WO2011048618A1

WO2011048618A1 - Screw compressor with variable compression ratio

Info

Publication number: WO2011048618A1
Application number: PCT/IT2009/000472
Authority: WO
Inventors: Mr.Gianni Candio; Mr. Matteo Iobbi; Mr. Diego Portinari
Original assignee: Refcomp Spa
Priority date: 2009-10-19
Filing date: 2009-10-19
Publication date: 2011-04-28

Abstract

The. invention is a screw compressor (1) comprising: a container body (2); two rotors (3, 4) arranged in the container body (2) with the respective rotation axes (X1, X2) mutually parallel, provided on corresponding side surfaces (6, 7) with helical grooves (5) that mesh with each other to delimit corresponding compression chambers; drive means suited to set the rotors (3, 4) rotating in opposite directions and to compress a fluid contained in the compression chambers; a suction duct (11) and an outlet duct (12) for the fluid, communicating with the compression chambers at the level of corresponding inlet and outlet ends (9, 10) of the rotors (3, 4); shutter means (13) interposed between the rotors (3, 4) and the outlet duct (12). The shutter means (13) comprise a through opening (14) made in the container body (2), arranged so that it faces the side surface (6, 7) of the rotors (3, 4) and associated with a shutter unit (17) suited to open and close the through opening (14).

Description

SCREW COMPRESSOR WITH VARIABLE COMPRESSION RATIO

DESCRIPTION

The present invention concerns a screw compressor particularly suited to compress the operating fluid of a cooling system.

As is known, a screw compressor generally comprises a container body housing two rotors with mutually parallel rotation axes.

The side surface of each rotor is provided with helical grooves that mesh with the helical grooves provided on the other rotor, in such a way as to delimit, at the level of the mutually meshing areas, a series of compression chambers suited to contain a gas to be compressed, for example a refrigerant.

Due to the helical shape of the grooves, the rotation of the rotors causes the compression chambers, and therefore the fluid contained therein, to move from an inlet end of the rotors to an outlet end.

The helical grooves are shaped so that the volume of each compression chamber progressively reduces during the rotation of the rotors, thus compressing the fluid during the above mentioned movement between the two ends of the rotors.

From an operational point of view, the fluid to be compressed flows into the compression chambers through a suction duct that communicates with the compression chambers at the level of the inlet end of the rotors.

The fluid is then compressed between the rotors and finally discharged through a outlet duct arranged in proximity to the outlet end.

The compression ratio of such a compressor depends on the ratio between the volume of the compression chamber at the level of the rotors' inlet end and the volume of the same compression chamber at the level of the outlet end, immediately before the fluid is discharged.

In particular, the discharge of the compressed fluid from each compression chamber starts at the moment when, during the rotation of the rotors, the compression chamber opens toward the outlet duct.

The above mentioned discharge moment is determined with precision via shutter means interposed between the rotors and the discharge duct, which comprise an outlet port whose position determines the compression ratio.

It is clear that, the more said moment is advanced, the lower the compression ratio will be.

In many systems, in particular in cooling systems, it is necessary to be able to vary the above mentioned compression ratio in real time, based on the load conditions of the system itself.

According to a known method, the compression ratio is modified by varying the position of the outlet port with respect to the outlet end of the rotors.

In particular, the above mentioned outlet port is obtained in a valve body arranged against the rotors and sliding parallel to their longitudinal axis.

The sliding movement of the valve body modifies the position of the outlet port with respect to the rotor axis, thus making it possible to vary the moment in which the discharge begins and therefore also the compression ratio.

In the construction form described above the rotors and the valve body must practically be arranged in mutual contact in order to ensure satisfying tightness, in such a way as to avoid the untimely discharge of the fluid during the compression stage.

A first drawback posed by this construction form is represented by the vibrations produced by the contact between the valve body and the grooves of the rotors during rotation.

