Compressor element for a screw compressor and screw compressor in which such a compressor element is applied

Abstract

A compressor element of a screw compressor inlet side and an outlet side and two helical rotors, respectively a male rotor with a drive for the male rotor and a female rotor that is driven by the male rotor by means of synchronisation gearwheels with at least one synchronisation gearwheel on the male rotor, wherein the drive and synchronisation gearwheels of the male rotor are chosen such that, upon being driven with acceleration of the rotors without gas forces, the resulting mechanical drive force that is exerted by this drive and by this synchronisation gearwheel on the male rotor has an axial component that is directed from the outlet side to the inlet side and that the movement of the male rotor in the axial direction from the outlet side to the inlet side is fixed by means of a single axial single-acting or double-acting bearing.

Claims

1. A compressor element of a screw compressor for compressing gas, with the compressor element comprising: a housing with an inlet for the gas on an inlet side, and an outlet for the gas on an outlet side; and two rotor chambers in which two helical rotors are mounted on bearings that upon being driven mesh together in order to compress the gas, said two helical rotors comprising a male rotor with a drive for rotating the male rotor and a female rotor that is driven by the male rotor by means of synchronisation gearwheels with at least one synchronisation gearwheel on the male rotor and one synchronisation gearwheel on the female rotor, wherein the drive and the synchronisation gearwheels of the male rotor are chosen such that, upon being driven with acceleration of the rotors of the compressor element without gas forces, a resulting mechanical drive force that is exerted by the drive and by the synchronisation gearwheel on the male rotor has an axial component that is directed in an axial direction from the outlet side to the inlet side and that a movement of the male rotor in the axial direction from the outlet side to the inlet side is fixed by means of a single axial single-acting bearing, and wherein the compressor element is an inlet-driven compressor element with the drive of the male rotor on the inlet side of the male rotor and the synchronisation gearwheels on the outlet side of the male rotor and that the single axial bearing of the male rotor is mounted on the outlet side.

2. The compressor element according to claim 1, wherein there are no force-compensating means for the male rotor that are intended to exert a force in an axial direction on the male rotor.

3. The compressor element according to claim 1, wherein the male rotor is radially mounted on bearings by means of two radial bearings, respectively one radial bearing on the inlet side of the rotor and one radial bearing on the outlet side.

4. The compressor element according to claim 1, wherein the drive is such that, when the compressor element is driven, it exerts little or no axial force on the male rotor or an axial force that is directed from the outlet side to the inlet side.

5. The compressor element according to claim 4, wherein the drive on the male rotor comprises a drive gearwheel with an oblique or helical toothing of which a pitch of the oblique or helical toothing is oriented opposite to a pitch of the helix of the male rotor with respect to the axial direction of the male rotor.

6. The compressor element according to claim 1, wherein at least one axial bearing is a bearing with ball-centred cage.

7. The compressor element according to claim 1, wherein at least one axial bearing is a hybrid bearing with ceramic balls.

8. The compressor element according to claim 1, wherein an inlet end face of the housing of the compressor element is formed by a bearing cover that is supported on a machined mounting surface of the housing that also acts as a mounting surface for a housing of the drive.

9. The screw compressor comprising the compressor element according to claim 1 that is driven by means of the drive on the male rotor, whereby the drive exerts a force on the male rotor that has the axial component that is directed from the outlet side to the inlet side of the male rotor or which is equal to zero.

10. A compressor element of a screw compressor for compressing gas, with the compressor element comprising: a housing with an inlet for the gas on an inlet side, and an outlet for the gas on an outlet side; and two rotor chambers in which two helical rotors are mounted on bearings that upon being driven mesh together in order to compress the gas, said two helical rotors comprising a male rotor with a drive for rotating the male rotor and a female rotor that is driven by the male rotor by means of synchronisation gearwheels with at least one synchronisation gearwheel on the male rotor and one synchronisation gearwheel on the female rotor, wherein the drive and the synchronisation gearwheels of the male rotor are chosen such that, upon being driven with acceleration of the rotors of the compressor element without gas forces, a resulting mechanical drive force that is exerted by the drive and by the synchronisation gearwheel on the male rotor has an axial component that is directed in an axial direction from the outlet side to the inlet side and that a movement of the male rotor in the axial direction from the outlet side to the inlet side is fixed by means of a single axial single-acting or double-acting bearing, wherein the synchronisation gearwheel of the male rotor is provided with an oblique or helical toothing, whereby a pitch of the oblique or helical toothing of the synchronisation gearwheel and a pitch of the helix of the male rotor with respect to the axial direction of the male rotor have the same orientation.

