EP0378163B1 - Gaede-type vacuum pump - Google Patents

Abstract

Pump comprising a stator (1) and a rotor (2) rotationally driven inside the stator, the stator comprising an intake inlet (12) and a delivery outlet (13), characterised in that the rotor, in its working part located between the intake and the delivery, is of semi-spherical shape (9) and is arranged inside a similarly semi-spherical cavity (10) of the rotor, the axis DELTA of the said rotor merging with the axis of the semi-spherical cavity of the stator, the intake occurring on the side of the great circle of the semi-spherical rotor through the radial play (ja) between the rotor and the stator and the delivery on the side of the top of the semi-spherical rotor, an adjusting shim (14) positioning the rotor (2) axially in relation to the stator (1) in such a way that the radial play on the delivery jr is less than the radial play on the intake ja. <IMAGE>

Description

The present invention relates to a vacuum pump of the Gaëde channel type comprising a stator and a rotor driven in rotation inside the stator, the stator comprising a suction inlet and a discharge outlet.

Pumps of this type are well known under the name of Holweck pumps or Gaëde channel pumps. In this type of pump, the rotor has the shape of a disc or a cylinder of revolution or a cone and its surface is provided with at least one helical groove and the surface of the stator facing it, is smooth or so, which is more often the case, it is the opposite, the surface of the rotor being smooth and that of the stator carrying the grooves. Sometimes again, the two facing surfaces carry such grooves. These grooves generally have a depth which decreases in the direction of the suction towards the discharge.

To obtain good performance, it is advantageous to reduce the operating clearance between the rotor and the stator as much as possible, which implies the need to produce the rotor and the stator with very high precision, but it is difficult to obtain a very high form accuracy with known pumps.

German document DE-C-912 007 describes a pump of this type but with a spherical rotor. This is quite interesting because the spherical surfaces can be produced with very high precision greater than a thousandth of a millimeter, by milling with a milling cutter or cup wheel, or by molding, and therefore reducing the operating clearances.

The present invention aims to improve a pump of this type by increasing its compression ratio.

The subject of the invention is therefore a vacuum pump of the gaëde channel type comprising a stator and a rotor driven in rotation inside the stator, the stator comprising a suction inlet and a discharge outlet, characterized in that that said rotor, in its active part situated between the suction and the discharge, consists of two hemispherical parts joined by a cylindrical central part, disposed in a cavity of the rotor also comprising two hemispherical cavities connected by an intermediate portion corresponding to the cylindrical part of the rotor and through which the intake takes place, the center of each hemispherical part of the rotor being offset from the center of the corresponding hemispherical cavity of the stator so that the radial clearance at suction j _a , at the level of the large circle of hemispheres, ie greater than the radial clearance at discharge j _r located, for each hemisphere, in the vicinity of the top of the hemisphere, the axis of rotation of the rotor being coincident with the axis passing through the centers of the two large circles of the hemispherical cavities of the stator.

According to another embodiment, the invention relates to a vacuum pump of the Gaëde channel type comprising a stator and a rotor driven in rotation inside the stator, the stator comprising a suction inlet and a discharge outlet , characterized in that the rotor, in its active part located between the suction and the discharge, has a hemispherical shape and is disposed inside a also hemispherical cavity of the stator, the axis Δ of said rotor being coincident with the axis of the hemispherical cavity of the stator, the suction being done on the side of the large circle of the hemispherical rotor, by the radial clearance between the rotor and the stator and the discharge on the side of the top of the hemispherical rotor, an adjusting shim positioning axially the rotor with respect to the stator so that the radial clearance at the discharge is lower than the radial clearance at the intake.

Advantageously, said shim comprises axial adjustment means so as to adjust the radial clearance between the stator and the rotor, on the side of the exhaust, by axial offset of the rotor relative to the stator.

The wedge is for example movable in rotation and comprises inclined ramps cooperating with balls.

• La figure 1 est une vue schématique en coupe axiale d'une pompe à vide selon l'invention.
• La figure 2 montre un détail d'un aménagement particulier.
• La figure 3 est une vue schématique d'un deuxième mode de réalisation de l'invention.

The invention will now be described with reference to the accompanying drawing in which:

• Figure 1 is a schematic view in axial section of a vacuum pump according to the invention.
• Figure 2 shows a detail of a particular layout.
• Figure 3 is a schematic view of a second embodiment of the invention.

Referring to Figure 1, there is shown a vacuum pump according to the invention comprising a stator 1 and a rotor 2. The rotor 2 comprises a shaft 3 by which it is supported in the stator 1 by means of bearings 4 and 5 The rotor 2 is driven in rotation by means of a motor 6 fixed inside the stator by flanges 7 and 8. The active part of the rotor has a hemispherical shape 9 situated in a cavity 10 also hemispherical of the stator. The axis Δ of the rotor coincides with the axis of the hemispherical cavity of the stator.

