OIL-INJECTED VACUUM PUMP ELEMENT

Abstract

An oil-injected vacuum pump element, whereby two mating helical rotors are rotatably provided in a housing, whereby this housing comprises an inlet port and an outlet end face with an outlet port, whereby compression chambers are formed between the helical rotors and the housing, wherein the vacuum pump element is provided with a connection that extends from a first compression chamber to a second smaller compression chamber at the outlet end face, whereby this first compression chamber is at a lower pressure than the second compression chamber and whereby this second compression chamber can make connection with the outlet port upon rotation of the helical rotors, whereby the connection is such that a flow from the second compression chamber to the first compression chamber is possible, whereby the connection is not directly connected to the outlet port.

Claims

1-9. (canceled)

10. An oil-injected vacuum pump element of the screw type, whereby two mating helical rotors are rotatably provided in a housing, whereby this housing comprises an inlet port, an inlet end face and an outlet end face with an outlet port, whereby compression chambers are formed between the helical rotors and the housing that proceed from the inlet port to the outlet port due to the rotation of the helical rotors and thereby become increasingly smaller, wherein the oil-injected vacuum pump element is provided with a connection that extends from a first compression chamber to a second smaller compression chamber at the outlet end face, whereby this first compression chamber is at a lower pressure than the second compression chamber and whereby this second compression chamber can make connection with the outlet port upon rotation of the helical rotors, whereby the connection is such that a flow from the second compression chamber to the first compression chamber is possible so that the pressure in the second compression chamber is reduced, whereby the connection is not directly connected to the outlet port.

11. The oil-injected vacuum pump element of the screw type according to claim 10, wherein the first compression chamber makes contact with the inlet port and with the outlet end face.

12. The oil-injected vacuum pump element according to claim 10, wherein the aforementioned connection is realised by means of a groove that is affixed in the outlet end face, whereby this groove extends from the first compression chamber to the second compression chamber.

13. The oil-injected vacuum pump element according to claim 12, wherein the groove at least comprises a slot-shaped straight or curved section.

14. The oil-injected vacuum pump element according to claim 13, wherein next to the aforementioned slot-shaped section, the groove comprises a broadened section with which the groove at least partially overlaps the first compression chamber.

15. The oil-injected vacuum pump element according to claim 10, wherein the aforementioned connection is realised by means of a groove part in the outlet end face that at least partially overlaps the second compression chamber, and a channel or pipe connected thereto that leads to the first compression chamber, whereby this channel or this pipe is built in the housing or otherwise.

16. The oil-injected vacuum pump element according to claim 10, wherein the minimum cross-section of the connection in mm.sup.2 is between 0.01 and 0.1 times the maximum volumetric flow of the element in litres per second, preferably between 0.01 and 0.08 times, even better between 0.01 and 0.06 times and more preferably between 0.01 and 0.04 times.

17. The oil-injected vacuum pump element according to claim 10, wherein the end of the connection that is connected to the second compression chamber at the outlet end face is designed such that the maximum contact area between the connection and the aforementioned second compression chamber has an area in mm.sup.2 of between 0.01 and 0.1 times the maximum volumetric flow of the element in litres per second, preferably 0.01 and 0.08 times, even better between 0.01 and 0.06 times and more preferably between 0.01 and 0.04 times.

18. The oil-injected vacuum pump element according to claim 10, wherein the overlap between the connection and the first compression chamber is such that the connection between the first compression chamber and the second compression chamber is preserved upon rotation of the helical rotors until the volume of the second compression chamber goes to zero or practically zero.

Description

[0027] With the intention of better showing the characteristics of the invention, a few preferred embodiments of an oil-injected vacuum pump element according to the invention are described hereinafter by way of an example, without any limiting nature, with reference to the accompanying drawings, wherein:

[0028] FIG. 1 schematically shows an oil-injected vacuum pump element of the screw type;

[0029] FIG. 2 schematically shows a cross-section of the oil-injected vacuum pump element of FIG. 1 along the line II-II of FIG. 1;

[0030] FIG. 3 shows a similar cross-section to FIG. 2, but of an oil-injected vacuum pump element according to the invention;

[0031] FIG. 4 shows the cross-section of FIG. 3, but in a different position of the helical rotors;

[0032] FIGS. 5 to 7 show alternative embodiments of FIG. 3.

[0033] The oil-injected vacuum pump element 1 shown in FIG. 1 is an element of the screw type.

[0034] The element 1 essentially comprises a housing 2 in which two cooperating helical rotors 3 are rotatably provided.

[0035] The housing 2 comprises an inlet end face 4 on the inlet side 5 and an outlet end face 6 on the outlet side 7.

[0036] An inlet port 8 is affixed in the housing 2. This inlet port 8 is indicated by a dashed line in FIG. 1.

[0037] An outlet port 9 is affixed in the housing at the location of the outlet end face 6. This is shown in FIG. 2. Compression chambers 11a, 11b are formed between the lobes 10 of the helical rotors 3 and the housing 2. Due to the rotation of the helical rotors 3 these compression chambers 11a, 11b move from the inlet port 8 to the outlet port 9.

