Dry vacuum pump

Abstract

The present invention relates to a dry vacuum pump comprising a drive device 1 including a drive shaft 3 and at least two parallel rotors 7, 8, each having a rotor shaft 9, 10 provided with a rotor section 11, 12, at one end of which at least one drive wheel 4 is fixed, which is arranged to operate at least one belt 5, the rotor shafts 9, 10 being rotatably driven by the belt 5 and provided with toothed wheels 13, 14 at one of their axial ends. The pump is characterized in that the drive wheels 4 and the belt 5 are smooth, the shafts 9, 10 of the rotors 7, 8 each have at least one smooth section 16, 17 arranged to cooperate with the belt 5, and the toothed wheels 13, 14 of the shafts 9, 10 of the rotors 7, 8 are dimensioned and arranged to mesh with each other.

Description

Technical Field

[0001] The present invention relates to a dry vacuum pump, for example, a dry compression vacuum pump used in a so-called white room or clean room. More specifically, the present invention relates to a dry vacuum pump provided with a driving part by a belt. Still more specifically, the present invention relates to a dry vacuum pump of, for example, a positive displacement type, and particularly to a Roots pump type dry vacuum pump provided with a driving device that ensures optimal synchronization of the rotation of the rotor without the need to use a lubricating liquid.

Background Art

[0002] Dry vacuum pumps such as Roots pumps are well known in the current state of the art. Such pumps generally include two rotor parts arranged in a pump chamber, and these rotor parts are designed as rotor parts in the form of lobes in a Roots pump. Each rotor part is supported by a rotor shaft that is rotationally driven by a driving device.

[0003] In many conventionally known pumps, the driving device is constituted by two toothed wheels respectively attached to one of the rotor shafts and meshing with each other. One of the two shafts is rotationally driven by a motor, for example, an electric motor, and drives the second rotor shaft by the toothed wheel.

[0004] A driving device provided with a toothed wheel for transmitting the driving torque of one of the rotor shafts to the other rotor shaft has the advantage of being able to automatically synchronize the rotations of the two rotor shafts by the use of such a wheel. In order to obtain an efficient compression process and good output, it is necessary to reduce the gap between the rotor parts, and for that purpose, very accurate synchronization is required. Furthermore, whether intentionally or due to a failure, when the pump stops, the toothed wheel functions as a "landing gear", so it is possible to prevent damage to the rotor parts.

[0005] The drawback of this type of device lies in the constant contact required for the transmission of drive torque, which exists between the toothed wheels and requires lubrication. In fact, without lubrication, the toothed wheels would wear out immediately, thereby causing the rotor shaft to lose synchronization, reducing the efficiency of the pump, and ultimately damaging the rotor part. Unfortunately, in many applications, the use of lubricating fluids is not desirable because it leads to the contamination of the evacuated vacuum chamber. This is, for example, a recurring problem in the semiconductor field, where such contamination is highly incompatible with the manufacturing processes employed.

[0006] Another method for enabling the synchronization of the rotor shafts of vacuum pumps is disclosed in Patent Document 1. Patent Document 1 describes a dry screw pump in which the rotor shafts are each driven by a dedicated electric motor and the angular position of the shafts is determined by a resolver. The motors of the rotor shafts are electronically synchronized based on the signals of the resolver. This method enables efficient synchronization of the rotor shafts but requires the use of two separate motors and an electronic system, the use of which is not desirable in many applications.

[0007] In Patent Document 2, it has been proposed to use a toothed belt actuated by the toothed wheels of a drive device to drive the rotor shafts of a dry screw pump. This has the advantage of making it possible to separate the toothed wheels attached to the rotor shafts. Since there is no contact between the toothed wheels, lubrication is no longer necessary.

[0008] However, this type of drive using a toothed belt has a major drawback in that it cannot sufficiently synchronize the rotor shafts. In order to prevent damage to the rotor part due to the desynchronization of the rotor shafts, Patent Document 2 proposes using a rotor part with a larger play. Unfortunately, this means that pumps using this type of drive unit have to be provided with a much longer rotor part and have a larger number of compression pockets in order to achieve the same compression ratio as a normal pump.