The contact between the valve body and the rotors causes a further drawback represented by the fact that, in case of malfunction, the valve body may interfere with the rotors, thus damaging them to the point of stopping the compressor.

Stopping the compressor means causing the whole system to stop, which is obviously a further drawback.

The present invention intends to overcome all the drawbacks of the known art as outlined above.

In particular, it is the object of the present invention to develop a screw compressor provided with means for adjusting the compression ratio, in which possible interferences of the above mentioned adjusting means with the rotors are avoided.

It is also the object of the invention to provide adjusting means that are simple to make.

It is a further, yet not the least object of the invention, to provide adjusting means that allow a precise and reliable adjustment of the compression ratio. The above mentioned objects are achieved by a screw compressor carried out according to the main claim.

Further characteristics and details of the invention are indicated in the corresponding dependent claims.

Advantageously, the invention reduces the risk of damage to the rotors and stoppage of the system in case of malfunction of the adjusting means, given that the latter do not interfere with the rotors.

Furthermore, advantageously, the absence of interferences between the two components avoids the production of vibrations caused by the impact of the helical grooves of the rotors with the adjusting means.

Still advantageously, the reliability of the adjustment of the compression ratio brings higher efficiency and regularity of operation of the system.

The said, objects and advantages, together with others which will be highlighted below, are illustrated in the description of a preferred embodiment of the invention which is provided by way of non-limiting example with reference to the attached drawings, wherein:

Figure 1 shows an axonometric view of the compressor that is the subject of the invention;

Figure 2 shows a partial section view of the compressor shown in Figure 1 ;

Figure 3 shows an axonometric section view of a detail of the compressor shown in Figure 1 ;

Figure 4 shows a plan view of the section of Figure 3;

- Figure 5 shows the exploded axonometric view of some components of the compressor of Figure 1 ;

Figures from 6 to 9 show the detail of Figure 3, in a side section view and in different operating configurations.

The compressor that is the subject of the invention is shown in Figure 1 and indicated as a whole by 1.

As shown in the section view of Figure 2, it comprises a container body 2 housing two rotors 3 and 4 arranged with the respective rotation axes X1 and X2 mutually parallel.

Each rotor is provided with helical grooves 5 on the respective side surface, which mesh with the helical grooves of the opposed rotor in order to delimit corresponding compression chambers suited to contain the fluid to be compressed.

Drive means are also provided which are suited to set the rotors 3, 4 rotating in opposite directions, not illustrated in the figure but known per se.

The drive means preferably set rotating a first drive rotor 3 via the shaft 3a, while the second rotor 4 is driven by the first rotor owing to the fact that they mesh with each other.

The helical grooves 5 can be in any known shape, provided that they define compression chambers with decreasing volumes from an inlet end 9 of the rotors 3, 4 towards an outlet end 10 opposite the iniet end 9.

In this way, the rotation of the rotors 3, 4 determines the compression of the fluid contained in the compression chambers, during its movement from the inlet end 9 to the outlet end 10.

The compressor 1 also comprises a fluid suction duct 11 and a fluid outlet duct 12, communicating with the compression chambers at the level of the above mentioned inlet end 9 and outlet end 10, respectively.

Shutter means 13 are also provided, interposed between the rotors 3, 4 and the outlet duct 12 in order to allow the compression ratio of the compressor 1 to be adjusted.

According to the invention, the above mentioned shutter means 13 comprise a plurality of through openings 14, made in the container body 2 and arranged facing the side surfaces 6, 7 of the two rotors 3, 4.

Said through openings 14 are more evident in the section view of Figure 3, where the rotors 3, 4 have been removed.

A first series 15 of through openings preferably faces the first rotor 3, while a second series 16 of through openings faces the second rotor 4, in such a way as to allow one compression chamber to be emptied via two through openings 14 at the same time.

It cannot be excluded that construction variants of the invention may comprise a single series of through openings, facing only one of the above mentioned rotors 3, 4.

