WO2023179954A1

WO2023179954A1 - Vacuum pump

Info

Publication number: WO2023179954A1
Application number: PCT/EP2023/052896
Authority: WO
Inventors: Paul DECORDE
Original assignee: Pfeiffer Vacuum
Priority date: 2022-03-21
Filing date: 2023-02-07
Publication date: 2023-09-28
Also published as: FR3133650A1; FR3133650B1

Abstract

The invention relates to a vacuum pump (1) comprising: a stator (2) comprising at least one pumping stage (T1-T5); two shafts (4) carrying rotors (5) which is configured to rotate in the pumping stage (T1-T5) about an axis of rotation (l-l) in each case; at least one oil sump (6) comprising a chamber which is configured to contain a liquid lubricant intended to lubricate elements (10, 11) allowing the rotation of the shafts (4); and a device (12) for determining the level of liquid lubricant configured to determine information which is representative of the level of liquid lubricant contained in the chamber of the oil sump (6) from the differential pressure measurement between the pressure exerted by the liquid lubricant and the gas pressure prevailing in the volume of the chamber of the oil sump (6) above the level of oil lubricant.

Description

Description Title of the invention: Vacuum pump

Technical field of the invention

The present invention relates to a vacuum pump and more particularly, to a device for determining the level of liquid lubricant contained in a chamber of the oil sump of a dry vacuum pump.

Technical background

[0002] Dry vacuum pumps comprise one or more pumping stages in series in which a gas to be pumped circulates between suction and discharge. Among the known vacuum pumps, we distinguish those with rotating lobes, also known under the name “Roots”, or those with a nozzle, also known under the name “Claw”, or those with a screw. These vacuum pumps are called “dry” because in operation, the rotors rotate inside the stator without any mechanical contact between them or with the stator, which allows no oil to be used in the pumping stages.

[0003] The rotors are supported by bearings lubricated by oil or grease and they are synchronized by means of gears also lubricated. It is essential that no traces of oil or grease are found in the pumping part for so-called “dry” applications, such as semiconductor substrate manufacturing processes. A sealing means through which the shafts are still capable of rotating, isolates the area containing lubricants from the dry pumping part.

[0004] An oil agitator, such as a stirrer disk, is generally used to create a cloudy atmosphere of air and lubricants in the oil pan, facilitating lubrication of the bearings. The oil agitator is attached to one of the pump shafts, with one lower end dipping into the liquid oil. The rotation of the shaft supporting the agitator forms an oil mist, projecting droplets of lubricant onto the walls of the housing which then trickle down to the components to be lubricated.

[0005] It is very important to monitor the oil level to ensure that the components of the vacuum pump are properly lubricated.

[0006] For this, oil pans generally include a transparent window through which users can check the presence and level of oil. The disadvantage is that the user must go on site to carry out the visual examination. Additionally, it may be necessary to remove the vacuum pump cover to access the sight glass if special covers have not been designed. By Elsewhere, after some time of use, the window may become dull, making it difficult to see the oil level.

[0007] There are also dedicated sensors for measuring the oil level, such as float sensors or electronic sensors, capacitive type. However, the swirls caused by the oil agitator can interfere with the correct measurement of the oil level using conventional floats. Furthermore, we note that electronic sensors may not always function correctly or lack robustness or precision because the oil level variations to be monitored are small and therefore difficult to detect with low-cost sensors.

Summary of the invention

[0008] An aim of the present invention is to propose a vacuum pump resolving at least one of the drawbacks described above, making it possible in particular to monitor the oil level using a sufficiently precise, inexpensive and robust device.

[0009] For this purpose, the invention relates to a vacuum pump comprising:

- a stator comprising at least one pumping stage,

- two shafts carrying rotors configured to rotate in the pumping stage around a respective axis of rotation, and

- at least one oil pan comprising a chamber configured to contain a liquid lubricant intended to lubricate elements allowing the rotation of the shafts, characterized in that the vacuum pump further comprises a device for determining the level of liquid lubricant configured to determine information representative of the level of liquid lubricant contained in the oil sump chamber from the pressure differential measurement between the pressure exerted by the liquid lubricant and the gas pressure prevailing in the volume of the oil sump chamber above the oil lubricant level.