[0009] Accordingly, an object of the present invention is to propose a dry vacuum pump provided with a drive device that guarantees sufficient synchronization of the rotor shafts so that it can be used in a conventional dry vacuum pump such as a roots pump without requiring lubrication.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Summary of the Invention

[0011] The main object of the present invention is to propose a dry vacuum pump provided with a rotor drive mechanism that is more efficient than conventional pumps.

[0012] According to the present invention, these objects are achieved through the subject matter of the independent claims. More specific aspects of the present invention are described in the dependent claims and in this specification.

[0013] More specifically, the object of the present invention is achieved through a dry vacuum pump, comprising a drive device including a drive shaft, and at least two parallel rotors each having a rotor shaft provided with a rotor part. At one end of the drive shaft, at least one drive wheel provided to operate at least one belt is fixed. The rotor shaft can be rotationally driven by the belt, and a toothed wheel is provided at one of its axial end portions. The drive wheel and the belt are smooth, and each shaft of the rotor has at least one smooth section arranged to cooperate with the belt. The toothed wheels of the shafts of the rotors are dimensioned and arranged to mesh with each other.

[0014] By driving with the belt and automatically synchronizing the rotors with the toothed wheels, it becomes possible to minimize the play between the rotor parts, thereby ensuring the maximum efficiency of the pump, particularly its compression ratio, without the need to change the pump's rotor, rotor part, and / or stator. In other words, the drive device of the present invention can be adapted to existing pumps without changing the rotor part and stator and without sacrificing efficiency.

[0015] In fact, the toothed wheels of the rotor shafts enable automatic synchronization of the rotation of the rotor shafts. For example, if desynchronization of the rotor shafts occurs due to belt slippage, the toothed wheels can automatically resynchronize the rotor shafts. Since the toothed wheels are only loaded when resynchronization is required, these wheels do not require lubrication. When the two shafts are synchronized, the toothed wheels mesh with each other but are not loaded, thereby avoiding wear of the toothed wheels. In fact, unlike known prior art pumps, the rotational torque is transmitted by the belt rather than the toothed wheels.

[0016] Furthermore, for example, when the belt is damaged, the gear composed of the toothed wheels of the rotor shaft enables the integral rotation of these two rotor shafts to be maintained. Therefore, the toothed wheel functions as a "landing gear", that is, a safety gear. In the event of a belt failure, the toothed wheel enables the pump to decelerate until it stops without the rotors coming into contact and causing damage.

[0017] Therefore, in the pump according to the present invention, it is possible to eliminate the need for lubrication while ensuring optimal synchronization of the rotor shafts. Finally, the pump according to the present invention can avoid damage to the rotor part even when the drive of the pump suddenly stops, for example, in the event of a belt break or a power outage. It is important to note that the pump according to the present invention can be provided with any type of motor that drives the drive wheel. This motor may be, for example, an electric motor or a thermal motor.

[0018] In a preferred embodiment of the present invention, the toothed wheels are arranged such that a load is applied to the teeth of each toothed wheel only when the rotor shafts are rotationally driven asynchronously. This minimizes wear damage to the toothed wheels and enables the service life of the drive device to be longer.

[0019] In another preferred embodiment of the present invention, the angular play of the toothed wheel is less than the angular play of the rotor part. This causes a load to be applied to the toothed wheel before the rotor parts come into contact with each other, thereby enabling the rotor parts not to be damaged even when the pump suddenly stops.

[0020] In a preferred embodiment according to the present invention, the smooth section of each rotor shaft is located at one end of the shaft. Thereby, a compression zone for effectively transferring and compressing the discharged fluid by the rotor part supported by the rotor shaft, and a drive device of the rotor shaft, in particular, a drive zone including the smooth section and the belt of each rotor shaft can be easily separated. As a result, it is possible to prevent the compression zone from being contaminated by the drive zone.

