DRY VACUUM PUMP

Abstract

The present invention concerns a dry vacuum pump comprising: a drive device (1) comprising a drive shaft (3) at one end of which is fixed at least one drive wheel (4) provided to set in motion at least one belt (5); at least two parallel rotors (7, 8) each having a shaft (9, 10) provided with a rotor element (11, 12), this shaft (9, 10) being able to be driven in rotation by the belt (5) and being equipped at one of its axial ends with a toothed wheel (13, 14), this pump having the special features that: the drive wheel (4) and the belt (5) are smooth; each shaft (9, 10) of the rotor (7, 8) comprises at least one smooth section (16, 17) arranged to co-operate with the belt (5), and the toothed wheels (13, 14) of the shafts (9, 10) of the rotor (7, 8) are dimensioned and arranged to mesh with one another.

Claims

1. Dry vacuum pump comprising: a drive device comprising a drive shaft at one end of which is fixed at least one drive wheel provided to set in motion at least one belt; at least two parallel rotors each having a rotor shaft provided with a rotor element, each said rotor shaft being drivable in rotation by the belt and being equipped at one of its axial ends with a toothed wheel, wherein the at least one drive wheel and the at least one belt are smooth; the rotor shaft of each rotor comprises at least one smooth section arranged to co-operate with the belt, and the toothed wheels of the rotor shafts of the respective rotors are dimensioned and arranged to mesh with one another.

2. Dry vacuum pump according to claim 1, wherein the toothed wheels are arranged so that teeth of the respective toothed wheels are subjected to a load only when the rotor shafts are driven in rotation asynchronously.

3. Dry vacuum pump according to claim 1, wherein an angular play of toothed wheels is less than that of the respective rotor elements.

4. Dry vacuum pump according to claim 1, wherein the smooth section of the rotor shaft of each rotor is situated at one end of the respective rotor shaft.

5. Dry vacuum pump according to claim 1, wherein, on the rotor shaft of each rotor, the smooth section has a diameter less than that of the respective toothed wheel.

6. Dry vacuum pump according to claim 1, wherein the toothed wheels are of the same diameter and the smooth sections are of the same diameter.

7. Dry vacuum pump according to claim 1, wherein the belt surrounds partially one of the smooth sections and is pushed downward by another of the smooth sections.

8. Dry vacuum pump according to claim 1, wherein the toothed wheel and the smooth section of a said rotor shaft of a said rotor are located at the same axial end of the respective rotor shaft.

9. Dry vacuum pump according to claim 1, wherein each smooth section is situated on a circumferential surface of a respective discoid part.

10. Dry vacuum pump according to claim 9, wherein the discoid parts and the drive wheel are substantially in the same plane.

11. Dry vacuum pump according to claim 1, wherein points coming from projections of axes of rotation of the rotor shafts, of the rotors, and of the drive shafts are aligned on a plane which is perpendicular to said axes of rotation.

12. Dry vacuum pump according to claim 1, wherein a distance between the drive shaft and the rotor shaft closest to it is adjustable.

13. Dry vacuum pump according to claim 1, wherein the pump is a dry vacuum pump where the rotor elements have the form of lobes fitted into one another.

14. Dry vacuum pump according to claim 1, wherein the vacuum pump is a Roots pump, a screw pump or a claw pump.

15. Dry vacuum pump according to claim 1, wherein the vacuum pump is single-staged or multi-staged.

16. Dry vacuum pump according to claim 1, wherein said at least one belt being two belts.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Other advantages and features of the invention will be described in detail in the following specification which is given with reference to the attached figures, which represent schematically:

[0039] FIG. 1: a dry vacuum pump, here a dry Roots pump, according to a first preferred embodiment of the present invention, in perspective top view;

[0040] FIG. 2: a part of the vacuum pump of FIG. 1;

[0041] FIG. 3: a part of the vacuum pump of FIG. 1 in which the pump housing is hidden;

[0042] FIG. 4: a front view of the vacuum pump of FIGS. 1 to 3;

[0043] FIG. 5: a dry vacuum pump, here a dry Roots pump, according to a second preferred embodiment of the present invention, in top view and in perspective;

[0044] FIG. 6: a front view of the vacuum pump of FIG. 5;

[0045] FIG. 7: a top view of the vacuum pump of FIG. 5; and

[0046] FIG. 8: a front view of the vacuum pump in cross section along the plane A-A of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

[0047] The dry vacuum pump according to the present invention is an assembly comprising a drive device 1 comprising a motor 2, generally electric, driving in rotation a drive shaft 3, at the front end of which is fixed at least one drive wheel 4 provided to set in motion at least one belt 5.

