CN112805472A

CN112805472A - Method for controlling the temperature of a vacuum pump, and associated vacuum pump and apparatus

Info

Publication number: CN112805472A
Application number: CN201980066007.4A
Authority: CN
Inventors: Y·格勒尼耶; P·德科尔德
Original assignee: Pfeiffer Vacuum SAS
Current assignee: Pfeiffer Vacuum SAS
Priority date: 2018-10-17
Filing date: 2019-09-26
Publication date: 2021-05-14
Anticipated expiration: 2039-09-26
Also published as: FR3087504A1; FR3087504B1; EP3867531B1; KR20210074368A; US20210404476A1; JP2022505202A; CN112805472B; WO2020078689A1; TW202018186A; EP3867531A1; TWI798487B

Abstract

The invention relates to a method for controlling the temperature of a vacuum pump (2) of the dry vacuum pump type subjected to variable pumping loads, wherein the temperature of the vacuum pump (2) is controlled by means of at least one cooling element (11a, 11b) coupled to the stator (5) as a function of a temperature setpoint and of a temperature measurement of the stator (5), characterized in that it is monitored whether a value of a parameter indicative of the pumping load and selected from the current or power consumed by the vacuum pump (2) is below a load threshold value, and the temperature setpoint is increased if the value of the parameter indicative of the pumping load is below the load threshold value. The invention also relates to a vacuum pump of the dry vacuum pump type and to an apparatus.

Description

Method for controlling the temperature of a vacuum pump, and associated vacuum pump and apparatus

Technical Field

The present invention relates to a method for controlling the temperature of a vacuum pump of the dry vacuum pump type. The invention also relates to a vacuum pump of the dry vacuum pump type, comprising means for carrying out said control method. The invention also relates to an apparatus comprising said vacuum pump.

Background

A rough vacuum pump of the dry vacuum pump type comprises several pumping stages in series, through which the gas to be pumped circulates between an intake and an output. There are differences between known rough vacuum pumps, namely pumps with rotating lobes (also known as "roots" pumps), pumps with two or more lobes (known as "claw" pumps), and screw pumps. Vacuum pumps of the roots compressor (or more commonly "roots blower") type are also known, having one or two stages, and are used upstream of rough vacuum pumps in order to increase the pumping capacity under conditions of very high flow rates.

These vacuum pumps are called "dry" because in operation there is no mechanical contact between the rotors rotating inside the stator or with the stator, which makes it possible to not use oil (lubricating oil) in the pumping stages.

More and more applications require the possibility of significantly and rapidly varying the gas flow to be pumped between a process step, on the one hand, in which the vacuum pump is required to circulate a high flow of gas, in the order of several slm (standard liters per minute) or tens of slm, and an idle (or standby) step, on the other hand, in which the vacuum pump is operated at a so-called "ultimate vacuum pressure" and the gas flow to be pumped is zero or very low.

Pumping high flows of gas causes the vacuum pump to heat up significantly due to compression. The increase in temperature makes it possible to avoid condensation or solidification of contaminating gaseous substances into powder in the vacuum pump. However, it is necessary to cool the bearings of the vacuum pump to avoid any failure. Furthermore, in some applications it is desirable to control the stator temperature so that it does not exceed a predetermined maximum value beyond which pumped gaseous matter may accumulate in the pump and cause the pump to seize.

Cooling of the stator is typically achieved by circulating water at ambient temperature through a cooling circuit in thermal contact with the stator.

However, in the above case, the flow rate of the gas to be pumped drops sharply, the vacuum pump does not heat itself, and may cool down sharply. The stator in contact with the cooling circuit then undergoes a temperature drop, while the rotor, which is not directly cooled, remains at a high temperature.

The temperature difference between the rotor and the stator may be exacerbated by the fact that: the measurement point for controlling the temperature of the cooling circuit is not necessarily located at a suitable position that allows detection of rapid temperature changes due to pumping load changes. Thus, the measured temperature may be overestimated and result in a continuous command to cool the stator even if, for example, the temperature at the bearings has dropped significantly. The response time required to actually identify a stator temperature drop may be relatively long, which may result in an expanded difference between temperatures.

Such temperature differences may lead to a loss of clearance, in particular axial clearance, between the stator and the rotor due to various thermo-mechanical behaviors, since cooling circuits are usually arranged at each axial end of the vacuum pump in the region of the bearings, and may lead to a reduction of the inter-shaft distance due to the shaft support shrinkage. These clearance losses can result in the pump jamming or the rotors coming into contact with each other.