11. A compressor element of a screw compressor for compressing gas, with the compressor element comprising: a housing with an inlet for the gas on an inlet side, and an outlet for the gas on an outlet side; and two rotor chambers in which two helical rotors are mounted on bearings that upon being driven mesh together in order to compress the gas, said two helical rotors comprising a male rotor with a drive for rotating the male rotor and a female rotor that is driven by the male rotor by means of synchronisation gearwheels with at least one synchronisation gearwheel on the male rotor and one synchronisation gearwheel on the female rotor, wherein the drive and the synchronisation gearwheels of the male rotor are chosen such that, upon being driven with acceleration of the rotors of the compressor element without gas forces, a resulting mechanical drive force that is exerted by the drive and by the synchronisation gearwheel on the male rotor has an axial component that is directed in an axial direction from the outlet side to the inlet side and that a movement of the male rotor in the axial direction from the outlet side to the inlet side is fixed by means of a single axial single-acting or double-acting bearing, wherein the female rotor is mounted on axial bearings in the housing by means of two axial bearings that are both mounted on the outlet side of the female rotor and which together block the female rotor in the axial direction, both from the inlet side to the outlet side and from the outlet side to the inlet side.

12. The compressor element according to claim 11, wherein the axial bearings are mounted on either side of the synchronisation gearwheel of the female rotor.

13. The compressor element according to claim 12, wherein at least one of the two axial bearings is placed under an axial prestress that exerts a prestress force that is directed from the outlet side to the inlet side.

14. The compressor element according to claim 13, wherein a prestress is only exerted on the outermost bearing of the two axial bearings by means of a spring that is tightened between this outermost axial bearing and the housing of the compressor element.

15. The compressor element according to claim 13, wherein a flexible spring is used for the prestress spring whose built-in length/rotor length ratio is greater than 8%, with the rotor length being defined as an axial length of the helical section of the rotor.

16. The compressor element according to claim 11, wherein the female rotor is additionally mounted on bearings by means of two radial bearings, one on the inlet side and one on the outlet side of the female rotor.

17. A compressor element of a screw compressor for compressing gas, with the compressor element comprising: a housing with an inlet for the gas on an inlet side and an outlet for the gas on an outlet side; and two rotor chambers in which two helical rotors are mounted on bearings, which when driven mesh together to compress the gas, said two helical rotors comprising a male rotor with a drive for rotating the male rotor and a female rotor that is driven by the male rotor by means of synchronisation gearwheels with at least one synchronisation gearwheel on the male rotor and one synchronisation gearwheel on the female rotor, wherein the compressor element is an inlet-driven compressor element with the drive of the male rotor on the inlet side of the male rotor and the synchronisation gearwheels on the outlet side of the male rotor and that the male rotor is mounted on bearings so that movement of the male rotor in an axial direction from the outlet side to the inlet side is axially fixed by only one single axial bearing that is mounted on the outlet side.

18. The screw compressor comprising the compressor element according to claim 17 that is driven by means of the drive on the male rotor, whereby the drive exerts a force on the male rotor that has the axial component that is directed from the outlet side to the inlet side of the male rotor or which is equal to zero.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) With the intention of better showing the characteristics of the invention, a few preferred embodiments of a screw compressor with a compressor element according to the invention are described hereinafter by way of an example, without any limiting nature, with reference to the accompanying drawings, wherein:

(2) FIG. 1 schematically shows a cross-section of a part of a screw compressor with a compressor element according to the invention;

(3) FIG. 2 shows a cross-section such as that of FIG. 1, but for a variant embodiment.