[0048] The dry vacuum pump, according to a first preferred embodiment of the present invention, here in the form of a dry Roots pump and represented in FIG. 1, is an assembly comprising a drive device 1 comprising a motor 2, generally electric, driving in rotation a drive shaft 3 at the front end of which is fixed a drive wheel 4 provided to set in motion a belt 5.

[0049] Fixed next to the drive device 1 is a housing comprising a lower part 6 and an upper part (not shown) and in which are mounted, in a way free to rotate, at least two rotors 7, 8. Each rotor 7, 8 includes a rotor shaft 9, 10 provided with a rotor element, here in the form of a lobe 11, 12, and intended to be driven in rotation by the belt 5. Each rotor shaft 9, 10 is equipped at one of its axial ends with a toothed wheel 13, 14, preferably on the front side.

[0050] As can be seen better in FIG. 2, the axes of rotation of the rotor shafts 9, 10 of the two rotors 7, 8 are parallel with respect to one another and generally likewise parallel to the axis of rotation of the drive shaft 3.

[0051] The lobes 11, 12 are generally identical and the distance between the axes of rotation of the rotor shafts 9, 10 of the rotors 7, 8 is selected in such a way that these lobes 11, 12 are able to interact in a way so as to be able to create a positive displacement and a compression of fluid to be evacuated as is well known to one skilled in the art. Because the rotors 7, 8 are provided to turn in opposite direction, their lobes 11, 12 are turned, one with respect to the other, at an angle of 90° (cf. FIG. 3).

[0052] 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 in the front. Thus, the rotation of the lobes 11, 12 brings about the circulation and the compression of the fluid.

[0053] According to the invention, the belt 5 is smooth, just like the drive wheel 4, which means that this drive wheel 4 has a smooth axial circumferential surface 15.

[0054] The smooth drive wheel 4 is intended to co-operate with the belt 5 which adheres to it and can, thanks to this, be set in motion by the rotation of the shaft 3 of the motor 2.

[0055] Since the belt 5 is likewise provided to act on the rotor shafts 9, 10 of the rotors 7, 8, by making them turn, these rotor shafts 9, 10 have sections whose axial circumferential surfaces are smooth to receive the belt 5 and make it adhere. These smooth sections 16, 17 are thus situated at the front end of the shafts 9, 10 of the rotors 7, 8.

[0056] As can be seen in particular in FIG. 4, the belt 5 forms a loop going from the drive wheel 4 to the first rotor shaft, that is to say the rotor shaft 9 farthest from the drive wheel 4. The belt 5 thus rests on the smooth axial circumferential surface 15 of the drive wheel 4 and the smooth section 16 of the rotor shaft 9, and it is stretched between this rotor shaft 9 and this drive wheel 4.

[0057] However, in order to be able to drive also the second rotor shaft 10 situated between the first rotor shaft 9 and the drive wheel 4, the belt 5 must come into contact with the smooth section 17 of this second rotor shaft 10 and adhere to it. This is achieved by deforming the path of the belt 5 which would be trapezoidal if there were only one shaft. Thus, the path of the belt 5 is bent by forcing it to pass under the smooth section 17 of the second rotor shaft 10.

[0058] Thus the belt 5 surrounds partially the wheel 4 of the drive device 1 and the smooth section 16 of the first rotor shaft 9, and it is pressed downward by the smooth section 17 of the second rotor shaft 10.

[0059] Preferably, the points coming from the projection of the axes of rotation of the rotor shafts 9, 10 of the rotors 7, 8 and of the drive shaft 3 are aligned on a plane which is perpendicular to them, as shown by the line L drawn in FIG. 4.

