Lubricated rotary compressor having a cooling medium inlet to the delivery port

A rotary compressor such as a screw-type or a spiral compressor comprises a compressor stator and one or more rotary compression elements, which compressor stator is provided with a suction port, a delivery port and a lubricant inlet, the lubricant being intended for lubricating each compression element, for sealing the gaps between the individual compression elements and between the compression elements and the compressor stator, and for cooling the medium to be compressed during the compression process. The compressor also comprises an inlet for a cooling medium for cooling the lubricant which opens out near or in the delivery port.

FIELD OF THE INVENTION 
The invention relates to a rotary compressor such as a screw-type or a 
spiral compressor, comprising a compressor stator and one or more rotary 
compression elements, which compressor stator is provided with a suction 
port, a delivery port and a lubricant inlet, the lubricant being intended 
for lubricating each compression element, for sealing the gaps between the 
individual compression elements and between the compression elements and 
the compressor stator, and for cooling the medium to be compressed during 
the compression process, and also comprising a device for cooling the 
lubricant by injecting a cooling medium. 
BACKGROUND OF THE INVENTION 
Such a rotary compressor is known from German Patent 2,261,336. In this 
case the lubricant, which is discharged from the compressor together with 
the compressed medium, is cooled by injecting a cooling medium. Due to the 
fact that this cooling medium evaporates in the space in which the mixture 
is compressed, the temperature of said mixture falls, which means that the 
oil temperature also falls. 
This known method of cooling has the disadvantage that cooling medium in 
liquid form leaks through the gaps to be sealed with lubricant, as a 
result of which loss of output occurs. A second disadvantage is that the 
cooling medium disrupts the lubrication of the compression elements during 
the compression process, which reduces the operating reliability of the 
compressor. 
In the absence of a device for cooling the lubricant in the compressor a 
heat exchanger is built into the system, taking up quite a large amount of 
space. This heat exchanger is then situated between the oil separating 
device and the lubricant injection point on the compressor. 
SUMMARY OF THE INVENTION 
The object of the invention is therefore to provide a compressor of the 
type mentioned above, in which optimum cooling of the lubricant is 
ensured, without the output and the operating reliability being adversely 
affected, while the size of the device required for the purpose can still 
remain limited. This is achieved through the fact that the device for 
cooling the lubricant comprises a cooling medium inlet opening out near or 
in the delivery port. 
The compressed mixture leaving the compressor via the delivery port has a 
high degree of turbulence. Since the cooling medium is injected precisely 
at this point, a thorough mixing of the mixture and the cooling medium is 
obtained in a short time and over a short distance. This ensures a rapid 
and reliable cooling of the mixture through the evaporating cooling 
medium. This is necessary to prevent cooling medium from being discharged 
in the liquid state into the oil separating device, with the risk of 
liquid cooling medium being fed to the compressor instead of lubricant, 
for example at the position of the bearings. 
The cooling of the compressed mixture could also take place through 
injection of cooling medium liquid at a point downstream of the delivery 
port. The turbulence will, however, in that case be much less strong, 
which is less advantageous for rapid cooling. 
In the known device for cooling the compressed mixture the cooling action 
can be improved by generating turbulence in, for example, the delivery 
pipe between compressor and oil separator. This is, however, accompanied 
in most cases by a fall in pressure, which adversely affects output. 
The invention can be used for any type of rotary compressor. Beneficial 
results can be obtained in particular in this respect in the case of a 
twin-screw compressor which is provided with a compressor stator with a 
gastight outer shell and an inner double cylindrical housing, in which the 
housing has at least one bore opening out in or near the delivery port. 
The cooling medium can be fed to the bore by means of a pipe which opens 
out with one end on the outside of the shell, and is connected at the 
other end to the bore. 
Since the shell and the housing of the compressor reach a different 
temperature during operation, expansion differences will occur between 
them. The cooling medium inlet therefore preferably has a flexible part 
between shell and housing for absorbing said expansion differences. 
Particularly good results are obtained if the housing has three bores which 
are distributed regularly at an angle of essentially 90.degree. over the 
half of the housing facing away from the delivery aperture opening out 
laterally on the housing. These three bores mean, on the one hand, that 
sufficient cooling medium can be fed in while, on the other, the diameter 
of the bores can remain limited. This is important for maintaining the 
mechanical strength of the housing at a sufficiently high level. 
Each bore preferably runs in a plane at right angles to the axis of 
rotation of the compressor elements. This ensures that the injected 
cooling medium does not go between said compressor elements, which would 
adversely affect their operation.

DETAILED DESCRIPTION OF THE INVENTION 
In the diagram shown in FIG. 1 the screw compressor according to the 
invention is indicated by 1. The cooling medium is compressed by means of 
this screw compressor 1. The cooling medium mixed with lubricant passes 
through the delivery pipe 2 into the oil separating device 3, in which the 
lubricant is separated from the gaseous, compressed cooling medium. The 
cooling medium then flows through the condenser 4, in which condensation 
occurs, following which expansion takes place at 5. Finally, vaporisation 
occurs in the cooling element 6, with the result that the desired cooling 
effect is obtained. The vaporised, gaseous cooling medium then flows back 
to the screw compressor 1, following which the cycle described above is 
repeated. 
According to the invention, the liquefied cooling medium is now injected 
through pipe 7 and pump 8 in or near the delivery port 9 of the screw 
compressor 1. A very good mixing of the cooling medium with the mixture 
supplied through the screw compressor 1, composed of compressed cooling 
medium and oil, is obtained as a result. The cooling liquified medium 
vaporising in the delivery port 9 and fed in through pipe 7 can 
consequently exert an excellent cooling influence on the mixture 
compressed by the screw compressor 1, with the result that already after a 
length of pipe 2 of one meter the oil has reached the desired temperature. 
Oil can be fed to the oil injection points and the bearings of the 
compressor by means of oil pump 22. 
FIG. 2 shows a cross-section through a twin-screw compressor, at the level 
of the compression elements 10, 11 in the form of screws. The screw 
compressor has an outer shell 12 and an inner double cylindrical housing 
13, which are rigidly connected to each other. The screws 10 and 11 are 
supported in the known manner and are also driven in the known manner by 
shaft 14. The arrows 15 indicate the infeed of the medium to be 
compressed, and the arrow 16 indicates the discharge. Of course, the 
medium to be compressed is sucked in through the suction port and is 
discharged from the screw compressor through the delivery port, which is 
shown schematically at 17. As further shown in FIG. 2, feed elements 18 
open out in this delivery port 17, through which elements a cooling 
liquified medium for cooling the compressed mixture coming out of the 
screw compressor and also containing oil is fed in. 
FIG. 3 shows more clearly how these elements 18 are fitted. Bores 19 are 
first provided for the purpose in the double cylindrical housing 13, which 
bores open out into the delivery port 17 at one side and onto the outside 
of said double cylindrical housing at the other side. A pipe 20 is 
connected there to each bore, said pipe opening out via a screw coupling 
21 onto the outside of the outer shell 12 of the screw compressor. 
The cooling liquified medium can be injected by means of the feed elements 
18 into the delivery port, where the compressed mixture, which also 
contains oil, is in a very turbulent state. This means that the cooling 
liquified medium is directly mixed with that mixture, with the result that 
a good heat exchange is obtained. 
The pipes 20 can be flexible, in order to ensure that expansion differences 
between the outer shell 12 and the double cylindrical housing 13 cannot 
lead to breakage.