[0038] For as long as the compression chamber 11a, 11b makes contact with the inlet port 8, its volume will increase, so that a suction of gas is created.

[0039] When the compression chamber 11a, 11b is no longer in contact with the inlet port 8, the volume of the compression chambers 11a, 11b will decrease upon further rotation of the helical rotors 3 so that the gas, for example air, is compressed in these chambers.

[0040] Air that gets into a compression chamber 11a via the inlet port 8 in the first compression phase is transported to the outlet port 9 by the rotation of the helical rotors 3 and is thereby compressed to a higher pressure.

[0041] At a certain time during the rotation of the helical rotors the compression chamber 11b will make contact with the outlet port 9 so that the compressed air in this compression chamber 11b can be removed during the last compression phase.

[0042] The accompanying compression chambers 11a, 11b that belong to the two aforementioned compression phases, i.e. a first compression chamber 11a that makes contact with the inlet port 8 and the outlet end face 6 and a second compression chamber 11b that only makes contact with the outlet end face 6 but not with the inlet port 8 or the inlet end face 4, are indicated in FIG. 2.

[0043] As can be seen in this drawing these two compression chambers 11a, 11b are separated from one another by one single section of the helical rotors 3, whereby a channel 12 with a nozzle shape is formed between the profiles of the helical rotors 3.

[0044] A flow of air and/or oil is possible via this channel 12 in the direction from the second compression chamber 11b to the first compression chamber 11a, whereby due to the form of the channel 12 the flow speed becomes so high that cavitation can occur.

[0045] In an oil-injected vacuum pump element 1 according to the invention, as shown in FIG. 3, a connection is affixed in the outlet end face, in this case in the form of a groove 13.

[0046] This groove 13 extends from the first compression chamber 11a to the second compression chamber 11b.

[0047] Hereby a first end 14a of the groove 13 will at least partially overlap the first compression chamber 11a and a second end 14b of the groove 13 will overlap the second compression chamber 11b.

[0048] A flow of gas and/or oil from the second chamber 11b, at a higher pressure, is possible via this groove 13 to the first compression chamber 11a so that the pressure in the second compression chamber 11b is reduced.

[0049] In this way the pressure in the second compression chamber 11b can be prevented from becoming too high such that the flow of gas and/or oil will be slower via the aforementioned channel 12.

[0050] In this way cavitation, and the detrimental consequences thereof, is prevented.

[0051] Although in the example shown the groove 13 makes contact with a first compression chamber 11a that is connected to the inlet port 8, this is not necessarily the case. It is only necessary for the invention that the first compression chamber 11a concerned, to which the groove 13 is connected, is at a lower pressure than the second compression chamber 11b.

[0052] According to the invention the connection is designed such that the groove 13 is not directly connected to the outlet port 9.

[0053] This can clearly be seen in FIG. 3: the groove 13 stops at some distance from the outlet port 9 so that there is no contact with the second end 14b of the groove 13 and the outlet port 9.

[0054] This will ensure that a direct leakage flow is not possible from the outlet port 9 to the inlet port 8 via the groove and the first compression chamber 11a, whereby this leakage flow negatively affects the efficiency of the oil-injected vacuum pump element 1.

[0055] In the situation of FIG. 3 the second end 14b of the groove 13 is not in contact with the second compression chamber 11b. Upon further rotation of the helical rotors 3, whereby the second compression chamber 11b becomes increasingly smaller, this end 14b will increasingly overlap the second compression chamber 11b. As a result, the pressure increase in the second compression chamber 11b will be counteracted, because this chamber is still in contact with the first compression chamber 11a by means of the groove 13, so that a flow of gas and/or oil is possible from the second compression chamber 11b to the first compression chamber 11a.

[0056] FIG. 4 shows the situation whereby the volume of the second compression chamber 11b has gone to practically zero. Hereby the second end 14b of the groove 13 is still connected to the second compression chamber 11b.

[0057] At this moment the pressure in the second compression chamber 11b can become very high, but the pressure in the second compression chamber 11b will be low enough to prevent cavitation through the connection to the first compression chamber 11a by means of the groove 13.

[0058] The location of the second end 14b, by which the groove 13 makes contact with the second compression chamber 11b, must be suitably chosen such that a connection to the second compression chamber 11b is realised without coming into contact with the outlet port 9.

[0059] The final location of the groove 13, and in particular the second end 14b, will depend on the rotor profiles and the shape of the outlet port 9.

[0060] The final form and size of the groove 13 and thus the flow rate of gas and/or oil that can flow via the groove 13 will depend on two criteria: [0061] the flow rate must be high enough so that the pressure in the second compression chamber 11b can fall enough to prevent cavitation; [0062] the flow rate may not be too high because in this case the performance or efficiency of the oil-injected vacuum pump element 1 will fall.

[0063] The flow rate that can flow via the groove 13 will depend on the minimum cross-section of the groove 13.

