belong to the displacement machines with a permanently installed compression ratio. In the case of such displacement machines, the sucked-in volume is reduced to a structurally predetermined final volume by reducing the compression spaces. The result of this is that, at system pressures that deviate from this fixedly specified or built-in pressure ratio, over or under compression can take place with a correspondingly reduced efficiency. If liquids are sucked in, even strong hydraulic pressure peaks, so-called "liquid hammer", can occur.

Power regulation of such screw compressors via a so-called volume slide is known from VDI reports No. 1135, 1994. Such a volume slide achieves a continuous adjustment to different load conditions, with such a volume slide built-in pressure ratio of the compressor as well as the volume ultimately sucked in at partial load can be corrected.

However, such a volume slide has the disadvantage that the construction effort is very high, since the volume slide has to be guided in a groove near the border to the screw chamber and thus additional tolerances arise between the slide and the screw bodies.

The invention is therefore based on the object of improving a screw compressor of the generic type in such a way that it permits the most advantageous power control possible.

This object is achieved according to the invention in a screw compressor of the type described in the introduction in that in a wall region of the screw chamber which delimits closed compression spaces at maximum capacity, there are provided a plurality of power control openings, each corresponding to different compression ratios of this wall region, each of which has either one of a plurality of separately operable control bodies can be closed in that the control body essentially fills the power control opening, or can be connected to a return flow channel connected to the inlet in that the control body is at a distance from the power control opening.

The advantage of the solution according to the invention can be seen in the fact that the control body, which can be moved into the power control opening and essentially fills it, on the one hand gives the possibility of the Closing the power control opening and, on the other hand, the possibility is created of connecting the individual power control openings in the desired number to the return flow channel by separately actuating the individual control bodies, so that a power control similar to the volume slide can be reached on the inlet side, but on the other hand this power control can be integrated into the compressor housing in a more advantageous manner leaves and also with closed power control openings, the dead space - if such should exist - is minimal.

It is particularly expedient if the control bodies can be moved transversely to a cross-sectional area of the respective power control opening in the direction away from the screw chamber, so that the axial movement of parts adjacent to the screw chamber known from the prior art, which poses the known design problems, can be avoided.

In order to minimize the dead space possibly still formed in the power control openings closed by the control bodies or to let them go as far as possible towards zero, it is advantageously provided that the control bodies have an end face with which the respective power control opening in the closed position of the control bodies of the wall surface of the Screw chamber can be appropriately closed in this area, so that in the area of the closed power control openings there is neither a dead space nor a leak when passing through the screw comb.

In principle, it is conceivable within the scope of the solution according to the invention to assign the plurality of power control openings to only one screw body of a screw compressor and thus to achieve power control, but this would lead to the compression spaces which form between the other screw body and the wall of the screw chamber being difficult to relax . For this reason, it is much more expedient for power control if a plurality of power control openings is assigned to each screw body, so that power control can be carried out by means of the compression spaces formed in each screw body.

In principle, the power control openings can be distributed over the wall areas delimiting the compression spaces. For reasons of the simplest possible actuation of the control bodies, it is particularly expedient if the power control openings are arranged along a line lying in the wall surface of the screw chamber, the line being a screw line, a circular line or a straight line.

In order to enlarge the flow cross-section of the individual power control openings, it is also conceivable to provide several lines of power control openings running side by side.

It is particularly advantageous if the power control openings are arranged in a row parallel to the axial direction, since in this case the control of the individual control bodies can be implemented in a particularly expedient manner. At Such an arrangement then corresponds to different locations on the line defining the row at different distances from the inlet side.

For manufacturing reasons, it is particularly advantageous if all control bodies are of identical design, so that the corresponding power control openings are also of identical design, and thus the plurality of power control openings can be produced particularly expediently and inexpensively with the control bodies closing them.

The power control openings are preferably arranged along the line in such a way that adjacent power control openings are at substantially the same distance from one another.

In order to achieve particularly efficient power control, it is advantageously provided that the center-to-center spacing of successive power control openings is less than twice the distance between successive screw combs.

The distance between the power control openings is preferably less than twice the extent of the power control openings in the axial direction, more preferably a maximum of 1.8 times or a maximum of approximately 1.5 times this extent.

Furthermore, it is advantageously provided that the power control openings extend in the direction of the line over at least the width of a screw comb of the screw bodies in the region of the wall surface of the screw chamber.

This extension preferably corresponds approximately to the diameter of a power control opening with an approximately round contour.

The maximum extension of the power control openings in the direction of the line or the maximum diameter is preferably approximately 1.5 times the distance between two successive screw combs, more preferably approximately the distance between two successive screw combs.

The number of power control openings is in particular at least two, preferably at least three, in order to be able to implement a sufficiently fine-level power control.

The maximum number of power control openings is preferably seven, but in many applications also five.

The number of power control openings and their size is preferably selected so that essentially stepless control of the power is possible.

The control of the individual control bodies can take place in the most varied of ways. For example, it would be conceivable to actuate the control bodies by means of a drive element which successively detects or releases a plurality of control bodies.

However, it is particularly advantageous if a drive element is assigned to each control body.

