SCREW COMPRESSOR WITH ROTOR ENDPLATES

Field of the Invention

The present invention relates to a screw compressor primarily for gaseous refrigerants, which screw compressor comprises a compressor housing, which comprises a male and a female screw rotor arranged in screw rotor bores in. the compressor housing, which male and female rotor are co-rotatingly driveable and interact to compress the refrigerant, where the compressor housing is connected to a bearing housing, where rotor endplates are placed between the screw rotors and the bearing housing, which rotor endplates comprise cutouts for discharge ports.

Background of the Invention

US 6,409,490 describes a screw compressor, which screw compressor comprises guide bushings mounted within bores for the bearings to support the compressor rotor shafts. First bushings are provided at an inlet casing of the compressor and provide guidance for a slide stop, and second bushings are provided in an outlet casing of the compressor to provide guidance for a slide valve. The bushings are also mounted to the inlet and outlet casings to provide centring of two sections of the compressor rotor housing.

Object of the Invention It is the object of the invention to assemble a screw compressor with optimal alignment of the rotors in the compressor housing and in relation to a bearing housing.

A further object is to achieve alignment of the compressor housing with a bearing housing avoiding guiding pins or bolts.

Description of the invention

This can be achieved with a compressor as described in the preamble to claim one, if the endplates comprise outer diameters, which respective diameters significantly exceed the corresponding rotor diameters which outer diameter of the endplates cooper- ates with recesses in the compressor housing and with recesses in the bearing housing.

Hence it is achieved that alignment of the rotors in relation to the compressor housing and towards the bearing housing takes place by the rotor endplate. The rotor endplate is formed in a groove, which groove is formed partly as a recess in the compressor housing and partly as a recess in the bearing housing. This can lead to alignment of the bearing housing towards the compressor housing without using further components.

Thus, there is no need for guiding pins or bolts in the assembly. In fact the bearing housing and the compressor housing are free to deviate in size simply because they are optimally aligned towards each other. Hence, both components are more tolerant than usual.

It is preferred that the first and the second endplates comprise oil channels to lead oil towards their inner boring, where oil nozzles are formed in the endplates between the channels and the inner boring to form an oil film between the rotor shafts and the bor- ing in the endplates, which oil films further lubricate the rotor bearings at the discharge end of the compressor. Hence, a very efficient lubrication can be achieved of not only the endplate and the rotor shaft but also of the bearings at the pressure side of the screw compressor.

The clearance between the rotor shaft and the endplates can generate limited oil flow to seal the axial clearances between the rotors and the endplates. Hence, it is achieved that the oil flow for lubricating the bearing is reduced to a level of oil which does not disturb the bearings.

The rotor endplates can be formed with circular recesses around their central opening to allow an oil film to get access to the inside of the bearings. The female rotor is formed with a rolling bearing and a ball bearing. The male rotor is formed with a bearing placed opposite the female rotor, as the roller bearing has to be placed near the driving shaft. This way the bearing itself can carry the weight of the rotor of a rela- tively heavy electric motor.

Labyrinth sealing can be formed between the inner opening in the endplates and the rotor shafts. This way it can be achieved that the oil flow is further reduced to a level which is sufficient for efficient lubrication of the bearings.

The endplates can comprise a number of oil channels for oil distribution inside in the compressor. A number of channels can be formed in the endplate to distribute oil not only in the neighbourhood of the endplates but also to distribute oil for different purposes in the compressor. One example is a shaft seal where particular channels in, the bearing housing are necessary to lead high pressure oil towards a shaft seal. Furthermore, the oil channels in the compressor housing will lead oil towards the rotors for rotor lubrication. The compressor housing oil channels will lead oil towards the suction end of the rotors to achieve a balancing pressure generated by oil at the male screw rotor, which is pressed towards the shaft end of the rotor. Furthermore, the oil is used to lubricate the bearings at the rotor suction end. Finally, oil channels can be used for hydraulic activation of a slider, which slider can co-operate with the rotors.

