• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    Oil-injected vacuum pump element, two cooperating screw rotors (3) being rotatably mounted in a housing (2), said housing (2) comprising an inlet port (8) and an outlet head face (6) with an outlet port (9), between the screw rotors ( 3) and the housing (2) compression chambers (11a, 11b) are formed, characterized in that the vacuum pump element (1) is provided with a connection that extends from a first compression chamber (11a) to a second, smaller compression chamber (11b) ) at the exhaust end face (6), which first compression chamber (11a) is at a lower pressure than the second compression chamber (11b) and which second compression chamber (11b) can communicate with the exhaust port (3) upon rotation of the screw rotors (3) 9), the connection being such that a flow is possible from the second compression chamber (11b) to the first compression chamber (11a), the connection not communicating directly with the outlet port (9) .
    公开号:BE1022764B1
    申请号:E2015/5137
    申请日:2015-03-12
    公开日:2016-08-30
    发明作者:Jens BOECKX；Jozef Maria Segers
    申请人:Atlas Copco Airpower Naamloze Vennootschap；
    IPC主号:
    专利说明:

    Oil-injected vacuum pump element.
    The present invention relates to an oil-injected vacuum pump element.
    More specifically, the invention is intended for oil-injected vacuum pump elements of the screw type, wherein two co-operating screw rotors are rotatably mounted in a housing.
    Chambers are defined between the lobes of the screw rotors and the walls of the housing, which rotate from the inlet side to the outlet side by rotating the rotors and thereby become smaller and smaller so that the air trapped in these chambers is compressed.
    It is known that oil is injected into the compression chamber of such elements to dissipate the compression heat, to lubricate the screw rotors, to prevent corrosion and to provide a seal between the rotors.
    This oil comes from an oil separation where the oil is separated from the exhaust air.
    It is impossible to remove all air from the oil, so that oil is injected that contains a certain air content.
    This air content can be in the form of air bubbles or can be dissolved in the oil.
    This creates a risk of cavitation. There are two types of cavitation in an oil flow: ~ cavitation in which oil vapor bubbles are formed because the static pressure drops below the vapor pressure of the oil; - cavitation in which air bubbles are formed in oil flows that contain a certain amount of air, because a decrease in the static pressure reduces the solubility of air in the oil.
    Regardless of the type of cavitation, damage can occur if the air bubbles or oil vapor bubbles thus formed implode in the vicinity of (metal) parts. This damage can be very extensive and can lead to the destruction of the machine.
    Such cavitation under the influence of a drop in the static pressure can occur in an oil-injected screw-type vacuum pump element, more particularly at the outlet of the vacuum pump in the final phase of compression.
    In the final phase of the compression, the volume of the compression chamber goes to zero, so that the pressure in this chamber can rise above the outlet pressure. This results in large pressure differences between the aforementioned chamber and the inlet, where the pressure can be 0.3 mbar (a) and lower.
    During the final phase of compression, the pre-trimmed chamber is separated from another compression chamber that connects to the inlet by only a single section of the rotor profiles.
    In this section, a kind of channel forms between the profiles of the rotors or between the rotors and the outlet head surface that first converges and then diverges, to form a 'nozzle'.
    Via this channel a leakage flow of gas and oil is possible from the aforementioned chamber to the inlet due to the large pressure difference between the two, whereby due to the shape of the channel and the rotors the speed of this leakage flow becomes so great that the static pressure becomes so low that gas bubbles can arise.
    Further in the channel, the static pressure rises again, causing the bubbles formed to implode, causing damage to the rotors and the housing. Due to this damage, the vacuum pump element will no longer function properly.
    The present invention has for its object to provide a solution to the aforementioned and other disadvantages.