A particularly expedient exemplary embodiment of the solution according to the invention provides that the drive element for closing the power control opening is acted upon by the control body with a force proportional to the pressure on the outlet side. This type of design of the drive element has the advantage that the force provided for closing the power control opening is dependent on the pressure on the outlet side and can therefore be selected such that a pressure peak which forms in a compression space can be compensated for, for example by the suction of liquid that the control body of this pressure spike is evasively moved briefly out of its position closing the power control opening, but after the pressure spike is reduced, the force acting on the control body through the drive element immediately causes the power control opening to close again.

With this solution, in addition to the advantageous type of power control already described above, the possibility is created to use the control bodies serving for power control at the same time in order to reduce undesirable pressure peaks in the compression spaces, for example due to the suction of liquid, and thus, in addition to power control, hydraulic overload protection to have available.

The force acting on the control body in its position closing the power control opening is preferably slightly greater than the local force acting on the control body, which would occur in the screw chamber at outlet pressure.

The drive element could, for example, be actuated electrically.

However, a pressure medium-actuated drive element is particularly advantageous, since it means that there is no need to install an electrical supply.

In order to be able to actuate the drive element advantageously, it is provided that it can be actuated for transferring and / or holding the control body in its position closing the power control opening with a medium under a control pressure proportional to the outlet-side pressure, so that the pressure generated by the screw compressor is used for Generation of the force acting on the control body can be used.

In the case of a drive element actuated by a pressurized medium, it is also advantageous if the control element, in the position of the control body which connects the respective power control opening to the return flow channel, can be acted upon with a control pressure which is proportional to the inlet-side pressure.

In the simplest case, the design of the pressure medium-actuated drive elements provides that each drive element has a control piston, on which the local pressure in the screw chamber at the location of the respective power control opening and the control pressure act. This embodiment makes it particularly advantageous to ensure that the control body responds to the undesired pressure peaks in the manner described.

In principle, there would be the possibility of providing the control body separately from the piston.

In a structurally particularly simple solution it is provided that each control body is part of the respective control piston of the drive element.

For manufacturing reasons, it is particularly advantageous if control pistons are used if all control pistons are of identical design.

In order to achieve a suitable guidance of the control pistons in the compressor housing, the control pistons are expediently arranged in bores in the compressor housing which run transversely to the axial direction of the screw bodies, and are guided in these, whereby in the case of integration of the control bodies in the control piston, this also ensures that the control body is guided .

For manufacturing reasons, it is particularly expedient if the bores run parallel to one another with their axes.

The bores can be produced even more advantageously if the axes of the bores lie in one plane, so that the multiplicity of bores can be made in a single production step.

The control pistons are advantageously designed such that their side facing away from the control body has a piston surface which can be acted upon by the control pressure and delimits a control cylinder chamber.

To control the individual drive elements and thus also the individual control bodies, a power control device is advantageously provided, with which it can be determined which power control openings are to be closed or connected to the return flow channel.

Power control would already be possible by opening the power control opening, the compression ratio of which is closest below the selected compression ratio, from which compression should take place to the outlet. In this case, the medium would be compressed from the inlet to the compression ratio corresponding to the open power control opening and then flow back through the power control opening and the return flow channel to the inlet.

However, it is particularly advantageous if the power control device opens all the compression ratios corresponding to the power control openings corresponding to the selected compression ratio, since then essentially no compression takes place up to the selected compression ratio and the shaft power required to drive the screw compressor can thus be reduced approximately in proportion to the cooling or useful power of the screw compressor .

In order to be able to individually control and apply control pressure to individual control cylinder chambers in a suitable manner, it is advantageously provided that the control cylinder chambers of different control bodies are connected to different outputs of a power control device which specifies the control pressures at the outputs.

The power control device could basically be designed so that it comprises a valve block with a plurality of valves. However, it is structurally far simpler if the power control device has a movable control slide, through which selected outputs of the power control device can be acted upon with different control pressures.

A constructively expedient solution provides that the control slide is arranged in a control channel and the control slide divides the control channel into a section in which the pressure proportional to the outlet-side pressure is present as a control pressure, and another section in which a maximum of there is proportional pressure as the control pressure, and that the individual control cylinder chambers are connected to this via branch lines branching off at different points in the control channel, so that, depending on the section of the control channel into which the branch lines open, the respective control pressure is present in the control cylinder chambers.

The control channel is preferably oriented such that it extends in the axial direction of the screw body in the compressor housing and the control slide can also be displaced in the axial direction in the latter.

A particularly advantageous development of this solution with the control channel provides that a non-return valve blocking a gas flow from the inlet into the inlet-side section is arranged between the inlet-side section of the control channel and the inlet. Such a check valve makes it possible in the inlet-side section of the Generate control channel a pressure that is still below the inlet-side pressure, so that - for example when starting the compressor - to bring all the control pistons into their positions that release the power control openings, which is possible, for example, by moving the control spool while enlarging the inlet-side section of the control channel.