Disclosure of Invention

It is an object of the present invention to propose a vacuum pump of the dry vacuum pump type and a method for controlling the temperature of the vacuum pump, which are able to solve at least one of the above drawbacks, in particular by limiting the clearance losses and seizing.

To this end, one subject of the invention is a method for controlling the temperature of a vacuum pump of the dry vacuum pump type subjected to variable pumping loads, said vacuum pump comprising:

-a stator,

-at least one pumping stage, the pumping stages,

two shafts extending into the at least one pumping stage and each carrying at least one rotor configured to rotate synchronously in opposite directions in the stator to drive gas to be pumped from the suction inlet to the output of the vacuum pump,

-at least one cooling element coupled with the stator,

-at least one temperature sensor configured to measure the temperature of the stator, an

A control unit configured to control the temperature of the stator by means of the at least one cooling element and the at least one temperature sensor,

wherein the temperature of the vacuum pump is controlled by means of the at least one cooling element coupled with the stator in dependence on a temperature setpoint and a measured value of the temperature of the stator,

characterised in that the current or power consumed by the vacuum pump is monitored and the value of a parameter indicative of (characteristic of) the pumping load is below a load threshold, and the temperature set point is raised (increased) if the value of the parameter indicative of the pumping load is below the load threshold.

Thus, the change in the temperature set point makes it possible to cut off the cooling of the stator more quickly by the cooling element, so that the stator heats up in the vicinity of the cooling element. Raising the temperature set point during low pumping load phases keeps the stator as hot as during high load phases, so that the risk of jamming or rotor contact with each other can be limited.

Maintaining this higher temperature during the low load phase also avoids the formation of cold zones where condensable contaminants may freeze or condense.

The change in temperature set point triggered by monitoring the pumping load also makes the method highly responsive.

By incorporating the thermal behavior of the vacuum pump into the determination of the temperature control, the monitoring can be performed based on the information already provided by the sensors of the vacuum pump, without adding additional temperature sensors, without providing information about the process being performed in the chamber, and without changing the position of at least one temperature sensor or the structure of the cooling element.

The temperature control method may also include one or more of the features described below, which may be considered alone or in combination.

According to an exemplary embodiment, the temperature setpoint is increased for at least controlling the temperature by a cooling element coupled with a pumping stage of the vacuum pump, referred to as a low pressure pumping stage.

According to an exemplary embodiment, after the temperature set point has been increased, it is monitored whether the value of the parameter indicative of the pumping load is above a load threshold, and if the value of the parameter indicative of the pumping load is above the load threshold, the increased temperature set point is maintained for a predetermined additional length of time.

The predetermined additional length of time is, for example, greater than 10 minutes.

The rise in the temperature set point (rise value) is, for example, greater than 3 ℃.

The rise in temperature set point is, for example, less than 20 ℃.

Another subject of the invention is a vacuum pump of the dry vacuum pump type, comprising:

-a stator,

-at least one pumping stage, the pumping stages,

-at least one cooling element coupled with the stator,

characterized in that the control unit is configured to perform the temperature control method as described above.

The vacuum pump of the dry vacuum pump type may be a multi-stage rough vacuum pump, i.e. a pump comprising at least two pumping stages mounted in series. The vacuum pump may be a roots blower type vacuum pump which again comprises one or two pumping stages mounted in series.

According to an exemplary embodiment, a vacuum pump of the dry vacuum pump type comprises two cooling elements coupled to the stator, one cooling element being arranged at each axial end of the vacuum pump.

Another subject of the invention is an apparatus comprising a chamber, characterized in that it comprises a vacuum pump of the dry vacuum pump type as described above, connected to the chamber for pumping therein.

Drawings

Further characteristics and advantages of the invention will become apparent from the following description, given by way of non-limiting example and made with reference to the accompanying drawings, in which:

fig. 1 shows a schematic view of an apparatus according to the invention.

Fig. 2 shows a schematic view, partly in section and partially in disassembled condition, of the vacuum pump of the apparatus of fig. 1, showing only the elements necessary for operation.

Fig. 3 is a schematic diagram illustrating various steps of a temperature control method for the vacuum pump of fig. 2.