    The present invention has as an object an oil-injected screw-type vacuum pump element, wherein two cooperating screw rotors are rotatably mounted in a housing, which housing comprises an inlet port, an inlet head face and an outlet head face with an outlet port, compression chambers being formed between the screw rotors and the housing which, due to rotation of the screw rotors, move from the entry gate to the outlet port and thereby become smaller and smaller, the oil-injected vacuum pump element being provided with a connection extending from a first compression chamber to a. second, smaller compression chamber at the outlet head face, which first compression chamber is at a lower pressure than the second compression chamber and which second compression chamber can come into contact with the outlet port upon rotation of the screw rotors, the connection being such that a flow of the second compression chamber to the first compression chamber is possible so that the pressure in the second compression chamber is reduced, the connection not being directly connected to the outlet port.
    The rotation of the screw rotors causes the first compression chamber to become smaller and smaller and eventually to the second compression chamber, a new first compression chamber being formed at this time.
    The second compression chamber is the compression chamber at the end of the compression cycle, which contains compressed gas which can then leave the vacuum pump element via the outlet port. It goes without saying that this second compression chamber is not connected to the inlet port.
    An advantage of an oil-injected vacuum pump element according to the invention is that the pressure difference between the inlet and the second compression chamber is reduced by allowing a flow of gas and oil via the connection from the second compression chamber at higher pressure to the first compression chamber at a lower busy.
    Cavitation can hereby be avoided because the flow via the channel between the profiles of the screw rotors or the flow between the rotors and the outlet head surface. in the section of the rotor profiles that separates the aforementioned second compression chamber from the compression chamber in communication with the inlet, will have a much lower speed.
    After all, due to the reduced pressure in the second compression chamber, the pressure difference across the aforementioned channel is too small to cause a flow through the channel that can give rise to cavitation.
    The precise location of the connection and its shape will depend on the profile of the screw rotors and on the shape and location of the outlet port. Both can vary greatly depending on the vacuum pump element in question.
    In any case, it must be avoided that the connection is in contact with the outlet port, that is, the connection may not connect directly to the outlet port.
    With the insight to better demonstrate the features of the invention, a few preferred embodiments of an oil-injected vacuum pump element according to the invention are described below as an example without any limiting character, with reference to the accompanying drawings, in which: figure 1 schematically shows an oil-injected vacuum pump element of the screw type; figure 2 schematically represents a cross-section of the oil-injected vacuum pump element of figure 1 along the line II-II in figure 1; figure 3 represents a cross-section similar to figure 2, but of oil-injected vacuum pump element according to the invention; figure 4 represents the cross-section of figure 3, but in a different position of the screw rotors; Figures 5 to 7 represent alternative embodiments of Figure 3.
    The oil-injected vacuum pump element 1 shown in Figure 1 is a screw-type element.
    The element 1 essentially comprises a housing 2 in which two cooperating screw rotors 3 are arranged for rotation.
    The housing 2 comprises an inlet head face 4 on the inlet side 5 and an outlet head face 6 on the outlet side 7.
    An inlet port 8 is provided in the housing 2. This inlet port 8 is indicated by a dotted line in Figure 1.
    At the location of the outlet head surface 6, an outlet port 9 is provided in the housing. This is shown in Figure 2.
    Compression chambers 11a, 11b are formed between the lobes 10 of the screw rotors 3 and the housing 2. By rotating the screw rotors 3, these compression chambers 11a, 11b move from the inlet port 8 to the outlet port 9.
    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.
    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 with further rotation of the screw rotors 3, so that the gas, for example air, is compressed in these chambers.
    Air which, via the inlet port 8, enters a compression chamber 11a in the first phase of compression, is transported by rotation of the screw rotors 3 to the discharge port 9 and thereby compressed to a higher pressure.
    At a certain moment during the rotation of the screw rotors 3, the compression chamber 11b will come into contact with the outlet port 9 so that the compressed air in this compression chamber 11b can be discharged during the final phase of compression.
    The associated compression chambers 11a, 11b belonging to the two aforementioned compression phases, namely a first compression chamber 11a which makes contact with the inlet port 8 and the outlet head face 6 and a second compression chamber 11b which only makes contact with the outlet head face 6 but not with the inlet port 8 or the inlet end face 4, are indicated in Figure 2.