An advantageous further development of the solution according to the invention provides that the control bodies are provided with an injection opening for injecting a medium into one of the compression spaces which are formed, and that the injection opening of a control body closing the respective power control opening can be connected to an injection channel, so that the control bodies are used for this purpose can, in their position closing the power control opening, also serve to inject a medium into one of the compression spaces which are formed.

This solution according to the invention has the great advantage that it opens up the possibility of providing a possibility for injecting a medium into an enclosed compression space despite a power control of the screw compressor, without the case that - for example at very low power of the Screw compressor - the medium is injected before closed compression spaces are formed.

A particularly advantageous solution provides that the injection opening of the position closest to the selected compression ratio with its compression ratio and in its position closing the power control opening standing control body is connected to the injection channel. This ensures on the one hand that the injection of the medium does not take place before the formation of closed compression spaces and on the other hand ensures that injection of the medium is possible via the control body in the closed compression spaces which have just been formed.

In order to ensure in a simple manner that a connection between the injection channel and the injection opening is only possible when the control body is in its position closing the power control opening, it is advantageously provided that the connection between the injection opening and the injection channel is relative by the position of the control body is controllable to the power tax opening. The simplicity of this solution is of great advantage.

In order to further ensure that the control body closest to the selected compression ratio and closing the power control opening with its compression ratio has an injection opening connected to the injection channel, it is preferably provided that each control body in its position connecting the power control opening with the inlet corresponds to the next control body corresponding to a higher compression ratio connects to the injection channel. All of the control bodies which do not close the respective power control opening thus serve to establish a connection between the control body which comes closest to the selected compression ratio with its compression ratio and closes the power control opening and the injection channel.

In order to further ensure that only the injection opening of the control body closest to the selected compression ratio with its compression ratio is connected to the injection channel and not the control body corresponding to the injection openings of the further higher compression ratios, it is advantageously provided that each control body in its position closing the power control opening connects the Injection opening of the next control body corresponding to a higher compression ratio interrupts with the injection channel.

As an alternative or in addition to the previously described exemplary embodiments according to the invention, comprising power control openings which can be closed with control bodies, another example of a solution according to the invention provides that an overcompression control opening is provided in a wall area of the screw chamber which delimits compression spaces and which has a control body in a first position thereof with a control body can be closed and a second position of the same can be connected to the outlet, the control body being elastically acted upon by a force proportional to the pressure on the outlet side.

This solution according to the invention has the great advantage that it offers the possibility of designing the screw compressor in such a way that the desired maximum compression ratio can be achieved, but then the screw compressor can still be operated with a lower compression ratio without over-compression occurring, namely in that the control body in this case opens the over-compression control opening and connects it to the outlet, so that the medium having the desired maximum compression can flow to the outlet.

In this solution according to the invention, the possibility of reducing the compression ratio to such an extent that the maximum compression takes place only approximately at the pressure desired in the outlet is already created merely by changing the pressure in the outlet.

In order to avoid over-compression in the compression spaces formed by both screw bodies near the outlet, it is advantageously provided that at least one over-compression control opening is assigned to each screw body.

In principle, the over-compression control opening can either be arranged on the end face of the screw body in the region of the outlet-side end face of the compressor housing or also on the casing side of the screw body also in the region of the compressor housing near the outlet.

In the latter case in particular, there is the possibility of advantageously providing a plurality of over-compression control openings located in front of the outlet at different compression ratios.

The control body closing the overcompression control openings is expediently designed in such a way that, in its first position, it essentially fills the overcompression control opening in order not to create any dead spaces in this first position either inside the compressor housing, that is to say in the region of the screw chamber.

The regulating body is preferably designed such that it has an end face with which the respective overcompression regulating opening in the first position thereof can be closed with a surface corresponding to the wall surface of the screw chamber in this area.

In many cases it is sufficient to arrange one over-compression control opening per screw body. However, it is particularly advantageous if a plurality of overcompression control openings are provided, the plurality of overcompression control openings preferably being arranged either on the end face or on the casing side of the screw body.

With regard to the mobility of the control body relative to the over-compression control opening, no further details have been given in connection with the previous explanation of the individual exemplary embodiments.

For example, an advantageous exemplary embodiment provides that the control body can be moved transversely to the end face of the over-compression control opening.

For reasons of manufacturing technology, it is particularly expedient if all the regulating bodies are of identical design.

The regulating body is preferably part of a regulating piston, on which, on the one hand, the local pressure in the screw chamber acts at the location of the over-compression regulating opening and, on the other hand, the force proportional to the pressure on the outlet side.

In the simplest case, the force proportional to the outlet-side pressure can be obtained in that the control piston has on its side opposite the control body a piston surface which is acted upon by a pressure which is proportional to the outlet-side pressure.

When using control pistons, it has proven to be inexpensive for the sake of the simplest and most convenient production if all control pistons are of identical design.

The control piston itself can be arranged in a wide variety of ways. An advantageous embodiment provides that the control piston is arranged in a piston bore in the compressor housing.

This bore can either run parallel or transversely to the axial direction of the screw body, wherein in the case of several control pistons arranged on the casing side of the screw body, the bores are preferably aligned transversely to the axial direction of the screw body.