[0064] Preferably this minimum cross-section of the groove 13 in mm.sup.2 is between 0.01 and 0.04 times the maximum volumetric flow of the element 1 in litres per second.

[0065] However, it is not excluded that this minimum cross-section in mm.sup.2 is between 0.01 and 0.1 or 0.01 and 0.08 or 0.01 and 0.06 times the maximum volumetric flow of the element 1 in litres per second.

[0066] A groove 13 with a smaller minimum cross-section will not be able to allow sufficient flow to let the pressure in the second compression chamber 11b fall enough to prevent cavitation.

[0067] A groove 13 with a larger minimum cross-section will allow through the large flows from the second compression chamber 11b to the first compression chamber 11a, such that the efficiency of the oil-injected vacuum pump element 1 will fall by too much.

[0068] Preferably the end 14b of the groove 13 that is connected to the second compression chamber 11b at the outlet end face 6 is designed such that the maximum contact area between the groove and the aforementioned compression chamber 11b has an area in mm.sup.2 between 0.01 and 0.04 times the maximum volumetric flow of the element 1 in litres per second.

[0069] It is not excluded that the aforementioned maximum contact area is between 0.01 and 0.1 or 0.01 and 0.08 or 0.01 and 0.06 times the maximum volumetric flow of the element 1 in litres per second.

[0070] As it is possible that the contact area between the groove 13 and the second compression chamber 11b is less than the minimum cross-section of the groove 13 itself, preferably it is sufficient for the aforementioned contact area to be at the higher stated condition, in order to obtain the desired effect.

[0071] Different options are possible with regard to the final design of the groove 13.

[0072] Preferably the groove comprises at least one slot-shaped section 15.

[0073] Slot-shaped 15 section here means a part of the groove 13 whose cross-section, viewed in the flow direction through the groove 13, does not change or practically does not change.

[0074] This section 15 can be straight or curved.

[0075] In FIGS. 3 to 6 the groove 13 only comprises a slot-shaped section 15.

[0076] As can be seen in these drawings, the slot-shaped groove 13 has different orientations.

[0077] It is also possible that the groove 13 connecting to this slot-shaped section 15 comprises a broadened section 16, whereby the groove 13 at least partially overlaps the first compression chamber 11a.

[0078] This is shown in FIG. 7, where it can be seen that the first end 14a of the groove 13 is formed by a broadened section 16 with a wider cross-section than the second end 14b that is formed by a slot-shaped section 15.

[0079] The precise shape of this broadened section 16 is of secondary importance.

[0080] The only condition for the first end 14a is that this end 14a extends far enough so that the groove 13 is always connected to the first compression chamber 11a.

[0081] Preferably the overlap between the groove 13 and the first compression chamber 11a is such that the connection between the first compression chamber 11a and the second compression chamber 11b is preserved by means of the groove 13 upon the rotation of the helical rotors 2 until the volume of the second compression chamber 11b goes to zero.

[0082] At this moment the pressure in the second compression chamber 11b is very high and the second compression chamber 11b is no longer connected to the outlet port 9, such that the high pressure in this second compression chamber 11b can only escape via the aforementioned nozzle-shaped channel 12.

[0083] In order to prevent this it is ensured that the second compression chamber 11b is connected to the first compression chamber 11a, and thus the inlet port 8, by means of the groove 13.

[0084] In this way the pressure in the second compression chamber 11b can be prevented from becoming too high during this phase at the time that the volume in this compression chamber 11b goes to zero and cavitation can be prevented.

[0085] Although in the examples shown above, the connection is always made by means of a groove 13 in the outlet end face 6, it is not excluded that the connection is realised by means of a groove part in the outlet end face 6 that at least partially overlaps the second compression chamber 11b and a channel or pipe connected thereto that leads to a first compression chamber 11a at a lower pressure than the second compression chamber 11b.

[0086] As already stated, this compression chamber 11a can be the compression chamber 11a that is connected to the inlet port 8, but this is not the necessary for the invention.

[0087] This channel or this pipe can be built in housing itself or otherwise, but of course can also be constructed on the housing.

[0088] In such an embodiment, preferably it must be ensured that the minimum cross-section of the groove part and the channel and the maximum contact area between the groove part and the second compression chamber 11b both satisfy the above-mentioned conditions, i.e. this minimum cross-section and this maximum contact area in mm.sup.2 is between 0.01 and 0.1 times the maximum volumetric flow of the element 1 in litres per second, and preferably between 0.01 and 0.08 times, even better between 0.01 and 0.06 times, and even more preferably between 0.01 and 0.04 times.

[0089] The aforementioned groove part can take on the form of the slot-shaped section 15 of the groove 13 for example, as shown in FIG. 7.

[0090] Preferably it is also ensured that the channel or the pipe is such that the connection between the first compression chamber 11a and the channel or the pipe is preserved upon rotation of the helical rotors 3 until the volume of the second compression chamber 11b goes to zero.

[0091] The present invention is by no means limited to the embodiments described as an example and shown in the drawings, but a an oil-injected vacuum pump element according to the invention can be realised in all kinds of forms and dimensions without departing from the scope of the invention.