[0010] Thus, in operation, the level of liquid lubricant contained in the chamber of the oil pan can be determined by the measurement of pressure exerted by this height of lubricant from which the measurement of gas pressure (mostly of air) above the lubricant level. Indeed, although the atmosphere of the oil casings of the vacuum pump is not placed under vacuum but left at atmospheric pressure, it is also subject to a lesser extent, the pressure variations taking place in the pumping part . In fact, the sealing devices, which are relatively effective with respect to lubricants, are not perfectly gas-tight since they must allow the rotation of the shafts. When the gas pressure is higher in the pumping stage next to the oil sump than in the oil sump, for example when starting pumping from the atmospheric pressure, the pumped gases can seep into the oil pan and increase the gas pressure above the liquid level. Also when the gas pressure is lower in the pumping stage next to the oil sump than in the oil sump, the gas pressure of the oil sump can be lowered by suction through the suction devices. sealing of shaft passages. By taking into account the measurement of the gas pressure above the liquid level, we avoid measurement fluctuations due to variations in gas pressure. We can then determine the height of the liquid lubricant by measuring the pressure exerted by the liquid independently of variations in gas pressure.

[0011] Furthermore, the differential measurement of the device for determining the level of liquid lubricant depends only on the height of liquid contained in the volume above the pressure measurement point, whatever the shape of the volume of the chamber. of the oil pan. It is then possible to adapt the shape of the oil pan chamber to favor measurement accuracy at a certain liquid lubricant height level.

[0012] The vacuum pump may also include one or more of the characteristics which are described below, taken alone or in combination.

[0013] According to an exemplary embodiment, the device for determining the level of liquid lubricant comprises:

- a first pressure sensor configured to measure the pressure exerted by the liquid lubricant contained in the oil pan chamber,

- a second pressure sensor configured to measure the gas pressure prevailing in the volume of the oil pan chamber above the oil lubricant level.

[0014] The vacuum pump may include a processing unit comprising for example a controller or microcontroller or microprocessor or computer or logic circuit.

[0015] The processing unit can be configured to receive the output signals from the pressure sensors and to deduce information representative of the level of liquid lubricant contained in the chamber of the oil pan from the differential measurement of the signals pressure sensor output.

According to another embodiment, the device for determining the level of liquid lubricant comprises a differential pressure sensor.

The first and/or the second pressure sensor or the differential pressure sensor is for example a piezoelectric sensor. [0018] The pressure measurement taken by the liquid lubricant contained in the oil pan chamber is preferably located in the bottom of the oil pan chamber.

The processing unit can be configured to average the information representative of the liquid level over a predetermined duration.

The vacuum pump may include a temperature sensor connected to the processing unit, the processing unit being configured to determine information representative of the level of liquid lubricant taking into account the measured temperature.

According to an exemplary embodiment, the volume of the oil pan chamber has a straight vertical shape of constant horizontal section.

According to an exemplary embodiment, the volume of the oil pan chamber has a straight vertical shape with a horizontal section expanding upwards. According to an exemplary embodiment, the volume of the oil pan chamber has a straight vertical shape with a horizontal section thinning towards the top. According to an exemplary embodiment, the volume of the oil pan chamber is formed by a lower part and an upper part, the lower part having a constant horizontal section narrower than an upper part.

[0025] The width of the horizontal section of the lower part is for example less than 3cm, for example less than 1cm or around 10mm. Brief description of the figures

[0026] Other advantages and characteristics will appear on reading the following description of a particular embodiment of the invention, but in no way limiting, as well as the appended drawings in which:

[0027] [Fig. 1] Figure 1 is a schematic representation of an example of a vacuum pump.

[0028] [Fig. 2A] Figure 2A illustrates a first example of the shape of the oil pan chamber.

[0029] [Fig. 2B] Figure 2B is a graph showing, for the first embodiment of Figure 2A, as a function of the height of oil H contained in the chamber (on the abscissa, in cm) on the one hand, in solid lines, the pressure P exerted by the height of oil (right ordinate, in bar) and on the other hand, in broken lines, the quantity of oil Q contained in the chamber (left ordinate, in ml).

[0030] [Fig. 3A] Figure 3A illustrates a second example of the shape of the oil pan chamber. [0031] [Fig. 3B] Figure 3B is a graph showing, for the second embodiment of Figure 3A, as a function of the height of oil H contained in the chamber (on the abscissa, in cm) on the one hand, in solid lines, the pressure P exerted by the height of oil (right ordinate, in bar) and on the other hand, in broken lines, the quantity of oil Q contained in the chamber (left ordinate, in ml).

[0032] [Fig. 4A] Figure 4A illustrates a third example of the shape of the oil pan chamber.