With a view to particularly cost-effective production, the piston bores are preferably arranged with their axes running parallel to one another.

It is particularly expedient if the axes of the piston bores lie in one plane. A particularly favorable solution with regard to advantageous production provides that the control pistons and the control pistons are of identical design, so that they can be manufactured identically and the corresponding bores for receiving the same can also be manufactured identically.

This production of the individual bores can be carried out particularly advantageously if the axes of the piston bores and the bores lie in one plane, so that these can be used, for example, with several tools in one operation or with one and the same tool in successive but in each case in the same plane operations can be produced.

Further features and advantages of the solution according to the invention are the subject of the following description and the drawing of some exemplary embodiments.

Fig. 1

einen schematischen Längsschnitt durch einen erfindungsgemäßen Schraubenverdichter;

Fig. 2

einen Schnitt längs Linie 2-2 in Fig. 1;

Fig. 3

einen teilweisen Längsschnitt längs Linie 3-3 in Fig. 1;

Fig. 4

einen Schnitt ähnlich Fig. 3 durch eine Variante des Ausführungsbeispiels gemäß Fig. 3;

Fig. 5

einen vergrößerten Schnitt längs Linie 5-5 in Fig. 3;

Fig. 6

einen Schnitt ähnlich Fig. 5 durch eine zweite Variante.

The drawing shows:

Fig. 1

a schematic longitudinal section through a screw compressor according to the invention;

Fig. 2

a section along line 2-2 in Fig. 1;

Fig. 3

a partial longitudinal section along line 3-3 in Fig. 1;

Fig. 4

a section similar to Figure 3 through a variant of the embodiment of FIG. 3.

Fig. 5

an enlarged section along line 5-5 in Fig. 3;

Fig. 6

a section similar to FIG. 5 through a second variant.

An embodiment of a screw compressor according to the invention, shown in FIG. 1, comprises a compressor housing, designated as a whole by 10, with a screw chamber 12, in which two screw bodies 14 and 16 are rotatably mounted. The two screw bodies 14 and 16 are part of rotors designated as a whole with 18 and 20, which in addition to the screw bodies 14 and 16 also comprise shaft ends 22 and 24 or 26 and 28 with which the rotors 18 and 20 on both sides of the screw chamber 12 are rotatably supported in the housing 10. The stub shaft 22 of the rotor 18 representing a main rotor is led out of the housing 10 and can be driven by a drive at its end facing away from the screw body 14.

As shown in Fig. 2, the screw bodies 14 and 16 are each rotatably arranged about mutually parallel axes 30 and 32 in the screw chamber 12 such that an outer contour 34 or 36 of a screw comb 15 or 17 of each screw body 14, 16 sealing abuts a wall surface 38 of the screw chamber 12. Furthermore, the screw combs 15 and 17 of the screw bodies 14 and 16 additionally intermesh, so that between the screw combs 15, 17 and the wall surface 38 of the screw chamber 12 in development, V-shaped compression spaces 40 and 42 are formed, the volume of which rotates the screw body 14 and 16 is reduced in size about the axes 30 and 32, respectively, so that the medium enclosed in these is compressed in these compression spaces 40 and 42, respectively.

The medium to be compressed is, as shown in FIG. 1, supplied via an inlet 50 and, as shown in FIGS. 3 and 4, exits through an outlet 52, the outlet 52 has an outlet opening 54 which opens into the screw chamber 12 and which is arranged on the end face of the screw chamber 12 in a plane perpendicular to the respective axis 30 or 32, while the inlet 50 comprises a recess 56 which azimuthally surrounds the screw bodies 14 and 16 on the inlet side.

As shown in FIG. 2, the recess 56 of the inlet 50 extends over approximately the upper half of the screw bodies 14 and 16, so that after a screw comb 60 or 62 runs past an inlet edge 64 defined by a lower end of the recess 56 between the screw combs 15 and 17 the closed compression spaces 40 and 42 are formed.

In a wall area 66 of the screw chamber 12 delimiting the closed compression spaces 40 and 42, as shown in FIGS. 3 and 4, several successive power control openings 70a to 70h are provided in the axial direction 68 from an inlet side, which together form a row in the illustrated case and in follow approximately equal intervals A.

Preferably, all of the power control openings 70a to 70h have the same shape and cross-sectional area.

As shown in FIG. 5, each of these power control openings 70 opens into the screw chamber 12, wherein a compression ratio can be assigned to each of the power control openings 70a to 70h in that a compression space 40, 42 above this always has the medium to be compressed with the same compression ratio . The greater the distance between the respective power control openings 70 in the axial direction 30, 32 from the inlet side, the greater the compression ratio assigned to this power control opening, since the volume of the compression spaces 40, 42 above it becomes smaller and smaller.

Opposite the screw chamber 12, each of the power control openings 70a to 70h opens into a return flow channel 72 which is connected to the inlet 50 and which, for example, also extends in the axial direction 68 from the inlet 50.