Fig. 4 is a graph showing an example of a curve obtained as a function of time (in minutes) for:

the power consumed by the vacuum pump of figure 2 (in watts, vertical axis on the right side) (curve a),

stator temperature (in ° c, vertical axis on the left side) measured by vacuum pump temperature sensor (curve B), and

stator temperatures measured in an indicative manner by two test temperature sensors fixed in the center of the vacuum pump cooling element (curves C and D).

In these figures, like elements have like reference numerals. The following embodiments are merely examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference to the same embodiment or feature applies to only a single embodiment. Simple features of the various embodiments may also be combined or interchanged to provide further embodiments.

Detailed Description

Fig. 1 shows a first example of an apparatus 1 comprising a vacuum pump 2 of the dry vacuum pump type and a chamber 3, the vacuum pump 2 being connected to the chamber 3, for example by a valve 4, for pumping in the chamber 3.

During a step called "process" steps P1, P2 (fig. 3), a large amount of gas flow, for example periodically, of the order of some slm or some tens of slm, may be introduced into chamber 3. These process steps P1, P2 may be performed before and after a step called "idle" step I, in which the introduced gas flow is low or zero. During the idle step I, the vacuum pump 2 is operated at the so-called "ultimate vacuum pressure", for example for a period of time exceeding a few minutes, so that the chamber 3 is cleaned. This series of steps occurs, for example, in the process of manufacturing semiconductors, such as the process known as the "HarpXT" flow.

As best shown in fig. 1 and 2, the vacuum pump 2 comprises a stator 5, at least one pumping stage T1-T5, two shafts 6, 7 extending into said at least one pumping stage T1-T5 and carrying at least one rotor 8, respectively, at least one

cooling element

11a, 11b coupled with the stator 5, at least one

temperature sensor

12a, 12b configured to measure the temperature of the stator 5, and a control unit 13 configured to control the temperature of the stator 5 through said at least one

cooling element

11a, 11b and said at least one

temperature sensor

12a, 12 b.

The rotors 8 are configured to rotate synchronously in opposite directions in the stator 5 to drive gas G to be pumped from the suction inlet 9 of the vacuum pump 2 to the output 10 of the pump 2.

The rotor 8 has, for example, lobes of the same profile, for example of the "roots" type (cross-sectional shape "8" or "kidney bean") or of the "claw" type. According to another example, the pump rotor 8 is of the "screw" type.

The vacuum pump 2 comprises, for example, at least two pumping stages, for example five pumping stages. Each pumping stage T1-T5 includes an inlet and an outlet, respectively. Successive pumping stages T1-T5 are connected in series by respective inter-stage conduits 14 connecting the outlet (or output) of a preceding pumping stage to the inlet (or suction) of the next stage.

During rotation, the gas drawn in from the inlet is trapped in the volume created by the rotor 8 and then driven by the rotor 8 towards the output 10 (the direction of gas circulation is shown by the arrow G in fig. 1 and 2). The vacuum pump 2 is particularly referred to as "dry" because, in operation, the rotor 8 rotates inside the stator 5 without any mechanical contact between one another or with the stator 5, making it possible to use no oil in the pumping stages T1-T5.

In this exemplary embodiment, the vacuum pump 2 of the dry vacuum pump type is a multi-stage rough vacuum pump. A rough vacuum pump is a positive displacement vacuum pump that uses two rotors to suck, transfer and then deliver the gas to be pumped at atmospheric pressure. According to another example, the vacuum pump 2 is of the roots blower type and comprises one or two pumping stages. The Roots blower type vacuum pump is installed in series and is located upstream of the roughing vacuum pump.

According to an exemplary embodiment, the

cooling elements

11a, 11b comprise a hydraulic circuit 16 in order to allow water to circulate, for example at ambient temperature (fig. 2).

The hydraulic circuit 16 is integrated, for example, in the stator 5. It surrounds the bearings of the shafts 6, 7, for example in a "U" shape, in order to cool them.

The

cooling elements

11a, 11b also comprise, for example, a valve 17 which can be operated to allow or cut off the circulation of water ("all or nothing" control).

The vacuum pump 2 comprises, for example, two

cooling elements

11a, 11b coupled to the stator 5, one

cooling element

11a, 11b being arranged at each axial end of the vacuum pump 2 (fig. 2). The cooling element 11a is associated with a pumping stage T1, known as the low-pressure pumping stage, the inlet of which communicates with the suction inlet 9 of the pump 2. The cooling element 11b is coupled to a pumping stage T5, called high-pressure pumping stage, the outlet of which communicates with the output 10 of the pump 2.