    As can be seen in this figure, these two compression chambers 11a, 11b are separated from each other by means of a single section of the screw rotors 3, a channel 12 having a "nozzle" shape forming between the profiles of the screw rotors 3.
    Via this channel 12 a flow of air and / or oil is possible in the direction from the second compression chamber 11b to the first compression chamber 11a, whereby the flow rate becomes so high that cavitation can occur due to the shape of the channel 12.
    In an oil-injected vacuum pump element 1 according to the invention, as shown in Figure 3, a connection is provided in the outlet head face, in this case in the form of a groove 13.
    This groove 13 extends from the first compression chamber 11a to the second compression chamber 11b.
    Here, a first end 14a of the groove 13 will at least partially overlap with the first compression chamber lia and a second end 14b of the groove 13 will overlap with the second compression chamber 11b.
    Via this groove 13 a flow of gas and / or oil from the two compression chamber 11b, at a higher pressure, to the first compression chamber 11a is possible so that the pressure in the second compression chamber 11b is lowered.
    In this way it can be avoided that the pressure in the second compression chamber 11b becomes too high, as a result of which the flow of gas and / or oil via the aforementioned channel 1.2 will be slower.
    In this way, cavitation and its adverse consequences are avoided.
    Although in the example shown the groove 13 makes contact with a first compression chamber 11a which is connected to the inlet port 8, this is not necessarily the case. It is only necessary for the invention that the relevant first compression chamber 11a with which the groove 13 is connected is at a lower pressure than the second compression chamber 11b.
    According to the invention, the connection is designed such that the groove 13 is not directly connected to the outlet port 9.
    This is clearly visible in Figure 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.
    This will ensure that no direct leakage current is possible from the outlet port 9 to the inlet port 8 via the groove 13 and the first compression chamber 11a, which leakage current negatively influences the efficiency of the oil-injected vacuum pump element 1.
    In the state in Figure 3, the second end 14b of the groove 13 is just in communication with the second compression chamber 11b. With a further rotation of the screw rotors 3, in which the second compression chamber 11b becomes increasingly smaller, this end 14b will increasingly overlap with the second compression chamber 11b. This prevents the pressure increase in the second compression chamber 11b, because this chamber is still in communication 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.
    Figure 4 shows the situation in which the volume of the second compression chamber 11b has virtually gone to zero. The second end 14b of the groove 13 is still in communication with the second compression chamber 11b.
    At this time, the pressure in the second compression chamber 11b can become very high, but via the connection to the first compression chamber 11a by means of the groove 13, the pressure in the second compression chamber 11b will be low enough to prevent cavitation.
    The location of the second end 14b, with which the groove 13 makes contact with the second compression chamber 11b, must be appropriately selected so that a connection with the second compression chamber 11b is realized, without coming into contact with the outlet port 9.
    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.
    The final shape and size of the groove 13 and thus the flow of gas and / or oil that can flow through the groove 13 will depend on two criteria: - the flow must be large enough so that the pressure in the second compression chamber 11b can be enough bags to avoid cavitation; - the flow rate must not be too large because in this case the efficiency or efficiency of the oil-injected vacuum pump element 1 will decrease.
    The flow that can flow through the groove 13 will depend on the minimum cross-section of the groove 13.
    This minimum diameter in mm 2 of the groove 13 is preferably between 0.01 and 0.04 times the maximum volumetric flow of the element 1 in liters per second.
    However, it is not excluded that this minimum diameter in mm2 is between 0.01 and 0.1 or 0.01 and 0.08 or 0.01 and 0.06 times the maximum volumetric flow rate of the element 1 in liters per second .
    A groove 13 with a smaller minimum cross-section will not be able to allow sufficient flow to allow the pressure in the second compression chamber 11b to drop sufficiently to prevent cavitation.