Furthermore, in continuation of each power control opening 70 in the housing 10, a piston bore 76 is provided which extends into a housing body 74, which directly adjoins the power control opening 70, penetrates the return flow channel 72 and then penetrates even further into the housing body 74 up to a bottom surface 78 A branch channel 80 opens into the bottom surface 58 and represents an output of a control channel designated as a whole by 82. The control channel 82 is, as shown in FIGS. 3 and 4, connected to the outlet 52.

Arranged in the piston bore 76 is a control piston, designated as a whole by 84, which comprises a piston surface 86 facing the bottom surface 78 and opposite it a control body 88, which in turn can be inserted sealingly into the respective power control opening 70 and with it, one of the screw chamber 12 facing end face 90 of the control body 88 is adapted in shape to the shape of the wall surface 38 in the wall region 66, so that the power control opening 70 seals through one final control body 88 in the area of the power control opening 70 with respect to the screw chamber 12, a zero-volume volume of the remaining space remains.

The power control opening 70 is preferably designed as a bore with cylindrical wall surfaces 92, which are arranged coaxially to a cylinder axis 94 of the piston bore 76, but have a smaller radius than the piston bore 76, so that an annular flange is located on the side of the power control opening 70 opposite the screw chamber 12 96 forms against which the control piston 84 in its position, which closes the power control opening 70 with the control body 88, can in turn be placed with an annular surface 98. The control body 88 preferably rises above the annular surface 98 with cylindrical surfaces 100, so that the control body 88 with its cylindrical surfaces 100 can be inserted appropriately into the cylindrical wall surfaces 92 of the power control opening 70 and exactly through the annular flange 96 and the annular surface 98 with its end face 90 Height of the wall surface 38 can be positioned in the area of the power control opening 70.

The piston surface 86 in turn delimits, together with the region of the piston bore 76 between this and the bottom surface 78, a control cylinder chamber 110 which is connected to the control channel 82 via the branch channel 80.

If the respective control cylinder chamber 110 of the corresponding control piston 84 is acted upon by a control pressure corresponding to the pressure in the outlet 52, the control piston 84 moves away from the bottom surface 78 and closes the respective power control opening 70 with the control body 88, so that there is no connection between the pressure spaces 40 or 42 formed above the respective power control opening and the return flow channel 72 connected to the inlet 50 via this power control opening 70.

However, the control piston 84 also has a control function, in particular an overload protection function, because when an overpressure occurs - for example due to the suction of liquid - in the compression space 40 or 42 above the respective power control opening, this overpressure acting on the end face leads to a force which leads to the force Exceeds force generated by the outlet pressure when it acts on the piston surface 86.

The control piston 84 thus moves in the direction of the bottom surface 78 until the control body 88 clears the power control opening 70 and the excess pressure can be reduced via the return flow channel 72. The force generated by the pressure on the outlet side and acting on the piston surface 86 is then greater again, so that the control body 88 closes the power control opening 70 again.

If the control pressure in the respective control cylinder chamber 110 corresponds approximately to or is less than the inlet-side pressure, the pressure acting on the control piston 84 in the region of the end face 90 of the control body 88 and the annular surface 98 in the respective compressor chamber 40, 42 leads to the fact that the control piston 84 moves in the direction of the bottom surface 78 until the piston surface 86 on the Floor surface 78 rests. In this case, the control body 88 opens the respective power control opening 70, so that the compressor space 40 or 42 located above this power control opening 70 is connected through the power control opening 70 to the return flow channel 72 which is connected to the inlet 50. In the return flow channel 72, a pressure is formed by the medium flowing back to the inlet 50, which is slightly above the inlet-side pressure and sufficient to move the control pistons 84 against the action of a control pressure corresponding to the inlet-side pressure on the piston surface 86 in the position which releases the power control opening to keep.

Control of the respective control pistons 84 is possible in that the branch channels 80a to 80h leading to the different piston bores 76a to h are arranged at different axial distances from an inlet-side end 112 of the control channel 82. Furthermore, the inlet-side end 112 of the control channel 82 is connected to the inlet 50 via a connecting channel 114, while an outlet-side end 116 is connected to the outlet 52 via a connecting channel 118. By means of a slide 120 provided in the control channel 82, the control channel 82 can be divided into an inlet-side section 122 and an outlet-side 124, a pressure corresponding to the pressure in the outlet 52 being present in the outlet-side section 124 due to the connecting channel 118, while in the inlet-side section 122 due to the connecting channel 114 there is a pressure which corresponds to the pressure in the inlet 50.

Depending on whether the branch channels 80 open into the inlet-side section 122 or the outlet-side section 124, the control pistons 84 are subjected to a control pressure corresponding to the inlet-side pressure or the outlet-side pressure and are consequently moved into a position in which the control bodies 88 open the respective power control opening Release or close 70.

Furthermore, the arrangement of the control channel 82 and the division thereof into an inlet-side section 122 and an outlet-side section 124 ensure that all control pistons 84a to 84d which are arranged successively from the inlet side are always in the position connecting their power control openings 70a to 70d to the return flow channel 72 stand, since all of the branch channels 80a to 80d open into the inlet-side section 122.