[0033] [Fig. 4B] Figure 4B is a graph showing, for the third embodiment of Figure 4A, as a function of the height of oil H contained in the chamber (on the abscissa, in cm) on the one hand, in solid lines, the pressure P exerted by the height of oil (right ordinate, in bar) and on the other hand, in broken lines, the quantity of oil Q contained in the chamber (left ordinate, in ml).

[0034] [Fig. 5A] Figure 5A illustrates a fourth example of the shape of the oil pan chamber.

[0035] [Fig. 5B] Figure 5B is a graph showing, for the fourth embodiment of Figure 5A, as a function of the height of oil H contained in the chamber (on the abscissa, in cm) on the one hand, in solid lines, the pressure P exerted by the height of oil (right ordinate, in bar) and on the other hand, in broken lines, the quantity of oil Q contained in the chamber (left ordinate, in ml).

[0036] In these figures, identical elements bear the same reference numbers.

detailed description

[0037] The following achievements are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features only apply to a single embodiment. Single features of different embodiments may also be combined or interchanged to provide other embodiments.

[0038] A primary vacuum pump is defined as a volumetric vacuum pump, which is configured to suck up, transfer, then discharge a gas to be pumped at atmospheric pressure or beyond. The rotors of the primary vacuum pump can be Roots, Claw or screw type. The rotors are carried by two shafts rotated by a primary vacuum pump motor. A primary vacuum pump is also configured to be able to be started at atmospheric pressure.

[0039] Roots vacuum pump (also called “Roots Blower” in English or Roots compressor or “Booster” in English) is defined as a vacuum pump. volumetric configured to, using two Roots rotors, suck up, transfer and then discharge a gas to be pumped. The Roots vacuum pump is mounted upstream and in series with a primary vacuum pump. The rotors are carried by two shafts rotated by a Roots vacuum pump motor.

By “upstream” is meant an element which is placed before another with respect to the direction of circulation of the pumped gases F. Conversely, by “downstream” is meant an element placed after another with respect to the direction of circulation of the pumped gases F. The arrows F in Figure 1 show the direction of circulation of the pumped gases. The invention applies to any type of dry vacuum pump, that is to say comprising one or at least two pumping stages, such as comprising one to ten pumping stages. This vacuum pump can be a primary vacuum pump comprising a plurality of pumping stages and configured to discharge the pumped gases at atmospheric pressure or a vacuum pump, called Roots or Roots compressor, of one to three pumping stages which use, is connected in series and upstream of a primary vacuum pump and whose discharge pressure is that obtained by the primary vacuum pump.

The vacuum pump 1 comprises a stator 2 comprising at least one pumping stage T1-T5, two shafts 4 (only one is shown on the vacuum pump in Figure 1) carrying rotors 5 configured to rotate in the pumping stage T 1 -T5 around a respective axis of rotation l-l, and at least one oil sump 6 comprising a chamber configured to contain a liquid lubricant intended to lubricate elements 10, 11 allowing the rotation of the shafts 4 .

The vacuum pump 1 comprises for example two oil sumps 6 arranged on either side of at least one pumping stage.

The vacuum pump 1 also includes at least one lubricant sealing device 7 interposed between the oil sump 6 and a pumping stage at each shaft passage. The sealing device 7 may comprise at least one annular seal, for example a “dynamic” seal, that is to say non-rubbing, such as a segment seal, a labyrinth or “wall” seal. gas, or a rubbing annular seal, such as a lip seal or a combination of these embodiments. The sealing device 7 creates a very low conductance around the rotating shafts 4, which makes it possible to strongly limit the passage of lubricating fluids from the oil sump 6 to the dry pumping stages T 1 -T5 and vice versa while by allowing the shafts 4 to rotate.

The vacuum pump 1 comprises for example several pumping stages T1 -T5, such as five, connected in series between an inlet 8 and an outlet 9 of the vacuum pump 1. The pumping stages T1, T5 adjoining the sealing devices 7 are here the first and the last pumping stage.

[0046] Each pumping stage T1-T5 comprises a respective input and an output. When the vacuum pump 1 has several pumping stages, the successive pumping stages are connected in series one after the other by respective inter-stage channels connecting the output of the preceding pumping stage to the inlet of the next floor. The pumping flow rates of the pumping stages T1-T5 are decreasing or equal with their position between the inlet and the outlet of the vacuum pump, the flow rate generated by the first pumping stage T 1 at the lowest pressure corresponding to the flow rate of greatest pumping.