    A groove 13 with a larger minimum cross-section will allow the large debits to pass from the second compression chamber 11b to the first compression chamber 11a, so that the efficiency of the oil-injected vacuum pump element 1 will fall too much.
    Preferably, the end 14b of the groove 13 in communication with the second compression chamber 11b on the outlet head surface 6 is designed such that the maximum contact surface between the groove and the aforementioned compression chamber 11b has a surface area in mm 2 between 0.01 and 0.04 times the maximum volumetric flow rate of the element is 1 in liters per second.
    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 rate of the element 1 in liters per second.
    Since it is possible for the contact surface between the groove 13 and the second compression chamber 11b to be smaller than the minimum cross-section of the groove 13 itself, the aforementioned contact surface preferably also satisfies the aforementioned condition in order to achieve the desired effect.
    Regarding the final design of the groove 13, various options are possible.
    The groove preferably comprises at least one slot-shaped portion 15.
    By slot-shaped portion is here meant a part of the groove 13, the cross-section of which, as seen in the flow direction through the groove 13, does not change or hardly changes.
    This portion 15 can be straight or curved.
    In Figures 3 to 6, the groove 13 only comprises a slot-shaped portion 15.
    As can be seen in these figures, the slot-shaped groove 13 can have different orientations.
    It is also possible that the groove 13 connecting to this slot-shaped part 15 comprises a widening part 16 with which the groove 13 at least partially overlaps with the first compression chamber 11a.
    This is shown in Figure 7, where it can be seen that the first end 14a of the groove 13 is formed by a widening portion 16 with a wider cross-section than the second end 14b formed by a slot-shaped portion 15.
    The precise shape of this broadening portion 16 is of secondary importance.
    The only condition for the first end 14a is that this end 14a extends far enough so that the groove 13 always remains in communication with the first compression chamber 11a.
    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 maintained by means of the groove 13 upon rotation of the screw rotors 3 to the volume of the second compression chamber 11b goes to zero.
    At this time, 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, so that the high pressure in this second compression chamber 11b can only escape via the aforementioned "nozzle" -shaped channel 12 .
    To avoid this, it is ensured that the second compression chamber 11b is in communication with the first compression chamber 11a, and thus the inlet port 8, through the groove 13.
    In this way it will be possible to prevent the pressure in the second compression chamber 11b becoming too high in this phase as well, at the moment that the volume in this compression chamber 11b goes to zero and cavitation can be avoided.
    Although in the examples shown above, the connection was always made by means of a groove 13 in the outlet head face 6, it is not excluded that the connection is realized by means of a groove part in the outlet head face 6 which at least partially overlaps with the second compression chamber 11b and a connecting channel or conduit leading to a first compression chamber 11a at a lower pressure than the second compression chamber 11b.
    As already mentioned, this compression chamber 11a may be the compression chamber 11a in communication with the inlet port 8, but this is not necessary for the invention.
    This channel or pipe may or may not be built into the housing itself, but can of course also be built up on the housing.
    Also in such an embodiment, it should preferably be ensured that the minimum cross-section of the groove part and the channel and the maximum contact surface between the groove part and the second compression chamber 11b both satisfy the above-mentioned conditions, namely that this minimum cross-section and this maximum contact area in mm 2 between 0.01 and 0.1 times the maximum volumetric flow rate of the element is 1 in liters per second, and preferably between 0, 01 and 0.08 times, more preferably between 0.01 and 0.06 times and preferably between 0.01 and 0.04 times.
    The aforementioned groove part can for instance take the form of the slot-shaped part 15 of the groove 13 as shown in figure 7.
    Also, it is preferably ensured that the channel or conduit is such that the connection between the first compression chamber 11a and the channel or conduit is maintained during the rotation of the screw rotors 3 until the volume of the second compression chamber 11b goes to zero .
    The present invention is by no means limited to the embodiments described as examples and shown in the figures, but an oil-injected vacuum pump element according to the invention can be realized in all shapes and sizes without departing from the scope of the invention.