[0060] The length of the belt 5 and/or the distance between the drive device 1 and the housing are/is selected in such a way that the belt 5 remains sufficiently stretched to be able to fulfil its role of driving in rotation the first 9 and the second 10 rotor shafts of the rotors 7, 8.

[0061] Advantageously, it can be foreseen that 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) is adjustable, which makes it possible to use belts of variable length and to adjust the tension of the belt 5 in an optimal way.

[0062] In order to facilitate their driving in rotation, the rotor shafts 9, 10 of the rotors 7, 8 each preferably comprise a discoid part 19, 20 increasing their diameter and the axial circumferential surface of which is smooth and then constitutes the smooth section 16, 17 of the rotor shaft 9, 10 under consideration. Preferably, the discoid parts are pulleys. The discoid parts 19, 20 and the drive wheel 4 are substantially in the same plane, in such a way as to be able to co-operate effectively with the belt 5. Their axial thicknesses are generally at least equal to that of the belt 5.

[0063] According to the invention, the toothed wheels 13, 14 borne by the rotor shafts 9, 10, preferably at the front ends thereof, are dimensioned to mesh with one another and are situated in the same plane. The sum of the radii of these toothed wheels 13, 14 is thus 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.

[0064] It is important to note that, according to the invention, the toothed wheels 13, 14 are dimensioned in such a way that the teeth of these wheels are subjected to a load only when the rotation of the rotor shaft 9, 10 is asynchronous. The rest of the time the toothed wheels 13, 14 mesh well with each other, but their teeth do not undergo load. In fact, the gear formed by the toothed wheels 13, 14 does not have as a function to transmit torque from one rotor shaft to the other, contrary to known prior art pumps. The toothed wheels 13, 14 have solely a function of automatic synchronization of the rotation of the rotor shafts 9, 10. The toothed wheels 13, 14 thus do not need to be lubricated, and the entire drive device of the pump can do without lubricating liquid.

[0065] The guarantee of an optimal synchronization of the rotor shafts 9, 10 and thus of the rotors 7, 8, makes it possible to foresee rotor elements 11, 12 with reduced play between them and between the housing of the pump, more specifically the stator part of the pump, in comparison with play existing in prior art pumps equipped with toothed belts. A reduced play between the rotor elements 11, 12 makes it possible finally to achieve compression chambers created by the rotation of the rotor elements 11, 12 whose leaks are less great and thus a greater compression rate for the same pump size.

[0066] In addition, in the case of breakage of the belt 5 or in the case of stopping of the pump, the gear formed by the toothed wheels 13, 14 acts as “landing-gear” which makes it possible to avoid damage to the lobes 11, 12 by preventing them from rubbing against each other. In fact, the toothed wheels 13, 14 allow a stop of the synchronized rotors 7, 8 without them being damaged.

[0067] Preferably, the smooth sections 16, 17 of the rotor shafts 9, 10 of the rotors 7, 8 have diameters less than those of the toothed wheels 13, 14 borne by these shafts 9, 10.

[0068] The toothed wheels 13, 14 are generally of the same diameter, and the two smooth sections 16, 17, whether or not they are located on the discoid parts 19, 20, are also generally of the same diameter.

[0069] According to a second preferred embodiment of the present invention, the dry vacuum pump, represented in the form of a dry Roots pump in FIG. 5, is an assembly comprising a drive device 1 comprising a motor 2, generally electric, driving in rotation a drive shaft 3 at the front end of which is fixed at least one drive wheel 4 provided to set in motion two belts 5a, 5b.

[0070] According to this embodiment, the two belts 5a, 5b are smooth, just like the drive wheel 4; this means that this drive wheel 4 has a smooth axial circumferential surface 15.

[0071] The smooth drive wheel 4 is intended to co-operate with the two belts 5a, 5b which adhere to it in parallel and can, thanks to this, be set in motion by the rotation of the shaft 3 of the motor 2. In this embodiment, the smooth drive wheel 4 has a disengagement groove delimiting two smooth areas intended to receive and retain each of the two belts 5a, 5b axially.