The rotors 5 are rotated by at least one motor M of the vacuum pump 1. During rotation, the gas sucked in from the inlet is trapped in the volume generated by the rotors 5 and the stator 2, then is driven by the rotors 5 towards the next stage. The rotors 5 of the vacuum pump 1 have for example lobes of identical profiles, for example of the "Roots" type (section in the shape of an "eight" or "bean") or of the "Claw" type or are of the screw or another similar principle of positive displacement vacuum pump.

[0048] The shafts 4 carrying the rotors 5 are guided in rotation in bearings lubricated by a liquid lubricant, such as oil, contained in the oil pan 6. [0049] In operation, the liquid lubricant lubricates the elements allowing the rotation of the shafts 4, in particular the ball bearings 10 of the bearings and the synchronization gears 11 allowing the synchronized rotation of the shafts 4. [0050] The vacuum pump 1 further comprises a device for determining the lubricant level liquid 12 configured to determine information representative of the level of liquid lubricant contained in the chamber of the oil pan 6 from the pressure differential measurement between the pressure exerted by the liquid lubricant and the gas pressure prevailing in the volume of the chamber of the oil pan 6 above the oil lubricant level.

[0051] According to a first exemplary embodiment, the device for determining the level of liquid lubricant 12 comprises a first pressure sensor 13 and a second pressure sensor 14. The first pressure sensor 13 is configured to measure the pressure exerted by the liquid lubricant contained in the oil pan chamber 6. The second pressure sensor 14 is configured to measure the gas pressure prevailing in the volume of the oil pan chamber 6 above the oil lubricant level. The vacuum pump 1 comprises for example a processing unit 15 comprising for example a controller or microcontroller or microprocessor or computer or logic circuit. The processing unit 15 can be configured to receive the output signals from the pressure sensors 13, 14 and to deduce information representative of the level of liquid lubricant contained in the chamber of the oil pan 6 from the differential measurement output signals from the pressure sensors 13, 14.

According to another embodiment, the device for determining the level of liquid lubricant 12 comprises a differential pressure sensor. The differential pressure sensor is configured to directly deliver a differential measurement signal between the pressure exerted by the liquid lubricant contained in the chamber of the oil pan 6 and the gas pressure prevailing in the volume of the chamber of the oil pan 6 above the oil lubricant level.

The first and/or the second pressure sensor 13, 14 or the differential pressure sensor is for example a piezoelectric sensor. Piezoelectric sensors are very robust, particularly over time, in the face of shocks or attacks from corrosive gases. In addition, they are relatively inexpensive.

[0055] The pressure measurement exerted by the liquid lubricant contained in the chamber of the oil pan 6, carried out either by the first pressure sensor 13 or by the differential pressure sensor, is preferably located in the bottom of the oil pan chamber 6. The device for determining the level of liquid lubricant 12 can thus measure the greatest height of liquid lubricant accessible and therefore have better sensitivity.

[0056] According to an exemplary embodiment, the processing unit 15 can be configured to average the information representative of the liquid level, or of the output signals of the pressure sensors 13, 14 or of the differential pressure sensor, over a predetermined duration, for example between one and ten minutes or every 24 hours. Averaging these signals makes it possible to avoid the turbulence that could be caused by the oil agitator.

[0057] According to an exemplary embodiment, the vacuum pump 1 comprises a temperature sensor 16 configured to measure the temperature of the vacuum pump 1, for example at the stator 2 or the oil sump 6. This temperature sensor temperature 16 is for example that used for temperature regulation of the vacuum pump 1. It is connected to the processing unit 15, the processing unit 15 being configured to determine information representative of the level of liquid lubricant taking into account the measured temperature. We can thus correct the effects of thermal expansion of the volume of the oil pan chamber 6 or liquid lubricant from the temperature measurement.