[0021] In another preferred embodiment of the present invention, the smooth section has a diameter smaller than the diameter of the toothed wheel on each rotor shaft.

[0022] In a preferred embodiment according to the present invention, the two toothed wheels have the same diameter, and the two smooth sections have the same diameter. Thereby, it becomes possible to facilitate the synchronization of the rotation of the rotor shaft. In fact, by making the same diameter, the rotor shaft can be easily rotated at the same speed.

[0023] In still another preferred embodiment of the present invention, the belt partially surrounds one of the smooth sections and is pushed downward by the other smooth section. Thereby, it is possible to easily drive the two rotor shafts to rotate in opposite directions. In a conventionally known dry vacuum pump, for example, a screw pump, a Roots pump, or a claw pump, etc., a rotor shaft that is usually scheduled to be rotationally driven in opposite directions to each other is employed, and the drive device of the pump according to the present invention can be applied to drive such a conventionally known pump.

[0024] In another preferred embodiment of the present invention, the toothed wheel and the smooth section of the rotor shaft are located at the same axial end of the shaft. Thereby, it becomes possible to provide a simple geometry of the belt that prevents the risk of energy loss and belt breakage.

[0025] In another preferred embodiment of the present invention, each smooth section is located on the circumferential surface of the disc-shaped portion. Thereby, in particular, the contact surface between the belt and the rotor shaft can be increased, and it becomes possible to optimize the driving of the rotor shaft by the belt. In addition, the risk of slippage of the belt with respect to the smooth section is reduced, and the risk of desynchronization of the rotor shaft can be reduced.

[0026] In a preferred embodiment according to the present invention, the disc-shaped portion and the drive wheel are in substantially the same plane. Thereby, it becomes possible to position the belt in the same plane and reduce the risk of breakage of the belt.

[0027] In another preferred embodiment of the present invention, the points resulting from the projections of the rotation axes of the rotor shaft and the drive shaft are aligned on a plane perpendicular to those rotation axes. For this reason, the pressure of the belt in the smooth section of the rotor shaft becomes equal, and thereby, optimal drive synchronization can be realized.

[0028] In yet another preferred embodiment of the present invention, the distance between the drive shaft and the rotor shaft closest to the drive shaft is adjustable. Thereby, it becomes possible to adjust the tension of the drive belt and optimize the driving of the rotor shaft. By adjusting the tension of the belt, the risk of desynchronization of the rotor shaft can be minimized, and thus, it is possible to prevent the toothed wheel from contacting to re-establish synchronization.

[0029] In yet another preferred embodiment of the present invention, the dry vacuum pump is a dry vacuum pump in which the rotor portions have a lobe shape and fit together.

[0030] In a preferred embodiment according to the present invention, the vacuum pump is a Roots pump, a screw pump, or a claw pump.

[0031] In another preferred embodiment of the present invention, the vacuum pump is single-stage or multi-stage.

[0032] Also, in another preferred embodiment of the present invention, the drive device includes a drive shaft, and at least one drive wheel for operating two belts is fixed to one end of the drive shaft.

[0033] Other advantages and features of the present invention will be described in detail below with reference to the accompanying drawings schematically shown below.

Brief Description of the Drawings

[0034]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0035] The dry vacuum pump according to the present invention is an assembly including a drive device 1 that rotationally drives a drive shaft 3, usually an electric motor, and at least one drive wheel 4 provided to operate at least one belt 5 is fixed to the front end of the drive shaft 3.

[0036] Figure 1 shows a dry vacuum pump according to a first preferred embodiment of the present invention, which is a dry Roots pump type dry vacuum pump. Such a dry vacuum pump is an assembly including a driving device 1 that rotationally drives a driving shaft 3, usually an electric motor 2. At the front end of the driving shaft 3, a driving wheel 4 provided to operate a belt 5 is fixed.