The vacuum pump 2 comprises, for example, two

temperature sensors

12a, 12b, which are arranged on the stator 5 and spaced apart from one another. One temperature sensor 12a is associated with, for example, the cooling element 11a on the side of the suction port 9. The temperature sensor 12a is mounted on the stator 5, for example in the region of the low-pressure pumping stage T1 (on the side of the suction opening 9). The temperature sensor 12b is associated with, for example, the cooling element 11b on the side of the output port 10. The temperature sensor 12b is mounted on the stator 5, for example in the region of the high-pressure pumping stage T5 (on the side of the outlet 10).

For example, the

temperature sensors

12a, 12b are located on the stator 5 at the midpoint between the two shafts 6, 7 and are aligned on a line parallel to the axes of the shafts 6, 7 (fig. 1).

The control unit 13 comprises one or more controllers or microcontrollers or processors and a memory for executing a series of program instructions implementing a method 100 for controlling the temperature of the vacuum pump 2, in which method the temperature of the vacuum pump 2 subjected to a variable pumping load is controlled by means of said at least one

cooling element

11a, 11b coupled to the stator 5, based on a temperature set point and a temperature measurement of the stator 5.

To this end, the control unit 13 is connected to at least one

temperature sensor

12a, 12b to receive temperature measurements of the stator 5 and to at least one

cooling element

11a, 11b, for example for operating the opening/closing of an associated valve 17 of the hydraulic circuit 16. The temperature control can be carried out independently on each cooling element, according to its own temperature set point and the associated respective temperature measurement of each

cooling element

11a, 11 b.

In operation, the vacuum pump 2 is subjected to variable pumping loads, which may vary between high or low gas flows.

The control unit 13 monitors whether the value of the parameter indicative of the pumping load is lower than a load threshold S (diagnostic step 101, fig. 3).

The parameter indicative of the pumping load is, for example, the current consumed by the vacuum pump 2 or the power consumed by the vacuum pump 2. The control unit 13 calculates, for example, an average value of the current or power flowing through or consumed during a period of time equal to or greater than the duration of the cycle of the processing steps P1, P2. For this purpose, the control unit 13 is connected, for example, to the output of a transmission that varies the speed of the motor of the vacuum pump 2.

If-and as long as-the value of the parameter indicative of the pumping load is higher than the load threshold S, it is considered that process steps P1, P2 are occurring in chamber 3.

In this case, the control unit 13 controls the temperature of the vacuum pump 2 using the

cooling elements

11a, 11b to reach a temperature set point, for example by closing the valve 17 to cut off the circulation of water when the temperature measurement is below the temperature set point and by opening the valve 17 to allow the circulation of water when the temperature measurement is equal to or above the temperature set point (process phase adjustment step 102).

The temperature set point is for example above 70 ℃.

If-and as long as-the value of the parameter indicative of the pumping load is below the load threshold S, it is considered that idling step I is occurring in chamber 3. In this case, the control unit 13 raises the temperature setpoint by means of the at least one cooling element 11a to control the temperature of the vacuum pump 2 (idle phase adjustment step 103).

The temperature set point can be raised to control the temperature by both cooling

elements

11a, 11b or only one of them, but preferably at least by the cooling element 11a coupled to the low pressure pumping stage T1, which is more difficult to regulate in terms of temperature because the heat exchange capacity between the rotor 8 and the stator 5 is not good enough at low pressures.

The increase in the temperature set point corresponds to, for example, at least 3% of the temperature set point, for example, more than 3 ℃. The increase in the temperature set point corresponds to, for example, at most 20%, for example, below 20 ℃, of the temperature set point. The increase in the temperature set point is, for example, about 6%, e.g., 5 ℃ of the temperature set point.

The control unit 13 controls the temperature of the vacuum pump 2 via the

cooling elements

11a, 11b, for example by actuating the water circulation valve 17, to reach the raised temperature set point reached during the process steps P1, P2.

When the parameter indicative of the pumping load has increased to exceed the load threshold S, it is considered that further process steps P1, P2 are ongoing in chamber 3.

The increased temperature set point may then be maintained for a predetermined additional length of time before switching the increased temperature set point back to the initial temperature set point (repair step 104).