[0058] Thus, in operation, the level of liquid lubricant contained in the chamber of the oil pan 6 can be determined by the measurement of pressure exerted by this height of lubricant from which the measurement of gas pressure (mainly d 'air) above the lubricant level. Indeed, although the atmosphere of the oil casings 6 of the vacuum pump 1 is not placed under vacuum but left at atmospheric pressure, this is also subject to a lesser extent, the pressure variations taking place in the pumping part. In fact, the sealing devices 7, which are relatively effective with respect to lubricants, are not perfectly gas-tight since they must allow the rotation of the shafts 4. When the gas pressure is higher in the pumping stage located next to the oil pan 6 than in the oil pan 6, for example when starting pumping from atmospheric pressure, the pumped gases can infiltrate into the oil pan 6 and increase the gas pressure at above the liquid level. Also when the gas pressure is lower in the pumping stage located next to the oil pan 6 than in the oil pan 6, the gas pressure of the oil pan 6 can be lowered by suction through the sealing devices 7 of the shaft passages. By taking into account the measurement of the gas pressure above the oil level, we avoid measurement fluctuations due to variations in gas pressure. We can then determine the height of the liquid lubricant by measuring the pressure exerted by the liquid independently of variations in gas pressure.

[0059] Furthermore, the differential measurement of the device for determining the level of liquid lubricant 12 depends only on the height of liquid contained in the volume above the pressure measurement point, whatever the shape of the volume of the chamber of the oil pan 6. It is then possible to adapt the shape of the chamber of the oil pan 6 to favor measurement precision at a certain height level of liquid lubricant.

[0060] Figures 2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B thus show four examples of chamber shapes for the same total volume of maximum capacity of liquid lubricant (here oil), here 400ml.

[0061] According to a first embodiment, the volume of the chamber of the oil pan 6 has a straight vertical shape of constant horizontal section, such as cylindrical or parallelepiped (Figure 2A). [0062] According to a second embodiment, the volume of the chamber of the oil pan 6 has a straight vertical shape of horizontal section expanding upwards, such as a truncated cone (Figure 3A).

[0063] According to a third embodiment, the volume of the chamber of the oil pan 6 has a straight vertical shape of horizontal section thinning upwards, such as a truncated cone, inverted relative to Figure 3A (Figure 4A).

According to a fourth embodiment, the volume of the chamber of the oil pan 6 is formed by a lower part and an upper part, the lower part having a constant horizontal section narrower than an upper part (Figure 5A ). The width of the horizontal section of the lower part depends on the precision sought, it is for example less than 3cm, for example less than 1cm or around 10mm.

[0065] In all cases, the variation in pressure due to the variation in height of liquid lubricant contained in the chamber (continuous lines in Figures 2B, 3B, 4B, 5B) is proportional to the height of the liquid lubricant. We also see that the pressure variation is independent of the shape of the chamber.

[0066] In the first example for which the volume of the chamber of the oil pan 6 has a straight vertical shape of constant horizontal section (FIG. 2A), the quantity of oil contained in the chamber changes proportionally with the height of the liquid. (dashed lines in Figure 2B). The measurement accuracy is therefore the same for small and large quantities of liquid lubricant. In this example, a pressure variation of 1 mbar (100Pa) corresponds to an increase of 2mm in oil height and 100ml in oil quantity and this over the entire oil height, that is to say here for oil heights between 0mm and 8mm.

[0067] In the second embodiment for which the volume of the chamber of the oil pan 6 has a straight vertical shape of horizontal section increasing upwards (FIG. 3A), the quantity of oil contained in the chamber first evolves slowly for small oil heights then quickly for large oil heights (dashed lines in Figure 3B). For example, a pressure variation of 1 mbar, or 2mm of oil height, corresponds to 50ml of oil quantity for oil heights between 0mm and 2mm while it corresponds to 200ml of oil quantity for oil heights between 6mm and 8mm. In other words, the same variation in quantity of liquid lubricant produces a greater variation in height of lubricant and therefore in pressure when the chamber contains little liquid lubricant than when it contains large quantities. quantities. The pressure measurement is therefore more precise for small levels of liquid lubricant, that is to say when the chamber of the oil pan 6 is lightly filled. [0068] In the third embodiment for which the volume of the chamber of the oil pan 6 has a straight vertical shape of horizontal section thinning upwards (FIG. 4A), the quantity of oil contained in the chamber conversely evolves quickly for small oil heights then slowly for large oil heights (dashed lines in Figure 4B). For example, a pressure variation of 1 mbar, or 2mm of oil height, corresponds to 200ml of oil quantity for oil heights between 0mm and 2mm while it corresponds to 28.5ml of quantity of oil. oil for oil heights between 6mm and 8mm. In other words, the same variation in quantity of liquid lubricant produces a greater variation in height of lubricant and therefore in pressure when the chamber contains a lot of liquid lubricant than when it contains little. The pressure measurement is therefore more precise for high levels of liquid lubricant, that is to say when the chamber of the oil pan 6 is well filled. [0069] In the fourth embodiment for which the volume of the chamber of the oil pan 6 is formed by a lower part and an upper part, the lower part having a constant horizontal section narrower than an upper part (figure 5A), the quantity of oil contained in the chamber first evolves along a gentle slope when the oil is contained in the lower part then along a steep slope when the height of oil evolves in the upper part (dashed lines on Figure 5B). For example, a pressure variation of 1 mbar, or 2mm of oil height, corresponds to 50ml of oil quantity for oil heights between 0mm and 2mm while it corresponds to 150ml of oil quantity for oil heights between 6 and 8mm. In other words, a quantity of liquid lubricant between 0ml and 100ml in the lower part generates a pressure variation of 2mbar (200Pa) while a pressure variation of 2mbar is generated by a quantity of liquid lubricant between 100ml and 400ml, beyond the lower part. The pressure measurement is therefore more precise for small levels of liquid lubricant, that is to say when the oil height does not exceed the lower part. The presence of a small quantity of lubricant can therefore easily be detected, which can make it possible to know whether the oil pan 6 is empty or not, for example to prevent the vacuum pump 1 from starting in the event of non-filling. of the oil pan 6. Then, when the quantity of oil exceeds the lower part, the liquid lubricant level determination device 12 allows quantitative measurement of the liquid lubricant level.