DETAILED DESCRIPTION OF THE INVENTION

(4) The screw compressor 1 shown in FIG. 1 comprises a compressor element 2 and a drive in the form of a gearwheel transmission 3, of which only a part is shown for reasons of clarity.

(5) The compressor element 2 is provided with a housing 4 with a central section 4a in which two overlapping cylindrical rotor chambers 5 are provided, in which two rotors 6 and 7 are affixed with helical lobes 8, respectively a male rotor 6 and a female rotor 7 whose lobes 8 mesh together in such a way that chambers are separated between the rotors 6 and 7 which, when the compressor element 2 is driven, move in a known way from an inlet, not shown in the drawings, on the inlet side 9 of the rotors 6 and 7 to an outlet 10 on the outlet side 11 of the rotors 6 and 7, whereby during this movement the enclosed gas is compressed.

(6) The axis lines X-X and Y-Y of the two rotors 6 and 7 are arranged practically parallel to one another and are held in an axial direction by their respective end faces 6a and 6b and 7a and 7b, between an inlet end face 12 of the housing 4 that is formed by a bearing cover 4b that forms part of the housing 4 and an outlet end face 13 that in this case is worked directly in the central section 4a of the housing 4.

(7) The male rotor 6 is provided with two coaxial axle journals 6c and 6d by which this rotor 6 is rotatably mounted on bearings in the housing 4, respectively by means of a single radial bearing 14 in the bearing cover 4b on the inlet side 9 of the rotor 6 and by means of one radial bearing 15 and one single axial bearing 16 on the outlet side 11, whereby in the case of FIG. 1 this axial bearing 16 is a single-acting bearing by which the rotor 6 is axially fixed to prevent the male rotor 6 being able to be pushed by its end face 6a on the inlet side 9 against the inlet end face 12 of the housing 4 due to the forces occurring during the operation of the screw compressor 1.

(8) The female rotor 7 is also provided with two end faces 7a and 7b and with two coaxial axle journals 7c and 7d, of which the axle journal 7c on the inlet side 9 of the rotor 7 is mounted on bearings by means of one single radial bearing 17, while the other axial journal 7d is provided with a radial bearing 18 and two axial bearings 19 and 20.

(9) The housing 4 is provided on the outlet side 11 with a cover 4c that is fastened to the central section 4a of the housing 4 and under which the bearings 15, 16, 18, 19 and 20 are protected.

(10) Gaskets 21 are affixed between the various parts 4a, 4b and 4c of the housing 4.

(11) It is specific to the invention that the compressor element 2 is an inlet-driven compressor element, which means that the external gearwheel transmission 3 of the compressor element 2 is on the inlet side 9 and not on the outlet side as is usual.

(12) In the example shown, this gearwheel transmission 3 is schematically shown as a gearwheel transmission of which only a part 3a of the housing is shown and as two gearwheels 22-23 with oblique toothing that mesh together and of which one gearwheel 23, the drive gearwheel, is fastened directly to the axle journal 6c of the male rotor 6. The drive gearwheel 23 can be seen as forming part of the compressor element 2 or as forming part of the gearwheel transmission 3.

(13) The female rotor 7 is driven by the male rotor 6 by means of synchronisation gearwheels on the outlet side 11, in this case two synchronisation gearwheels 24 and 25 with oblique toothing that mesh together and of which one gearwheel 24 is fastened to the axle journal 6d of the male rotor 6 and the other gearwheel 25 on the axle journal 7d of the female rotor 7. The transmission ratio is chosen such that the male rotor 6 drives the female rotor 7 at a lower speed.

(14) The synchronisation gearwheels 24-25 are protected from the environment by means of the aforementioned cover 4c.

(15) The synchronisation gearwheel 25 of the female rotor 7 is flanked by the aforementioned axial bearings 19 and 20 of the female rotor 7, whereby these bearings 19 and 20 are thus each on a different side of this synchronisation gearwheel 25.