, formule dans laquelle R et r sont respectivement les rayons du rotor à l'aspiration et au refoulement et K une constante dépendant de paramètres tels que notamment le rapport $$\frac{{\text{j}}_{\text{r}}}{{\text{j}}_{\text{a}}}$$

. La valeur de K augmentant avec la diminution de ce rapport $$\frac{{\text{j}}_{\text{r}}}{{\text{j}}_{\text{a}}}$$

.On peut par exemple donner à j_a la valeur de 0,1 à 0,2 mm et à j_r environ $$\frac{\text{1}}{\text{100}}$$

mm. On améliore ainsi beaucoup le taux de compression par rapport à une pompe sphérique à jeu constant.The surface of the rotor is hollowed out with a helical groove 11 whose depth is decreasing from the suction 12 located on the side of the large circle of the hemisphere towards the discharge 13 located on the side of the top of the hemisphere. The pump shown in FIG. 1 is a block diagram and in reality there are a plurality of helical grooves 11. These grooves can moreover be produced not on the rotor but in the stator cavity or even possibly on the rotor and also in the stator. As seen in the figure, the center 0 ′ of the rotor is axially offset from the center 0 of the hemispherical cavity of the stator so that the radial clearance at suction j _a is greater than the radial clearance at repression j _r . The precise relative adjustment of these clearances j _r and j _a is carried out by means of a shim 14. This makes it possible to improve the compression ratio which is of the form K $$\frac{\text{R²}}{\text{r²}}$$

, formula in which R and r are respectively the radii of the rotor on suction and discharge and K a constant depending on parameters such as in particular the ratio $$\frac{{\text{j}}_{\text{r}}}{{\text{j}}_{\text{at}}}$$

. The value of K increases with the decrease of this ratio $$\frac{{\text{j}}_{\text{r}}}{{\text{j}}_{\text{at}}}$$

.We may for example give j _has the value of 0.1 to 0.2 mm and approximately _r j $$\frac{\text{1}}{\text{100}}$$

mm. This greatly improves the compression ratio compared to a spherical pump with constant clearance.

The value of K is also increased by decreasing the depth of the helical grooves 11 from the suction to the discharge.

A dynamic groove seal 15 provides dynamic sealing between the stator 10 and the shaft 3 of the rotor 2 downstream of the discharge 13 and upstream of the first bearing 4. An orifice 16 is provided downstream of the dynamic seal.

FIG. 2 is a detail showing an embodiment in which the shim 14 is adjustable, making it possible to vary the clearance at the delivery j _r . In this case, the wedge 14 comprises inclined ramps 17 associated with balls 18 held in a cage 19. The rotation of the wedge, for its adjustment, is carried out by a motor 20.

Figure 3 shows a variant in which the rotor 2 is double and therefore consists of two hemispherical parts 21 and 22 joined by a cylindrical central part 30. Here, there is a double pump, the central part 30 allowing to play the role of decentering of the two hemispherical parts 21 and 22 of the rotor relative to the two hemispherical cavities 31, 32 of the stator. The axis Δ of the rotor coincides with the axis which joins the centers 0 and 0₁ of the two large circles of the hemispherical cavities of the stator. The hemispherical cavities 31 and 32 are joined by an intermediate portion 33 which forms an intake ring. The inlet 23 is located in the middle and the flow is distributed to the right and to the left, the outlets 24 and 25 of the two parts meet at 26. This arrangement makes it possible to approximately double the flow rate of the pump.

As an indication, the following numerical values can be given for a pump corresponding to FIG. 1:
the compression ratio varies from around 25 to 300 depending on the value of the ratio $$\frac{{\text{j}}_{\text{at}}}{{\text{j}}_{\text{r}}}\text{.}$$

The flow is between 0.3 l / s and 2.7 l / s for rotors whose large diameter is between 100 and 300 mm with a rotation speed of 24,000 rpm.

To increase the compression ratio, it is easy to assemble a pump with two compression stages, or more than two stages.

For a two-stage pump, the compression ratio can be up to 9.10⁴.

You can also, to increase the flow rate, provide the rotor with a front wing wheel.

The pump also has the usual advantages of dry pumps.

Claims (4)

1. A vacuum pump of the type having a Gaede channel, the pump comprising a stator (1) and a rotor (2) driven to rotate inside the stator, the stator having a suction inlet (12) and a delivery outlet (13), the pump being characterized in that the active portion of said rotor situated between the suction inlet and the delivery outlet is constituted by two hemispherical portions (21, 22) which are interconnected by a central cylindrical portion (30), the rotor being disposed in a rotor cavity likewise comprising two hemispherical cavities (31, 32) interconnected by an intermediate portion corresponding to the cylindrical portion of the rotor and through which admission takes place, the center of each hemispherical portion of the rotor being offset relative to the center of the corresponding hemispherical cavity of the stator and in such a manner that the radial clearance j_a at the level of the large circles of the hemispheres is greater than the radial clearance j_r at the delivery end situated, for each of the hemispheres, in the vicinity of the top of the hemisphere, with the axis of rotation Δ of the rotor coinciding with the axis passing through the centers (0, 0₁) of the two large circles of the hemispherical cavities in the stator.
2. A vacuum pump of the type having a Gaede channel, the pump comprising a stator (1) and a rotor (2) driven to rotate inside the stator, the stator including a suction inlet (12) and a delivery outlet (13), the pump being characterized in that the active portion of the rotor situated between the suction inlet and the delivery outlet is hemispherical in shape (9) and is disposed inside a cavity (10) of the stator which is likewise hemispherical in shape, the axis Δ of said rotor coinciding with the axis of the hemispherical cavity of the stator, with the suction taking place at the large circle end of the hemispherical rotor via the radial clearance j_a between the rotor and the stator, and the delivery taking place at the top end of the hemispherical rotor, an adjustment distance piece (14) for axially positioning the rotor (2) relative to the stator (1) being provided so that the radial delivery clearance j_r is smaller than the radial suction clearance j_a.
3. A vacuum pump according to claim 2, characterized in that said distance piece (14) includes axial adjustment means (17, 18, 19) to enable the radial clearance (j_r) between the stator and the rotor to be adjusted at the delivery end by varying the axial offset between the center of the rotor and the center of the stator.
4. A vacuum pump according to claim 3, characterized in that said distance piece is rotatable and includes slopes (17) cooperating with balls (18).

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