[0037] A housing is fixed adjacent to the driving device 1. The housing has a lower part 6 and an upper part (not shown), and at least two rotors 7, 8 are mounted inside so as to rotate freely. Each of the rotors 7, 8 is provided with a rotor part formed as lobes 11, 12 in the illustrated example, and includes rotor shafts 9, 10 that are rotationally driven by a belt 5. Each of the rotor shafts 9, 10 is provided with toothed wheels 13, 14 at one of the axial ends, preferably at the front end.

[0038] As shown in Figure 2, the rotational axes of the rotor shafts 9, 10 of the two rotors 7, 8 are parallel to each other, and usually, similarly, parallel to the rotational axis of the driving shaft 3.

[0039] The lobes 11, 12 are generally the same, and the distance between the rotational axes of the rotor shafts 9, 10 of the rotors 7, 8 is selected so that these lobes 11, 12 can interact with each other so as to achieve volumetric transfer and compression of the fluid to be discharged, as is well known to those skilled in the art. Since the rotors 7, 8 are provided to rotate in opposite directions to each other, their lobes 11, 12 rotate at an angle of 90° to each other (see Figure 3).

[0040] An inlet orifice (not shown) for a fluid such as air is provided at the rear of the housing, and an outlet orifice (not shown) for this fluid is provided at the front. Therefore, the rotation of the lobes 11, 12 brings about the circulation and compression of the fluid.

[0041] According to the present invention, the belt 5 is as smooth as the drive wheel 4, that is, this drive wheel 4 has a smooth axial peripheral surface 15.

[0042] The smooth drive wheel 4 is in close contact with the drive wheel 4 and is configured to cooperate with a belt 5 that can be actuated by the rotation of the shaft 3 of the motor 2.

[0043] The belt 5 is similarly provided to rotate the rotor shafts 9, 10 of the rotors 7, 8 and act on the rotor shafts 9, 10. These rotor shafts 9, 10 have sections with smooth axial peripheral surfaces that receive the belt 5 and are in close contact with the belt 5. Therefore, these smooth sections 16, 17 are located at the front ends of the shafts 9, 10 of the rotors 7, 8.

[0044] As particularly shown in FIG. 4, the belt 5 forms a loop from the drive wheel 4 to the first rotor shaft, that is, the rotor shaft 9 farthest from the drive wheel 4. Therefore, the belt 5 is looped around the smooth axial peripheral surface 15 of the drive wheel 4 and the smooth section 16 of the rotor shaft 9 and extends between this rotor shaft 9 and this drive wheel 4.

[0045] However, so that the second rotor shaft 10 disposed between the first rotor shaft 9 and the drive wheel 4 can also be driven, the belt 5 needs to contact and adhere closely to the smooth section 17 of this second rotor shaft 10. This is achieved by deforming the path of the belt 5, which becomes trapezoidal when there is one shaft. Therefore, the path of the belt 5 is bent so that the belt 5 passes under the smooth section 17 of the second rotor shaft 10.

[0046] Therefore, the belt 5 partially surrounds the wheel 4 of the drive device 1 and the smooth section 16 of the first rotor shaft 9 and is pushed downward by the smooth section 17 of the second rotor shaft 10.

[0047] As shown by the line L depicted in FIG. 4, the points resulting from the projections of the axes of rotation of the rotor shafts 9, 10 of the rotors 7, 8 and the axis of rotation of the drive shaft 3 are preferably aligned on a plane perpendicular to those axes of rotation.

[0048] The length of the belt 5 and / or the distance between the drive device 1 and the housing are selected such that the belt 5 is maintained in a sufficiently extended state so as to be able to play a role in rotationally driving the first rotor shaft 9 and the second rotor shaft 10 of the rotors 7, 8.

[0049] Also, the distance between the drive device 1 (or the drive shaft 3) and the housing (or the second rotor shaft 10 of the rotor 8) may be made adjustable, thereby enabling the use of a variable-length belt and enabling the tension of the belt 5 to be optimally adjusted.