Furthermore, it is ensured that all control pistons 84e to 84h arranged in the direction of the outlet are in their position closing the respective power control openings 70e to 70h, since their branch channels 80e to 80h open into the outlet-side section 124 of the control channel 82.

Because the power control openings 70a to 70d, as shown for example in FIG. 3, are connected on the one hand to the return flow channel 72 and thus via this to the inlet 50 and on the other hand the power control openings 70a to 70d open into the screw chamber 12, the power control openings 70a to 70d act as if the recess 56 of the inlet 50 would extend to the power control opening 70d so that the compressor has a lower power.

Depending on how many of the control pistons 84a to 84h are in a position in which the corresponding control bodies 88 open the corresponding output control openings 70, the output of the screw compressor according to the invention can be controlled, in particular an essentially continuously variable output control being possible when the Power control openings 70a to 70h have an extension in the axial direction 68 which corresponds at most to a distance between the screw combs 15 and 17 and the distance between successive power control openings 70a to 70h approximately corresponds to the distance between successive screw combs 15, 17 up to a maximum of twice the distance between them.

The increments still present are determined by the extension of the power control openings 70a to 70h in the axial direction 68, so that a reduction in this extension also reduces these increments.

The control takes place by moving the slide 120 in the control channel 82 by means of an actuating device 130, which acts on the slide 120 via a push rod 132.

In the position of the slide 120 shown in FIG. 4, all the control pistons 84a to 84h are in a position in which the corresponding control bodies 88 open the power control openings 70a to 70h and connect them to the channel 72.

In a preferred variant of the solution according to the invention, a check valve 134 is additionally provided in the connecting channel 114, which always allows pressure relief of the inlet-side section 122 of the control channel 82, however, no pressure reaction from the inlet 50 to the inlet-side section 122 of the control channel 82. There is thus the possibility that moving the slide 120 to enlarge the inlet-side section 122 therein can lower the control pressure below the inlet-side pressure and thus with such a movement of the Before the compressor starts, slide 120 ensures that all control pistons 84 are positioned in such a way that the control bodies open the power control openings and thus the screw compressor requires only a low starting torque.

Each of the control pistons 84 is further provided with an annular groove 140 which, in the position of the control piston 84, in which the control body 88 does not close the corresponding power control opening 70, is aligned with an opening 142 to the annular groove 140 of the next control piston 70 and the annular groove 140a is also aligned of the control piston 84a closest to the inlet 50 with an injection channel 144 for injecting a medium or oil.

In addition, each of the control pistons 84 is provided with an injection opening 146, which is followed by a bore 148 axially penetrating the piston 84, which in turn opens into a transverse bore 150, the opening 152 of which is in the position of the piston 84, in which the control body 88 the power control opening 70 closes, is aligned with the opening 142 to the preceding piston 84, so that a medium to be injected can flow from the opening 142 through the bores 150 and 148 to the injection opening 146 and exit therefrom.

As shown in FIG. 3, the ring channels 140a, 140b, 140c and 140d together with the openings 142 between the ring channel 140a, the ring channel 140b, the ring channel 140c and the ring channel 140d form a channel system in continuation of the injection channel 144, so that ultimately of the annular channel 140d, the medium to be injected can pass through the opening 142 between the annular channel 140d and the opening 152 in the control piston 84e and can flow through the bores 150 and 148 in this control piston 84e to the injection opening 146, the control piston 84e closing the power control opening 70 in its opening Position at the same time ensures that a connection to the opening 142 between the piston bore 76e and the piston bore 76f is interrupted.

Through the annular channels 140 and the openings 142, a channel system is thus created which, as viewed from the inlet, simultaneously uses the first control piston 84e closing the power control opening 70e in order to inject a medium into the compression spaces 40 or 42 formed above the injection opening 146.

Such a medium can be, for example, ECO gas from an economizer system or also oil.

The screw compressor according to the invention also has an over-compression control opening 170 which is close to the outlet opening 54 and is arranged in the wall region 66 and which on the one hand opens into the screw chamber 12 and on the other hand into an outlet duct 172 leading to the outlet 52.

The over-compression control opening 170 is also adjoined by a piston bore 176 which projects into the housing body 74 and extends to a bottom surface 178, a branch duct 180 also opening into this bottom surface 178 opening from the outlet-side section 124 of the control duct 82. A control piston 184 arranged in the piston bore 176 likewise comprises a control body 188 which can be inserted into the overcompression control opening 170 for closing the same. The control body 188 also has an end face 190 facing the screw chamber 12, which is adapted to the wall surface 38 in the region of the over-compression control opening 170, so that when the over-compression control opening 170 closes the position of the control body 188 above the end face 190, a zero-volume volume is formed.

The control piston 184 also has a piston surface 186, a control cylinder chamber 200 being formed between the piston surface 186, the bottom surface 178 and the section of the piston bore 176 lying between them, in the same way as in the control piston 84, which is always subjected to control pressure, which corresponds to a pressure in the outlet 52.

In the same way as in the case of the control piston 84, the control piston 184 also has an annular surface 198 surrounding the control body 188, which extends up to an outer surface 202 of the control body 188, which is designed such that it fits into a cylindrical surface 192 of the over-compression control opening 170 is insertable to close it with the control body 188.