    权利要求:
    Claims (8)
    [1]
    Conclusions.
    1. - Oil-injected screw-type vacuum pump element, wherein two co-operating screw rotors (3) are rotatably arranged in a housing (2), which housing (2) has an inlet port (8), an inlet head face (4) and an outlet head face (6). comprises an outlet port (9), wherein compression chambers (11a, 11b) are formed between the screw rotors (3) and the housing (2} which rotate from the inlet port (8) to the outlet port (9) by rotation of the screw rotors (3) and thereby becoming smaller and smaller, characterized in that the oil-injected vacuum pump element (1) is provided with a connection extending from a first compression chamber (11a) to a second, smaller compression chamber (11b) on the outlet head face (6), which first compression chamber (11a) is at a lower pressure than the second compression chamber (11b) and which second compression chamber (11b) can come into contact with the outlet port (9) when the screw rotors (3) are rotated, The connection is such that a flow from the second compression chamber (11b) to the first compression chamber (11a) is possible so that the pressure in the second compression chamber (11b) is reduced, the connection not being directly connected to the outlet port (9).
    [2]
    Oil-injected screw-type vacuum pump element according to claim 1, characterized in that the first compression chamber (11a) contacts the inlet port (9) and the outlet head face (6).
    [3]
    Oil-injected vacuum pump element according to claim 1 or 2, characterized in that the aforementioned connection is realized by means of a groove (13) arranged in the outlet head face (6), said groove (13) extending from the first compression chamber (11a) up to the second compression chamber (11b).
    [4]
    Air-injected vacuum pump element according to claim 3, characterized in that the groove (13) comprises at least one slot-shaped straight or curved portion (15).
    [5]
    Oil-injected vacuum pump element according to claim 4, characterized in that, adjacent to said slot-shaped portion (15), the groove (13) comprises a widening portion (16) with which the groove (13) at least partially overlaps with the first compression chamber (11a) ).
    [6]
    Oil-injected vacuum pump element according to claim 1 or 2, characterized in that the aforementioned connection is realized by means of a groove part in the outlet head face (6) which at least partially overlaps with the second compression chamber (11b) and a channel or line connecting thereto leads to the first compression chamber (11a), with this channel or line being built in or not in the housing. Oil-injected vacuum pump element according to one of the preceding claims, characterized in that the minimum cross section in mm2 of the connection is between 0.01 and 0.1 times the maximum volumetric flow rate of the element (1) in liters per second, at preferably between 0.01 and 0.08 times, more preferably between 0.01 and 0.06 times, and more preferably between 0.01 and 0.04 times.
    [8]
    Oil-injected vacuum pump element according to one of the preceding claims, characterized in that the end (14b) of the connection in communication with the second compression chamber (11b) on the outlet head face (6) is designed such that the maximum contact surface between the connection and said second compression chamber (11b) has a surface area in mm 2 between 0.01 and 0.1 times the maximum volumetric flow rate of the element in liters per second, preferably between 0.01 and 0.08 times, more preferably between 0.01 and 0.06 times and more preferably between 0.01 and 0.04 times.
    [9]
    Oil-injected vacuum pump element according to one of the preceding claims, characterized in that the overlap between the connection and the first compression chamber (11a) is such that the connection between the first compression chamber (11a) and the second compression chamber (11b) is maintained at rotation of the screw rotors (3) until the volume of the second compression chamber (11b) goes to zero or substantially to zero.
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    同族专利:
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    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    WO1989012752A1|1988-06-17|1989-12-28|Svenska Rotor Maskiner Ab|Rotary positive displacement compressor and refrigeration plant|
    WO2006095364A1|2005-02-02|2006-09-14|Elgi Equipmetns Ltd|A system and a method for capacity control in a screw compressor|
    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    US201562103772P| true| 2015-01-15|2015-01-15|
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    BR112017014897-8A| BR112017014897A2|2015-01-15|2016-01-07|oil-injected vacuum pump element|
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