The position of the different through openings 14 of one same series is such that they communicate with the compression chambers at respectively different moments during the rotation of the respective rotor 3, 4, said different instants corresponding to different volumes of the compression chambers.

This can be obtained, for example, by arranging the through openings 14 aligned along the rotation axis X1 , X2 of the corresponding rotor 3, 4, at gradually increasing distances with respect to the outlet end 10, as can be observed in particular in Figure 4.

The compressor 1 also comprises a shutter unit 17 associated with the above mentioned through openings 14 and suited to selectively open and close them. It is clear that opening and closing one or more of the above mentioned through openings 14 via the shutter unit 17 means modifying the moment at which the compressed fluid starts to be discharged from each compression chamber, so as to vary the compression ratio of the compressor 1.

Furthermore, the shutter unit 17 and the rotors 3, 4 are separated owing to the interposition of the container body 2, as shown in Figures from 6 to 9, even though they communicate with each other via the through openings 14.

Therefore, the invention achieves the object to avoid interferences between the movement of the rotors 3, 4 and the movement of the shutter unit 17.

In particular, to advantage, the vibrations due to the impacts between the grooves of the rotors 3, 4 and the shutter unit 17 are eliminated.

Still advantageously, any malfunctions of the shutter unit 17 do not affect the operation of the compressor 1.

It is evident, in fact, that in case of malfunction of the shutter unit 17, the only consequence will be that it is not possible to adjust the compression ratio, while the rotors 3, 4 can continue to operate in any case, without any risk of damage or stoppage.

By way of non-limiting example, the compressor 1 illustrated herein includes three through openings 14 for each one of the series 15 and 16.

It is evident, however, that in each series the number of through openings 14 and the distance between them can be any number and any distance, such details being decided by the manufacturer according to the desired compression ratios.

Therefore, it is clear that the arrangement of the above mentioned openings 14 in predefined positions makes it possible to precisely define the compression ratios that can be obtained, thus achieving the object to ensure the reliability of the adjustment operation.

The container body 2 preferably but not necessarily comprises a further opening 25, facing the front surface 8 of the rotors 3, 4 at the level of their outlet end 10.

The above mentioned opening 25 defines the maximum compression ratio reached by the compressor 1 when all the through openings 14 are closed by the shutter unit 17, as shown in Figure 9, and is preferably always open, so as to avoid overpressures in the compressor 1. Each through opening 14 is preferably configured in such a way as to be able to communicate with one single compression chamber at a time.

In this way, it is possible to advantageously prevent a through opening 14 from placing two adjacent compression chambers at different pressures in communication, which would cause unwanted lowering of the average discharge pressure of the compressed fluid.

For this purpose, as shown in Figure 4, the through openings 14 are elongated in shape according to a longitudinal development direction Y that, with respect to the rotation axes X1 and X2, has substantially the same inclination as the helical grooves 5 of the corresponding rotor 3, 4 when they are directed towards the openings 14.

For the same reason, the two series of openings 15 and 16 are preferably offset in the direction of the rotation axes X1, X2 of the rotors, of a distance equal to the offset distance between the corresponding helical grooves 5 on the two rotors 3, 4 that is necessary for them to mesh with each other.

The shutter unit 17 is structured so as to assume different operating configurations, in each one of which the shutter unit closes a corresponding predefined number of through openings 14, as respectively shown in Figures from 6 to 9.

In particular, the succession of the above mentioned operating configurations determines the opening of a gradually increasing number of through openings 14, starting from the one nearest to the outlet end 10 and proceeding towards the farthest one.

In order to obtain the above, the shutter unit 17 preferably comprises a shaped body 18 arranged against the container body 2, on the opposite side with respect to the rotors 3, 4, as shown in Figure 5, which is an exploded view of the shutter means 13.

The above mentioned shaped body 18 is slidingly associated with the container body 2 according to a sliding direction Z such that the shaped body 18, during the above mentioned sliding movement, can be arranged so as to face any of the through openings 14 and close it.