(16) On the bearing 20 most oriented towards the outside of these two axial bearings 19 and 20, an axial prestress is exerted by means of a spring 26 that is tightened between the bearing 20 concerned and the cover 4c.

(17) This spring 26 is preferably a flexible spring whose length changes have little effect on the prestress force exerted.

(18) Flexible spring means a spring whose built-in length to rotor length ratio is greater than 8%, with the rotor length L being defined as the axial length of the helical section of the rotor or in other words the axial distance between the end faces of a rotor concerned.

(19) As is usual the rotors 6 and 7 are sealed by means of seals 27. According to a particular aspect of the invention, the choice of an inlet-driven compressor element 2 enables the central section 4a of the housing 4 on the inlet side 9 to be provided with one single machined surface 28, that acts both as a mounting surface 28 for the bearing cover 4b on the inlet side 9 and acts as a mounting surface 28 for the housing 3a of the gearwheel transmission 3, e.g., the drive, which facilitates the axial alignment between the two housings 4 and 3a.

(20) The central section 4a of the housing of the compressor element 2 is provided with a cooling jacket 29 with an inlet 30, which in the case of FIG. 1 connects to an internal cooling channel 31 of the gearwheel transmission 3, whereby this connection is sealed by a simple O-ring 32.

(21) The operation of the device 1 is very simple and as follows.

(22) When the compressor element 1 is driven in the direction of rotation shown by the arrows R in FIG. 1, gas is drawn in a known way due to the meshing of the rotors 6 and 7 via the inlet of the compressor element 2 and after compression is pushed away via the outlet 10.

(23) As a result of the compression, the male rotor 6 and the female rotor 7 experience a gas force with an axial component Fg and Fg that is directed from the outlet side 11 where a higher pressure prevails to the inlet side 9 where a lower pressure prevails.

(24) Furthermore, the rotors 6 and 7 experience forces that are due to the mechanical drive forces that are exerted on the rotors 6 and 7 by the gearwheels 23, 24 and 25, more in particular forces with an axial component Fp and Fs that are exerted respectively by the drive gearwheel 23 and the synchronisation gearwheel 24 on the male rotor 6 and the axial force Fs that is exerted by the other synchronisation gearwheel 25 on the female rotor 7, both in the case of a start-up disregarding the effect of the gas forces, in other words in hypothetical circumstances whereby the rotors 6 and 7 are accelerated without a pressure build-up and thus without gas forces, for example in the event of the rotor chamber 5 of the housing 4 of the compressor element 2 being opened.

(25) According to the invention, the course of the oblique toothing of the oblique gearwheels 23 and 24 of the male rotor 6 are chosen such that the axial forces Fp and Fs act in the same direction as the aforementioned axial gas force Fg, so that the male rotor 6 only experiences forces that tend to push the rotor 6 in the direction of the inlet side 9.

(26) The axial bearing 16 of the male rotor 6 thereby prevents the end face 6a of the male rotor 6 being able to come into contact with the inlet end face 12 of the housing 4 without other means being necessary to this end in the form of a spring, plunger or other compensation means.

(27) In order to bring this about, in FIG. 1 an oblique toothing is chosen whereby the course of the helix of the drive gearwheel 23 and the helix of the male rotor 6 with respect to the axial direction X-X of the male rotor 6 are oriented in opposite directions, while the course of the helix of the synchronisation gearwheel 24 and the helix of the male rotor 6 have the same orientation with respect to the axial direction X-X of the male rotor 6. In other words, this means that when the smallest included angle A measured from the axial direction X-X to the tangential direction of the helical lobes 8 of the male rotor 6 is positive, or in other words oriented in the clockwise direction, and that the smallest included angle B measured from the axial direction X-X to the oblique toothing of the synchronisation gearwheel 24 is positive, or in other words also oriented in the clockwise direction, while the included angle C measured from the axial direction X-X to the oblique toothing of the drive gearwheel 23 is negative, or thus oriented in the anticlockwise direction.