The control piston now works in such a way that the control pressure corresponding to the discharge pressure on the piston surface 186 leads to a force which holds the control body 188 in its position closing the over-compression control opening 170, since in normal cases a maximum pressure acts on the end face 190 thereof without over-compression , which can be at most equal to the outlet pressure. The resultant force is always smaller than the force generated by the control pressure due to the smaller end surface 190 than the piston surface 186.

However, if the pressure on the outlet side drops and becomes lower than the pressure originally specified by the maximum compression ratio, over-compression would occur. In this case, however, the regulating pressure can become smaller than the pressure acting on the end face 190 through the compression spaces 40, 42, and consequently the regulating piston 184 moves in the direction away from the screw chamber 12 so that the over-compression regulating opening through the regulating body 188 does not medium compressed to the maximum compression ratio can flow to the outlet 52 through the outlet channel 172, thereby avoiding over-compression.

In the first exemplary embodiment, each of the screw bodies 14 and 16 is assigned a series of power control openings 70a to 70h and an overcompression control opening 170, as shown in FIG. 5.

In all cases, the central axis 94 or 194 of the respective piston bore 76 or 176 is preferably arranged radially to the corresponding axis of rotation 30 or 32.

In contrast, in a variant of the solution according to the invention, shown in FIG. 6, it is provided that each screw body 14 or 16 is assigned two rows of power control openings 70 ′ or 70 ″ in order to enlarge the flow cross section of the power control openings.

Otherwise, the control bodies 88 'and 88' 'and the control pistons 84' and 84 '' are designed in the same way as described in connection with the first exemplary embodiment, but in this case the central axes 94 'and 94' 'are the same Piston bores 76 'or 76' 'are no longer formed radially to the respective screw body 14, but rather parallel to one another, however, the central axes 94' of one row 70 'and the central axes 94' 'of the other row 70' 'are each in one plane.

Claims (45)