The shaped body 18 is preferably delimited at one end 18a by two surfaces 19 and 20, each one parallel to the longitudinal directions Y1 and Y2 of corresponding series of through openings 15 and 16.

Therefore, with two series 15, 16 of through openings 14, the end of the shaped body 18 assumes the "V" shape shown in Figure 5.

Advantageously, the shape described above of the shaped body 18 makes it possible to open only one through opening 14 at a time, with a limited movement of the shaped body 18.

Consequently, to advantage, it is possible to provide several through openings 14 arranged near each other, thus increasing the number of compression ratios that can be achieved.

The shaped body 18 is operatively connected to an actuator 21 that defines the above mentioned sliding direction Z and that is preferably a fluid-operated cylinder 22 in which a plunger 23 is slidingly housed.

The fluid-operated cylinder 22 preferably comprises a plurality of supply ducts 24 for a service fluid, for example the lubricating oil of the compressor 1 , each one of which communicates with the cylinder 22 in a different axial position, said supply ducts being schematically indicated in Figure 2.

The supply ducts 24 are associated with corresponding areas whose pressure is predefined via the same number of valves, which can be selectively opened to introduce or discharge the service fluid into/from various points of the cylinder 22, in such a way as to determine different axial positions of the plunger 23, corresponding to the above mentioned operating configurations of the shutter unit 17.

A possible embodiment of the fluid-operated cylinder 22 and of the corresponding supply ducts 24, which makes it possible to determine various axial positions of the plunger 23, is described in the European patent application EP 1 730 406, filed on 02/03/2005 in the name of the same holder of the present application.

On the other hand, it is evident that, in construction variants of the invention not illustrated herein, the actuator 21 can be of a type different from the one described above, for example electro-mechanical, provided that it allows the shutter unit 17 to be arranged in any one of the above mentioned operating configurations.

In any case, since adjustment takes place discretely, it is clear that the shutter unit 17 does not require particular devices to control with precision, moment by moment, the position of the shaped body 18.

This simplifies the compressor 1 of the invention compared to compressors of known type, in which the adjustment of the compression ratio takes place continuously.

From an operational point of view, to obtain a given compression ratio among those envisaged, the shutter unit 17 is arranged in the corresponding operating configuration, in such a way as to close a given number of through openings 14 and leave the others open, as schematically shown in Figures from 6 to 9. During the rotation of the rotors 3, 4, each compression chamber opens onto the outlet duct 12 at the moment in which the corresponding helical grooves 5 reach the open through opening 14 that is nearest to the inlet end 9.

The position of the shutter unit 17 can be modified in such a way as to open further through openings 14 arranged more upstream, in such a way as to advance the above mentioned discharge moment and reduce the compression ratio of the compressor 1, until reaching the configuration shown in Figure 6, which is the one with the lowest compression ratio.

On the contrary, closing one or more through openings 14 means increasing the compression ratio.

If all the through openings 14 are closed, the fluid is discharged only through the front opening 25, with the highest compression ratio, as shown in Figure 9. The compressor 1 described above is particularly suited to be coupled with a variable speed motor, known per se, which makes it possible to obtain maximum flexibility from the compressor 1.

In fact, while the shutter unit 17 makes it possible to vary the compression ratio, the variable speed motor allows the flow rate of the compressed fluid to be varied.

It is therefore clear that such a compressor 1 can advantageously adapt, in real time, to different operational loads of the system on which it is installed. The above clearly shows that the compressor of the invention achieves all the set objects.

In particular, the fact that the rotors are separated from the shutter unit makes it possible to avoid interferences between the two elements, avoiding vibrations, as well as possible stoppages of the compressor and damages to the rotors.

Furthermore, the use of through openings makes it possible to obtain a reliable and precise adjustment of the compression ratio, with particularly simple adjusting means.

Upon implementation, the compressor that is the subject of the invention may be subjected to further changes that, even if not described herein and not illustrated in the drawings, must all be considered protected by the present patent, provided that they fall within the scope of the following claims.