[0050] The rotor shafts 9, 10 of the rotors 7, 8 preferably each have disc-shaped portions 19, 20 for increasing the diameters of the rotor shafts 9, 10 in order to facilitate rotational driving. The axial peripheral surfaces of the disc-shaped portions 19, 20 are smooth and constitute the smooth sections 16, 17 of the rotor shafts 9, 10. The disc-shaped portions are preferably pulleys. The disc-shaped portions 19, 20 and the drive wheel 4 are substantially in the same plane so as to be able to effectively cooperate with the belt 5. The axial thicknesses of the disc-shaped portions 19, 20 and the drive wheel 4 are generally at least equal to the axial thickness of the belt 5.

[0051] According to the present invention, preferably at the front end portions of the rotor shafts 9, 10, the toothed wheels 13, 14 supported by the rotor shafts 9, 10 are dimensioned to mesh with each other and are located on the same plane. Therefore, the sum of the radii of these toothed wheels 13, 14 is substantially equal to the distance between the two axes of rotation of the rotor shafts 9, 10 of the rotors 7, 8, taking into account the dimensions of the teeth.

[0052] According to the present invention, it is important to note that the toothed wheels 13, 14 are dimensioned such that a load is applied to the teeth of these wheels only when the rotations of the rotor shafts 9, 10 are asynchronous. Otherwise, the toothed wheels 13, 14 mesh well with each other and their teeth do not receive a load. In fact, the gear formed by the toothed wheels 13, 14, unlike the pumps of the known prior art, does not have the function of transmitting torque from one rotor shaft to the other rotor shaft. The toothed wheels 13, 14 have solely the function of automatically synchronizing the rotations of the rotor shafts 9, 10. Therefore, the toothed wheels 13, 14 do not need to be lubricated and it is possible not to use a lubricating fluid for the entire drive device of the pump.

[0053] By ensuring the optimal synchronization of the rotor shafts 9, 10, and thus the optimal synchronization of the rotors 7, 8, it is possible to expect that the play between the rotor parts 11, 12, and the play between the pump housing, more specifically between the stator part of the pump, is smaller compared to the play present in the prior art pumps provided with a toothed belt. By reducing the play between the rotor parts 11, 12, the compression chambers formed by the rotations of the rotor parts 11, 12 can have less leakage, and thus, for the same pump size, a higher compression ratio can be achieved.

[0054] In addition, even when the belt 5 is damaged or the pump stops, the gear formed by the toothed wheels 13, 14 functions as a "landing gear", thereby preventing the lobes 11, 12 from rubbing against each other and avoiding damage to the lobes 11, 12. In fact, the toothed wheels 13, 14 can stop the synchronized rotors 7, 8 without damaging them.

[0055] The smooth sections 16, 17 of the rotor shafts 9, 10 of the rotors 7, 8 preferably have a diameter smaller than the diameter of the toothed wheels 13, 14 supported by these shafts 9, 10.

[0056] The toothed wheels 13, 14 are generally of the same diameter, and the two smooth sections 16, 17 are also generally of the same diameter, regardless of whether they are located on the disc-shaped portions 19, 20.

[0057] Fig. 5 shows a dry vacuum pump according to a second preferred embodiment of the present invention, which is a dry Roots pump type dry vacuum pump. Such a dry vacuum pump is an assembly including a driving device 1 having a motor 2, which is usually an electric motor, for rotationally driving a driving shaft 3. At the front end of the driving shaft 3, at least one driving wheel 4 is fixed, which is provided to operate two belts 5a, 5b.

[0058] According to this embodiment, the two belts 5a, 5b are as smooth as the driving wheel 4, that is, the driving wheel 4 has a smooth axial peripheral surface 15.

[0059] The smooth driving wheel 4 is in close contact parallel to the driving wheel 4 and is adapted to cooperate with two belts 5a, 5b that can be operated by the rotation of the shaft 3 of the motor 2. In this embodiment, the smooth driving wheel 4 has a separation groove defining the boundary of two smooth regions, which is intended to axially receive and hold each of the two belts 5a, 5b.