Screw compressor for gas circuits, in particular for refrigeration systems, comprising a compressor housing with an inlet and an outlet for the medium to be compressed, two screw bodies arranged in a screw chamber of the compressor housing and extending between the inlet and the outlet, which with the formation of between the inlet and the Interlocking closed compression spaces
characterized in that in a wall region (66) of the screw chamber (12) which delimits compression spaces (40, 42) which are closed at maximum output, a plurality of power control openings (70) are provided, each of which has locations of this wall region (66) corresponding to different compression ratios, each of which has a of several separately operable control bodies (88) can either be closed in that the control body (88) essentially fills the power control opening (70), or can be connected to a return flow channel (72) connected to the inlet (50) in that the control body ( 88) is at a distance from the power control opening (70). Screw compressor according to claim 1, characterized in that the control bodies (88) can be moved transversely to a cross-sectional area of the respective power control opening (70) in the direction away from the screw chamber (12). Screw compressor according to claim 1 or 2, characterized in that the control bodies (88) have an end face (90) with which the respective power control opening (70) in the closed position of the control bodies (88) of the wall surface (38) of the screw chamber (12 ) can be locked accordingly in this area. Screw compressor according to one of the preceding claims, characterized in that a plurality of power control openings (70) is assigned to each screw body (14, 16). Screw compressor according to one of the preceding claims, characterized in that the power control openings are arranged along a line lying in the wall surface (66) of the screw chamber (12). Screw compressor according to claim 5, characterized in that the power control openings (70) are arranged in a row parallel to the axial direction (30, 32). Screw compressor according to one of the preceding claims, characterized in that all control bodies (88) are of identical design. Screw compressor according to one of claims 5 to 7, characterized in that the center distances between successive power control openings (70) is less than twice the distance between successive screw combs (60). Screw compressor according to one of claims 5 to 8, characterized in that the power control openings (70) extend in the direction of the line over at least half the distance between successive screw combs (60) of the screw bodies (14, 16). Screw compressor according to one of the preceding claims, characterized in that a drive element (84) is assigned to each control body (88). Screw compressor according to claim 10, characterized in that the drive element (84) for closing the power control opening (70) by the control body (88) acts on the latter with a force proportional to the pressure on the outlet side. Screw compressor according to claim 11, characterized in that the drive element (84) is actuated by pressure medium. Screw compressor according to claim 12, characterized in that the drive element (84) for transferring and / or holding the control body (88) in its position closing the power control opening (70) can be actuated with a medium which is under a control pressure proportional to the outlet-side pressure. Screw compressor according to claim 12 or 13, characterized in that the drive element (84) in the position of the control body (88) connecting the respective power control opening (70) to the return flow channel (72) can be acted upon with a control pressure proportional to the inlet-side pressure. Screw compressor according to one of claims 12 to 14, characterized in that each drive element has a control piston (84), on which on the one hand the local pressure in the screw chamber (12) acts at the location of the respective power control opening and on the other hand the control pressure. Screw compressor according to claim 15, characterized in that each control body (88) is part of the respective control piston (84). Screw compressor according to one of claims 15 or 16, characterized in that all control pistons (84) are of identical design. Screw compressor according to claims 15 to 17, characterized in that the control pistons (84) are arranged in the compressor housing (10) in bores (76) running transversely to the axial direction (30, 32) of the screw bodies (14, 16). Screw compressor according to claim 18, characterized in that the bores (76) with their axes (94) run parallel to one another. Screw compressor according to claim 19, characterized in that the axes (94) of the bores (74) lie in one plane. Screw compressor according to one of claims 15 to 20, characterized in that the control pistons (84) are designed such that their side facing away from the control body (88) has a piston surface (86) which can be acted upon by the control pressure and delimits a control cylinder chamber (110). Screw compressor according to one of the preceding claims, characterized in that a power control device is provided which opens all compression ratios corresponding to power control openings corresponding to a selected compression ratio and closes all compression ratios corresponding to power control openings corresponding to or above the selected compression ratio. Screw compressor according to claim 22, characterized in that the control cylinder chambers (110) of different control bodies (88) are connected to different outputs (80) of a power control device (82, 120) which specifies control pressures at the outputs (80). Screw compressor according to claim 23, characterized in that the power control device has a movable control slide (120) with which selected outputs (80) of the power control device can be acted upon with different control pressures. Screw compressor according to claim 24, characterized in that the control slide (120) is arranged in a control channel (82) and by the control slide (120) the control channel is divided into an outlet-side section (124) in which the pressure proportional to the outlet-side pressure is as Control pressure is present, and an inlet-side section (122), in which a maximum pressure proportional to the inlet-side pressure is present as the control pressure, and that the individual control cylinder chambers (110) are connected to the latter via outputs (80) branching off from different locations of the control channel (82) . Screw compressor according to claim 25, characterized in that a check valve blocking a gas flow from the inlet (50) into the inlet-side section (122) is arranged between the inlet-side section (122) of the control channel (82) and the inlet (50). Screw compressor according to one of the preceding claims, characterized in that the control bodies (88) are provided with an injection opening (146) for injecting a medium into one of the compression spaces (40, 42) which are formed, and in that the injection opening (146) one of the respective output control openings (70) closing control body (88) can be connected to an injection channel (144). Screw compressor according to Claim 27, characterized in that the injection opening (146) of the control body (88) which comes closest to the selected compression ratio with its compression ratio and is in its position closing the power control opening (70) is connected to the injection channel (144). Screw compressor according to claim 27 or 28, characterized in that the connection between the injection opening (146) and the injection channel (144) can be controlled by the position of the control body (88) relative to the power control opening (70). Screw compressor according to claim 27 or 28, characterized in that each control body (88) in its position connecting the power control opening (70) with the inlet (50) connects the next following control body (88) corresponding to a higher compression ratio with the injection channel (144) . Screw compressor according to one of claims 27 to 30, characterized in that each control body (88) in its position closing the power control opening (70) connects the injection opening (146) of the next control body (88) corresponding to a higher compression ratio with the injection channel (144 ) interrupts. Screw compressor according to one of the preceding claims, characterized in that an overcompression control opening (170) is provided in a wall area (66) of the screw chamber (12) delimiting compression chambers with high compression ratios and can be closed with a control body (188) in a first position thereof and in a second position of the same can be connected to the outlet (52) and that the control body (188) is acted upon elastically by a force proportional to the pressure on the outlet side. Screw compressor according to claim 32, characterized in that each screw body (14, 16) is assigned at least one over-compression control opening (170). Screw compressor according to claim 32 or 33, characterized in that the control body (188) is designed such that in its first position it essentially fills the over-compression control opening (170). Screw compressor according to claim 34, characterized in that the regulating body (188) is designed such that its end face (190) in the first position thereof the respective over-compression regulating opening (170) with one of the wall surface (38) of the screw chamber (12) in this area appropriate surface closes. Screw compressor according to one of claims 32 to 35, characterized in that the regulating body (188) can be moved transversely to the end face (190) of the overcompression regulating opening (170). Screw compressor according to one of claims 32 to 36, characterized in that all control bodies (188) are of identical design. Screw compressor according to one of claims 32 to 37, characterized in that the regulating body (188) is part of a regulating piston (184), on the one hand the local pressure in the screw chamber (12) at the location of the over-compression regulating opening (170) and on the other hand that on the outlet side Pressure proportional force acts. Screw compressor according to claim 38, characterized in that all control pistons (184) are of identical design. Screw compressor according to claim 37 or 38, characterized in that the control piston (184) has on its side opposite the control body (188) a piston surface (186) which is acted upon by a pressure proportional to the pressure on the outlet side. Screw compressor according to claim 37 or 39, characterized in that the control piston (184) is arranged in a piston bore (176) in the compressor housing (10). Screw compressor according to claim 41, characterized in that the piston bores (176) with their axes (194) run parallel to one another. Screw compressor according to claim 42, characterized in that the axes of the piston bores (176) lie in one plane. Screw compressor according to one of claims 39 to 43, characterized in that the control pistons (184) and the control pistons (84) are of identical design. Screw compressor according to claim 44, characterized in that the axes of the piston bores (176) and the bores (76) lie in one plane.

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