(28) Of course the synchronisation gearwheel 25 of the female rotor 7 presents a toothing that is complementary to that of the synchronisation gearwheel 24 of the male rotor 6, from which it follows that the axial force Fs exerted on the female rotor 7 by the synchronisation gearwheel 25 is opposite to the axial gas force Fg exerted on the female rotor 7 when the screw compressor 1 runs under a load.

(29) Furthermore, the female rotor 7 experiences an axial force Fv as a result of the prestress of the spring 26 that is directed opposite to the force Fs of the synchronisation gearwheel 25 and which is chosen such that in the unloaded state the gas force Fg is eliminated, the prestress force Fv at least compensates the remaining force Fs.

(30) It is clear that the cover 4c on the outlet side 11 is easily detachable, such that all axial bearings 16, 19 and 20, as well as the radial bearings 15 and 18 and the synchronisation gearwheels 24 and 25 and the prestress spring 26 are easily accessible for assembly and/or inspection.

(31) The thickness H and the mass of the bearing cover 4b on the inlet side 9 is relatively limited, as only two radial bearings 14 and 17 have to be accommodated. Moreover, this bearing cover 4b is mounted in the housing 3a of the gearwheel transmission 3, which means a saving of the axial length of the screw compressor 1 compared to existing screw compressors with a similar capacity.

(32) In the event of a leak at the location of the O-ring 32 there is only a risk of coolant leaking into the gearwheel transmission, such that the oil of this gearwheel transmission can be spoiled, but which is less catastrophic than when a leak occurs in the same place in the known compressor elements, whereby in such a case coolant could penetrate into the rotor chambers 5 of the compressor element 2, resulting in the immediate stoppage of the compressor element 2.

(33) For the same reason, no seals are provided between the cooling channel 30 and the cover 4b. Any openings that are needed to realise the cooling channels in the cast cooling jacket 29 are sealed between the cooling jacket 29 and the cover 4c. The seal 33 in FIG. 1 is an example of this. FIG. 2 shows a variant of a compressor element 2 according to the invention, whereby in this case the change of the pitch of the helix of the male rotor 6 is oriented in the opposite direction to a left-handed helix instead of the right-handed helix of the male rotor 6 of FIG. 1.

(34) The course of the direction of the oblique toothing of the drive gearwheel 23 and the synchronisation gearwheels 24 and 25 are in this case opposite to ensure that all forces Fp, fs and Fg that are exerted on the male rotor 6 are oriented from the outlet side 11 to the inlet side 9.

(35) It goes without saying that instead of gearwheels 22 to 25 with oblique toothing, helical or straight gearwheels or other forms of direct or indirect drive can be applied, which when driven are able to exert an axial force on the rotors 6 and 7 or which, if applicable, exert an axial force on the male rotor that is small or even zero. The axial bearings 16, 19 and 20 can be single-acting or double-acting, but the single-acting bearings offer the advantage of being more efficient. The axial bearings can also be a bearing with ball-centered cage.

(36) It is clear that an inlet-driven compressor element 2 offers certain advantages with respect to the conventional outlet-driven compressor elements and that this aspect can also be applied independently, separate from the other characteristics that are included in the description.

(37) It is clear that a number of axial and radial bearings can be applied other than those described above, but that this can bring about extra losses.

(38) It is also clear that the prestress force Fv can also be realised by other means than a spring 26, for example by magnetic interaction or with a plunger. It is not excluded that there are intermediate gearwheels between the synchronisation gearwheels 24 and 25 of the male rotor 6 and of the female rotor 7 for the drive of the female rotor by the male rotor.

(39) In the discussion of the forces account was only taken of the axial component of the exerted forces, although a radial component is also possible. The term force or axial force thus always means the axial component of the force concerned.

(40) The present invention is by no means limited to the embodiments described as an example and shown in the drawings, but a compressor element and screw compressor according to the invention can be realised in all kinds of forms and dimensions without departing from the scope of the invention.