Claims

[Claim 1] Vacuum pump (1) comprising:

- a stator (2) comprising at least one pumping stage (T1-T5),

- two shafts (4) carrying rotors (5) configured to rotate in the pumping stage (T1 -T5) around a respective axis of rotation (l-l), and

- at least one oil pan (6) comprising a chamber configured to contain a liquid lubricant intended to lubricate elements (10, 11) allowing the rotation of the shafts (4), characterized in that the vacuum pump (1) further comprises a device for determining the level of liquid lubricant (12) configured to determine information representative of the level of liquid lubricant contained in the chamber of the oil pan (6) from the pressure differential measurement between the pressure exerted by the liquid lubricant and the gas pressure prevailing in the volume of the oil pan chamber (6) above the oil lubricant level.

[Claim 2] Vacuum pump (1) according to the preceding claim, characterized in that the device for determining the level of liquid lubricant (12) comprises:

- a first pressure sensor (13) configured to measure the pressure exerted by the liquid lubricant contained in the chamber of the oil pan (6),

- a second pressure sensor (14) configured to measure the gas pressure prevailing in the volume of the oil pan chamber (6) above the oil lubricant level.

[Claim 3] Vacuum pump (1) according to claim 1, characterized in that the device for determining the level of liquid lubricant (12) comprises a differential pressure sensor.

[Claim 4] Vacuum pump (1) according to one of claims 2 or 3, characterized in that the first and/or the second pressure sensor (13, 14) or the differential pressure sensor is a piezoelectric sensor.

[Claim 5] Vacuum pump (1) according to one of the preceding claims, characterized in that the pressure measurement taken by the liquid lubricant contained in the chamber of the oil pan is located in the bottom of the chamber of the oil pan (6).

[Claim 6] Vacuum pump (1) according to one of the preceding claims, characterized in that it comprises a processing unit (15) configured to average the information representative of the liquid level over a predetermined duration.

[Claim 7] Vacuum pump (1) according to one of the preceding claims, characterized in that it comprises a processing unit (15) and a temperature sensor (16) connected to the processing unit (15) , the processing unit (15) being configured to determine information representative of the level of liquid lubricant taking into account the measured temperature.

[Claim 8] Vacuum pump (1) according to one of the preceding claims, characterized in that the volume of the chamber of the oil sump (6) has a straight vertical shape of constant horizontal section.

[Claim 9] Vacuum pump (1) according to one of claims 1 to 7, characterized in that the volume of the chamber of the oil sump (6) has a straight vertical shape of horizontal section increasing towards the high.

[Claim 10] Vacuum pump (1) according to one of claims 1 to 7, characterized in that the volume of the chamber of the oil sump (6) has a straight vertical shape of horizontal section thinning towards the high.

[Claim 11] Vacuum pump (1) according to one of claims 1 to 7, characterized in that the volume of the chamber of the oil sump (6) is formed by a lower part and an upper part, the part lower having a constant horizontal section narrower than an upper part.

[Claim 12] Vacuum pump (1) according to the preceding claim, characterized in that the width of the horizontal section of the lower part is less than 3cm.