The additional time period is predetermined such that it is possible to dispense with a sensor. It is for example longer than 10 minutes, for example 15 minutes. This reconditioning step 104 allows time for the stator 5 to warm up due to the higher pumping load of the process steps P1, P2. This avoids any further difference between the temperatures of the rotor 8 and stator 5 when returning to the initial temperature set point.

This can be better understood by looking at the graph in fig. 4, which shows the power curve consumed by the vacuum pump 2 at the pumping load (curve a), the temperature curve of the stator 5 measured by the temperature sensor 12a in the vicinity of the low-pressure pumping stage T1 (curve B), and one example of two temperature curves of the stator 5 measured by indicative means at the centre of the cooling element 11a associated with the stator 5 of the low-pressure pumping stage T1 (curves C and D), to provide an understanding of the invention.

In the first two hours, 80slm (135.12 Pa.m)³Gas flow/s) is periodically introduced into the chamber 3. Thus, the gas flow alternated between 80slm for 5 minutes and 0slm for 3 minutes. The power consumed, indicating the pumping load, therefore varies in a square wave mode (curve a) between 500 and 2000W, above a load threshold of for example 600W for more than 3 minutes (duration equal to the no-flow phase of the process step).

The control unit 13 controls the temperature of the vacuum pump 2 by means of the

cooling elements

11a, 11b to reach a temperature set point of 83 ℃ (process stage adjustment step 102). It can be seen that the temperature of the stator 5 measured by the temperature sensor 12a therefore fluctuates around the set-point temperature between 81 ℃ and 86 ℃ due to the all-or-nothing regulation mode (curve B). It can also be seen that the temperature measured (by way of indication) in the center of the cooling element 11a fluctuates between 84 ℃ and 87 ℃ (curves C and D).

The consumed power then drops below the load threshold S. Thereby, the control unit 13 concludes that an idling step I is occurring in the chamber 3. Thus, the control unit 13 raises the temperature setpoint by 5 ℃ (idle stage adjustment step 103) and controls the temperature of the vacuum pump 2 to 88 ℃ by means of the cooling element 11a of the low-pressure pumping stage T1 and the temperature of the vacuum pump 2 to 83 ℃ or 88 ℃ by means of the cooling element 11b of the high-pressure pumping stage T5.

It can be noted that the temperature of the stator 5 measured by the temperature sensor 12a associated with the cooling element 11a has jumped by about 5 deg.c, fluctuating between 86 deg.c and 90 deg.c (curve B).

It can also be seen that the temperature measured at the center of the cooling element 11a increases rapidly due to the increase in the temperature set point and then decreases due to the decrease in the pumping load until it tends to stabilize at a temperature close to process step P1 (curves C and D).

Thus, the change in the temperature set point allows the cooling element 11a to more quickly shut off cooling of the stator 5, causing the stator 5 to preheat in the vicinity of the cooling element 11 a. Despite the temperature drop, there are few, if any, cases where the temperature of the stator 5 measured at the cooling element 11a has dropped below the temperature of process step P1. Thus, the temperature difference between the stator 5 and the rotor 8 during process step P1 is substantially the same as the temperature difference during idle step I, taking into account that the rotor 8 remains hot.

The power consumed then increases to exceed the load threshold S (curve a), which indicates that a further process step P2 is being performed in chamber 3. The temperature setpoint remains raised to 88 ℃ for 15 minutes (repair step 104): it can be seen that the temperature of the stator 5 starts to rise again in the region of the cooling element 11a as the vacuum pump 2 heats up (curves C and D).

After a predetermined additional length of time has elapsed, the control unit 13 lowers the temperature set point, which is returned to 83 ℃ (process stage adjustment step 102), since the temperature in the center of the cooling element 11a has returned approximately to the previous value of process step P1. The temperature at the center of the cooling element 11a decreases by the difference from the temperature set point and then slowly increases again to 83 ℃ with the value of the set point. During the idling step I and the following process step P2, the temperature of the region of the stator 5 close to the cooling element 11a is kept above 83 ℃.

Raising the temperature setpoint during idle step I at low pumping loads may allow the stator 5 to maintain the same high temperature in the centre of the cooling element 11a as during process steps P1, P2, which makes it possible to limit the risks of jamming or of the rotors 8 coming into contact with each other during idle step I, which are related to the difference in thermal expansion between the rotors 8 and the stator 5.