[0072] According to a variant, the drive device 1 comprises a drive shaft 3 at the front end of which is fixed two drive wheels 4 provided to set in motion the two belts 5a, 5b.

[0073] Since the two belts 5a, 5b are also provided to act upon the rotor shafts 9,10 des rotors 7, 8, by making them turn, these rotor shafts 9, 10 have sections whose axial circumferential surfaces are smooth to receive the two belts 5a, 5b in parallel and make them adhere. These smooth sections 16, 17 are thus situated at the front end of the shafts 9, 10 of the rotors 7, 8, and comprise a disengagement groove delimiting two smooth sections for each rotor shaft 9, 10 intended to receive and retain each of the two belts 5a, 5b axially.

[0074] As can be seen in particular in FIG. 5, the two belts 5a, 5b each form in parallel a loop going from the drive wheel 4 to the first rotor shaft, that is to say the rotor shaft 9 farthest from the drive wheel 4. The two belts 5a, 5b thus each rest in parallel on the smooth axial circumferential surface 15 of the drive wheel 4 and the smooth sections 16 of the rotor shaft 9, and they are stretched between this rotor shaft 9 and this drive wheel 4.

[0075] However, in order to be able to also drive the second rotor shaft 10 situated between the first rotor shaft 9 and the drive wheel 4, the two belts 5a, 5b must come into contact with the smooth sections 17 of the second rotor shaft 10 and adhere in parallel thereto. This is achieved by deforming the path of the two belts 5a, 5b which would be trapezoidal if there were only one shaft. Thus, the path of the two belts 5a, 5b is bent by forcing them to pass under the smooth sections 17 of the second rotor shaft 10 (cf. FIGS. 5 and 6).

[0076] The belts 5a, 5b therefore partially surround the wheel 4 of the drive device 1 and the smooth sections 16 of the first rotor shaft 9, and they are pressed downward by the smooth sections 17 of the second rotor shaft 10 (cf. FIG. 6).

[0077] In order to facilitate their driving in rotation, the rotor shafts 9, 10 of the rotors 7, 8 preferably each comprise a discoid part 19, 20, increasing their diameter, the axial circumferential surface of which is smooth and includes a disengagement groove delimiting two smooth zones intended to receive and retain each of the two belts 5a, 5b axially. The discoid parts 19, 20 then constitute the smooth sections 16, 17 of the rotor shaft 9, 10 under consideration (cf. FIG. 7).

[0078] According to a variant, the rotor shafts 9, 10 of the rotors 7, 8 each comprise two discoid parts 19, 20.

[0079] The discoid parts 19, 20 and the drive wheel 4 are substantially in the same plane, so as to be able to cooperate effectively with the two belts 5a, 5b. Their axial thicknesses are generally at least equal to those of the two belts 5a, 5b (cf. FIG. 7).

[0080] In the embodiment represented in FIGS. 6 and 8, the discoid parts 19, 20 comprise bearings 21a, 21b, such as sealed bearings, ball bearings, or deep groove ball bearings.

[0081] Generally the risk of slipping of a belt is a function of the torque and of the grip angle of the belt on the discoid parts. In an advantageous way, according to the second preferred embodiment of the invention, each of the two belts 5a, 5b runs a risk of slipping independently, making it possible to further reduce the work of resynchronization of the toothed wheels. Compensation for the risk of slipping with the aid of two belts 5a, 5b thus makes it possible to decrease and limit the risk of desynchronization of the toothed wheels and their attrition.

[0082] It is evident that the present invention is subject to many variations in its implementation. Although two non-limiting embodiments have been described by way of example, it is well understood that that it is not conceivable to identify exhaustively all the possible variations. It is of course possible to replace a described means with an equivalent means without departing from the scope of the present invention. All these modifications form part of the common knowledge of one skilled in the art in the field of vacuum pumps. In particular, one skilled in the art will easily recognize that the drive device by belt of the present invention can be used in any kind of positive displacement pump employing two rotors driven in rotation, such as, for example, a screw pump or a claw pump, regardless of whether they are lubricated or dry or whether they are single-staged or multi-staged.