In the cases where the technical characteristics illustrated in the claims are followed by references, these have been added only with the aim to facilitate the comprehension of the claims themselves and therefore said references do not have any limiting effect on the degree of protection to be granted to each element they identify only by way of example.

Claims

1) Screw compressor (1) comprising:

- a container body (2);

- two rotors (3, 4) arranged in said container body (2) with the corresponding rotation axes (X1 , X2) mutually parallel, provided with helical grooves (5) provided on the corresponding side surfaces (6, 7) and meshing with each other to delimit corresponding compression chambers;

- drive means suited to set said rotors (3, 4) rotating in opposite directions to compress a fluid contained in said compression chambers;

- a suction duct (11) for said fluid, communicating with said compression chambers at the level of an inlet end (9) of said rotors (3, 4);

- an outlet duct (12) for the compressed fluid, communicating with said compression chambers at the level of an outlet end (10) of said rotors (3, 4), opposite said inlet end (9);

- shutter means (13) interposed between said rotors (3, 4) and said outlet duct (12);

characterized in that said shutter means (13) comprise at least one through opening (14) made in said container body (2), arranged so that it faces the side surface (6, 7) of at least one of said rotors (3, 4) and associated with a shutter unit (17) suited to open and close said through opening (14).

2) Compressor (1) according to claim 1), characterized in that it comprises a plurality of said through openings (14), aligned' along the rotation axis (X1 , X2) of the corresponding rotor (3, 4).

3) Compressor (1) according to claim 2), characterized in that it comprises a first series (15) of said through openings (14) facing a first one of said rotors (3) and a second series (16) of said through openings (14) facing a second one of said rotors (4).

4) Compressor (1) according to claim 3), characterized in that the through openings (14) of said first series (15) are offset with respect to the through openings (14) of said second series (16) according to a direction parallel to said rotation axes (X1 , X2).

5) Compressor (1) according to any one of the preceding claims, characterized in that each one of said through openings (14) defines a longitudinal development direction (Y1 , Y2) having, with respect to said rotation axes (X1 , X2), an inclination that is substantially equal to the inclination of the helical grooves (5) of the corresponding rotor (3, 4).

6) Compressor (1) according to any one of the claims from 2) to 5), characterized in that said shutter unit (17) is structured in such a way as to assume a plurality of different operating configurations, each one of which determines the closure of a corresponding predefined number of said through openings (14).

7) Compressor (1) according to any one of the preceding claims, characterized in that said shutter unit (17) comprises a shaped body (18) arranged against said container body (2) on the opposite side with respect to said rotors (3, 4).

8) Compressor (1) according to claim 7) when in combination with claim 5), characterized in that said shaped body (18) is delimited at one end (18a) by a surface (19, 20) parallel to the longitudinal direction (Y1 , Y2) of said through openings (14).

9) Compressor (1) according to any one of claims 7) or 8), characterized in that said shaped body (18) is slidingly associated with said container body (2) according to a sliding direction (Z) that is such that said shaped body (18) can be arranged facing any one of said through openings (14) while sliding in said sliding direction (Z).

10) Compressor (1) according to claim 9), characterized in that said shutter unit (17) comprises an actuator (21) operatively connected to said shaped body (18) in order to define said sliding direction (Z).

11) Compressor (1) according to claim 10), characterized in that said actuator (21) is a fluid-operated cylinder (22) in which a plunger (23) is slidingly housed.

12) Compressor (1) according to claim 1 ), characterized in that said fluid-operated cylinder (22) comprises a plurality of supply ducts (24) for a service fluid, each one of which communicates with said fluid-operated cylinder (22) in a different axial position.

13) Compressor (1) according to any one of the preceding claims, characterized in that said container body (2) comprises a further opening (25) facing the front surfaces (8) of said rotors (3, 4) at the level of said outlet end (10).