[0060] According to a variant, the driving device 1 includes a driving shaft 3, and at the front end of the driving shaft 3, two driving wheels 4 are fixed, which are provided to operate two belts 5a, 5b.

[0061] The two belts 5a, 5b are also provided to rotate the rotor shafts 9, 10 of the rotors 7, 8 and act on the rotor shafts 9, 10. These rotor shafts 9, 10 have sections with smooth axial circumferential surfaces that receive the two belts 5a, 5b in parallel and are brought into close contact with the two belts 5a, 5b. Therefore, these smooth sections 16, 17 are located at the front ends of the shafts 9, 10 of the rotors 7, 8 and have separation grooves that define the boundaries of the two smooth portions of each rotor shaft 9, 10, being configured to axially receive and hold each of the two belts 5a, 5b.

[0062] As can be seen particularly in FIG. 5, the two belts 5a, 5b each form a loop in parallel from the drive wheel 4 to the first rotor shaft, i.e., the rotor shaft 9 farthest from the drive wheel 4. Therefore, the two belts 5a, 5b are each hung in parallel on the smooth axial circumferential surface 15 of the drive wheel 4 and the smooth section 16 of the rotor shaft 9 and extend between the rotor shaft 9 and the drive wheel 4.

[0063] However, in order for the second rotor shaft 10 disposed between the first rotor shaft 9 and the drive wheel 4 to also be driven, the two belts 5a, 5b need to be in contact with and closely adhere to the smooth section 17 of the second rotor shaft 10 in parallel. This is achieved by deforming the paths of the two belts 5a, 5b, which would be trapezoidal if there were only one shaft. Therefore, the paths of the two belts 5a, 5b are bent so as to pass under the smooth section 17 of the second rotor shaft 10 (see FIGS. 5 and 6).

[0064] Therefore, the belts 5a, 5b partially surround the wheel 4 of the drive device 1 and the smooth section 16 of the first rotor shaft 9 and are pushed downward by the smooth section 17 of the second rotor shaft 10 (see FIG. 6).

[0065] The rotor shafts 9, 10 of the rotors 7, 8 preferably each have disc-shaped portions 19, 20 that increase the diameter of the rotor shafts 9, 10 to facilitate rotational drive. The axial circumferential surfaces of the disc-shaped portions 19, 20 are smooth and have separation grooves that define the boundaries of two smooth zones intended to axially receive and hold each of the two belts 5a, 5b. Further, the disc-shaped portions 19, 20 constitute smooth sections 16, 17 of the rotor shafts 9, 10 (see FIG. 7).

[0066] In one variant form, the rotor shafts 9, 10 of the rotors 7, 8 each have two disc-shaped portions 19, 20.

[0067] The disc-shaped portions 19, 20 and the drive wheel 4 are in substantially the same plane so as to be able to cooperate effectively with the two belts 5a, 5b. The axial thicknesses of the disc-shaped portions 19, 20 and the drive wheel 4 are generally at least equal to the axial thicknesses of the two belts 5a, 5b (see FIG. 7).

[0068] In the embodiments shown in FIGS. 6 and 8, the disc-shaped portions 19, 20 are provided with bearings 21a, 21b such as seal bearings, ball bearings, or deep groove ball bearings.

[0069] Generally, the risk of the belt slipping is related to the torque and grip angle of the belt in the disc-shaped portion. In an advantageous aspect, according to a second preferred embodiment of the present invention, the two belts 5a, 5b are each independently exposed to the risk of slipping, so that the work of resynchronizing the toothed wheels can be further reduced. Therefore, by ensuring the risk of slipping by using the two belts 5a, 5b, the risk of desynchronization and wear damage of the toothed wheels can be reduced and limited.