At least one of the endplates can comprise at least one boring connected to oil channels, where the boring comprises a pressure control valve. The pressure control valve can be used to let oil into different areas of the compressor to operate at different pressures. The highest oil pressure is usually applied for the shaft sealing. Reduced pressure oil is applied for most of the different purposes previously mentioned.

One of the endplates can comprise channels connected to an economizer port, which port can be connected to a medium pressure in a refrigeration system, where refrigerant at medium pressure flows through channels in at least one of the endplates towards an inlet, where a low or medium pressure level is present in the compressor. Hence it is achieved mat refrigerant which for one or another reason has evaporated in the refrigeration system can be led back towards the compressor and thus be mixed with the refrigerant pressurized in the screw compressor.

One of the endplates can also comprise channels connected to a high pressure liquid injection port. The injection of liquid refrigerant at an intermediate pressure will lead to a temperature reduction and cooling of the rotors, as the liquid refrigerant evapo- rates. Depending on the operation parameters of a refrigeration system, liquid refrigerant at a relatively high pressure can be present in e.g. a receiver, where the amount of liquid refrigerant in some situations can be relatively high and where a reduction of the level takes place without influencing the operation of the refrigeration system

negatively. The liquid refrigerant can in this situation be led from the piping directly to the compressor for cooling of the compression process.

Description of the Drawing Fig. 1 shows a sectional view of a screw compressor, Fig. 2 shows a sectional view of a female endplate, Fig. 3 shows a male rotor endplate, Fig. 4 shows a sectional view of fig. 3.

Detailed Description of the invention

Fig. 1 shows a sectional view of a screw compressor 2 comprising a compressor housing 4, which compressor housing 4 comprises rotor borings 6 for screw rotors 8 and 10. An oil inlet is indicated by 12 in a bearing housing 14. Between the bearing housing 14 and the compressor housing 4 rotor endplates 16 and 18 are placed. The male rotor 8 has a driving shaft 24, which driving shaft 24 co-operates with a shaft sealing 26 placed in the bearing housing 14. The bearing housing 14 further comprises a roller bearing 28 and a ball bearing 30. The female rotor 10 has a shaft 32, which shaft 32 co-operates with the bearing housing 14 through a ball bearing 34 and a roller bearing 36. At the suction end of the male rotor the male rotor has a shaft 40, which shaft 40 is supported by a roller bearing 42. The female rotor 10 also has a shaft 44 at the suction side. The shaft 44 is supported through a roller bearing 46. The shaft 40 of the male rotor 8 co-operates with a bushing 48 between which bushing 48 and the housing a pressure chamber 50 is formed.

Fig. 2 shows a sectional view of a female endplate 302, which female endplate is known as number 16 in fig. 1. The female endplate 302 has a planar side 307 in which planar side 307 a channel 316 is indicated. Furthermore, an inlet 312 for oil is indicated. The oil inlet is connected to an opening 314 intended for a pressure reduction valve. The outlet from the pressure reduction vale is connected to a channel 306. A central rotor shaft opening 308 comprises a circular oil channel 310, which circular channel 310 is connected to a very small opening in the oil channel 316. At the side of the female discharge plate is seen a cutout 304, which cutout 304 is connected to the channel 206 indicated in fig. 4.

Fig. 3 shows a male rotor endplate 330, which is indicated as number 18 in fig. 1. An oil channel 332 is indicated, which oil channel communicates with the oil supply in the compressor housing. Another opening is indicated as 334, which opens towards an internal channel known as channel 338 in fig. 7. The male rotor endplate furthermore has a discharge opening 336 and a central opening 338 for a rotor shaft.

Fig. 4 shows a sectional view of fig. 3. The sectional view is seen from lines B-B and thus shows channel 338, which has a very small opening 340 for supplying the inner bearing with oil. The oil channel 338 continues, and oil can leave the endplate through an opening 342.