Maintaining a high temperature during idle step I may also make it possible to avoid the formation of cold zones where contaminating condensable substances may solidify or condense.

The variation of the temperature set point triggered by monitoring the pumping load also allows the method to be highly responsive.

Furthermore, by incorporating the thermal behavior of the vacuum pump 2 into the determination of the temperature control, the monitoring can be further performed based on the information already provided by the sensors of the vacuum pump 2, without adding additional temperature sensors, without providing information about the process being performed in the chamber 3, and without changing the position of the at least one

temperature sensor

12a, 12b or the structure of the

cooling element

11a, 11 b.

Claims

1. A method (100) for controlling the temperature of a vacuum pump (2) of the dry vacuum pump type subjected to a variable pumping load, the vacuum pump (2) comprising:

o a stator (5),

o at least one pumping stage (T1-T5),

o two shafts (6, 7) extending into the at least one pumping stage (T1-T5) and carrying respectively at least one rotor (8), these rotors (8) being configured to rotate synchronously in opposite directions in the stator (5) to drive a gas (G) to be pumped from a suction inlet (9) to an output (10) of the vacuum pump (2),

o at least one cooling element (11a, 11b) coupled to the stator (5),

o at least one temperature sensor (12a, 12b) configured to make a measurement of the temperature of the stator (5), an

A control unit (13) configured to control the temperature of the stator (5) by means of the at least one cooling element (11a, 11b) and the at least one temperature sensor (12a, 12b),

wherein the temperature of the vacuum pump (2) is controlled by means of said at least one cooling element (11a, 11b) coupled to the stator (5) as a function of a temperature setpoint and a temperature measurement of the stator (5), characterized in that it is monitored whether a value of a parameter indicative of the pumping load, selected from the power consumed or current drawn by the vacuum pump (2), is lower than a load threshold (101), and in that the temperature setpoint (103) is increased if the value of the parameter indicative of the pumping load is lower than the load threshold (S).

2. The temperature control method (100) according to the preceding claim, wherein the temperature setpoint is raised at least for temperature control by means of a cooling element (11a) coupled with a pumping stage (T1), referred to as low-pressure pumping stage, of the vacuum pump (2).

3. The temperature control method (100) according to one of the preceding claims, wherein after the temperature setpoint has been raised, it is monitored whether the value of the parameter indicative of the pumping load is above a load threshold (S), and, if the value of the parameter indicative of the pumping load is above the load threshold (S), the raised temperature setpoint is maintained (104) for a predetermined additional length of time.

4. The temperature control method (100) according to the preceding claim, wherein the predetermined additional length of time is greater than ten minutes.

5. The temperature control method (100) according to one of the preceding claims, wherein the rise value of the temperature set point is greater than 3 ℃.

6. The temperature control method (100) according to one of the preceding claims, wherein the temperature set point is raised by a value of less than 20 ℃.

7. Vacuum pump (2) of the dry vacuum pump type, comprising:

-a stator (5),

-at least one pumping stage (T1-T5),

-two shafts (6, 7) extending into the at least one pumping stage (T1-T5) and carrying respectively at least one rotor (8), these rotors (8) being configured to rotate synchronously in opposite directions in the stator (5) to drive a gas (G) to be pumped from a suction inlet (9) to an output outlet (10) of the vacuum pump (2),

-at least one cooling element (11a, 11b) coupled with the stator (5),

-at least one temperature sensor (12a, 12b) configured to make a measurement of the temperature of the stator (5), an

-a control unit (13) configured to control the temperature of the stator (5) by means of the at least one cooling element (11a, 11b) and the at least one temperature sensor (12a, 12b),

characterized in that said control unit (13) is configured to perform a temperature control method (100) according to one of the preceding claims.

8. Vacuum pump (2) of the dry vacuum pump type according to the preceding claim, characterized in that it is a rough vacuum pump.

9. Vacuum pump (2) of the dry vacuum pump type, according to claim 7 or 8, characterized in that it comprises two cooling elements (11a, 11b) coupled with the stator (5), one cooling element (11a, 11b) being arranged at each axial end of the vacuum pump (2).

10. Apparatus (1) comprising a chamber (3), characterized in that it comprises a vacuum pump (2) of the dry vacuum pump type according to one of claims 7 to 9, connected to the chamber (3) for pumping in said chamber (3).