[0070] It is apparent that the present invention can be implemented with many variations. Although two non-limiting embodiments have been described by way of example, it is fully understood that it is not possible to comprehensively identify all possible variations. Of course, it is possible to replace the described means with equivalent means without departing from the scope of the present invention. All of these changes form part of the common knowledge of those skilled in the art in the field of vacuum pumps. In particular, those skilled in the art will readily understand that the belt drive device of the present invention can be used in any type of positive displacement pump, such as a screw pump or a claw pump, that employs two rotors that are rotationally driven, regardless of whether the belt drive device is lubricated or dry, or whether it is single-stage or multi-stage.

Claims

1. A drive device (1) including a drive shaft (3), and at least two parallel rotors (7, 8) each having a rotor shaft (9, 10) provided with rotor parts (11, 12), comprising: At one end of the drive shaft (3), at least one drive wheel (4) provided to operate at least one belt (5) is fixed, The rotor shafts (9, 10) can be rotationally driven by the belt (5), and a toothed wheel (13, 14) is provided at one of its axial end portions, The drive wheel (4) and the belt (5) are smooth, Each rotor shaft (9, 10) of the rotors (7, 8) has at least one smooth section (16, 17) arranged to cooperate with the belt (5), The toothed wheels (13, 14) of the rotor shafts (9, 10) of the rotors (7, 8) are dimensioned and arranged to mesh with each other, characterized by a dry vacuum pump.

2. The toothed wheels (13, 14) are arranged such that a load is applied to the teeth of each toothed wheel only when the rotor shafts (9, 10) are rotationally driven asynchronously. The dry vacuum pump according to claim 1.

3. The angular play of the toothed wheels (13, 14) is less than the angular play of the rotor parts (11, 12). The dry vacuum pump according to claim 1 or 2.

4. The smooth sections (16, 17) of each rotor shaft (9, 10) of the rotors (7, 8) are located at one end of the rotor shaft (9, 10). The dry vacuum pump according to any one of claims 1 to 3.

5. The smooth sections (16, 17) have a diameter smaller than the diameter of the toothed wheels (13, 14) on each rotor shaft (9, 10) of the rotors (7, 8). The dry vacuum pump according to any one of claims 1 to 4.

6. The two toothed wheels (13, 14) have the same diameter, The two smooth sections (16, 17) have the same diameter. The dry vacuum pump according to any one of claims 1 to 5.

7. The belt (5) partially surrounds one of the smooth sections (16, 17), namely the smooth section (16), and is pushed downward by the other smooth section (17). The dry vacuum pump according to any one of claims 1 to 6.

8. The toothed wheels (13, 14) and the smooth sections (16, 17) of the rotor shafts (9, 10) of the rotors (7, 8) are located at the same axial end of the rotor shafts (9, 10). The dry vacuum pump according to any one of claims 1 to 7.

9. Each smooth section (16, 17) is located on the circumferential surface of a disc-shaped portion (19, 20). The dry vacuum pump according to any one of claims 1 to 8.

10. The disc-shaped portions (19, 20) and the drive wheel (4) are substantially in the same plane. The dry vacuum pump according to claim 9.

11. The points resulting from the projections of the rotation axes of the rotor shafts (9, 10) of the rotors (7, 8) and the rotation axis of the drive shaft (3) are aligned on a plane perpendicular to those rotation axes. The dry vacuum pump according to any one of claims 1 to 10.

12. The distance between the drive shaft (3) and the rotor shaft (10) closest to the drive shaft (3) is adjustable. The dry vacuum pump according to any one of claims 1 to 11.

13. The dry vacuum pump is a dry vacuum pump in which the rotor parts (11, 12) have a lobe shape that fits together. The dry vacuum pump according to any one of claims 1 to 12.

14. The dry vacuum pump is a Roots pump, a screw pump, or a claw pump. The dry vacuum pump according to any one of claims 1 to 12.

15. The dry vacuum pump is single-stage or multi-stage. The dry vacuum pump according to any one of claims 1 to 14.

16. The drive device (1) includes a drive shaft (3). At one end of the drive shaft (3), at least one drive wheel (4) for operating two belts (5a, 5b) is fixed. The dry vacuum pump according to any one of claims 1 to 15.

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