Vacuum pump having fastening element for securing rotor part to rotor shaft and deformed safety element projecting in axial direction for preventing relative rotation between the rotor part and rotor shaft

A vacuum pump has a rotor mounted on a rotor shaft and provided with pump active components cooperating with opposite stationary pump active components, fastening element for securing the rotor on the rotor shaft, and a safety element provided in addition to the fastening element for preventing rotation of the rotor and the rotor shaft relative to each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vacuum pump.

2. Description of the Prior Art

State of the Art (DE 20 2005 019 644 U1) discloses a vacuum pump, e.g., a turbomolecular pump having a rotor with rotatable pump active components and mounted on a rotor shaft. The rotatable pump active components cooperate with stationary pump active components, so-called stator.

The above-mentioned state of the art discloses securing of a bell-shaped rotor to an end side of a rotor shaft with a screw. To this end, the rotor shaft is provided with a recess in which the rotor journal engages.

The drawback of the embodiment disclosed in the state of the art consists in that the rotor can rotate relative to the rotor shaft because the connection of the rotor with the rotor shaft is essentially based on a frictional connection. Because of this, a relative rotation can occur in case of overload. The overload leads to loosening of the connection so that the security of the screw connection is not insured.

Loosening of the rotor during operation leads to a total damage of the pump. Prior art (WO 2012/077411 A1) discloses means for preventing rotation of the rotor. According to this state of the art, there is provided a formlocking connection at which the rotor is secured to the end side of the rotor shaft with several screws. This prevents rotation of the rotor relative to the rotor shaft and, thus, disengagement of the rotor from the rotor shaft. However, the drawback of this state-of-the-art embodiment consists in that the mounting of the rotor is rather expensive and a number of high-cost components, screws, is necessary which make the pump more costly.

The object of the invention is to provide a vacuum pump in which the above-discussed drawbacks of the prior art solutions are absent.

SUMMARY OF THE INVENTION

This and other objects of the invention which will become apparent hereinafter are achieved by providing a vacuum pump having at least one gas inlet opening, at least one gas outlet opening, at least one rotor shaft, a rotor mounted on the at least one rotor shaft and having rotatable therewith pump active components arranged opposite stationary pump active components, at least one fastening element extending in an axial direction and provided in or on the rotor shaft for securing the rotor on the rotor shaft, and at least one safety element provided in addition to the at least one element for preventing rotation of the at least one rotor and the at least one rotor shaft relative to each other.

The relative rotation-preventing safety element can be easily designed and formed, thus, providing a cost-effective solution of preventing rotation of the rotor relative to the rotor shaft and, thereby, loosening of at least one axially extending fastening element provided in or on the rotor shaft.

According to a particularly advantageous embodiment of the present invention, the safety element is provided on the centering journal of the rotor. The centering journal is easily accessible for the centrally arranged fastening element during mounting of the rotor, so that the arrangement of the safety element in the centering journal makes sense.

Basically, there also exists a possibility to provide the centering journal on the rotor shaft so that it would engage in a bore formed in the rotor.

When the centering journal is provided on the rotor, it engages in a corresponding opening of the rotor shaft.

There also exists a possibility that no journal is provided on the rotor and the rotor shaft. In this case, centering can be effected with one or several eccentric shaped elements such as register pins or combined shaped and fastening elements such as close-tolerance screws.

According to a particularly advantageous embodiment of the present invention, the safety element is formed as at least one pin engaging through or in the rotor shaft and through or in the rotor.

Such a pin can be very cost-effectively formed. In addition, the pin need not meet high requirements to the fitting precision, because the rotation of the rotor relative to the rotor shaft is prevented even if the pin retains the rotor shaft and the rotor with a clearance in some positions.

There exists a possibility to arrange the pin radially or axially. Basically, there exists also a possibility to arrange the pin radially inclined.

According to a further advantageous embodiment of the present invention, the pin is arranged in a groove or a bore formed in the centering journal of the rotor. The pin engages with one of its ends in the groove or the bore of the rotor and with another end in the groove or the bore of the rotor shaft.

According to a further advantageous embodiment of the present invention, the safety element is formed as a friction ring. The friction ring has, as a result of selection of an appropriate material and/or a corresponding surface coating, a higher friction coefficient in comparison with rotor and stator components, higher than the friction coefficient which is directly achieved between respective surfaces of the rotor and the rotor shaft. The friction ring is arranged between the rotor and the rotor shaft, preferably between the end surface of the rotor shaft and the surface of the centering journal of the rotor facing the end surface of the rotor shaft. This embodiment insures that the relative rotation between the rotor and the rotor shaft is prevented, without the need to structurally change the rotor or the rotor shaft.

According to a still another advantageous embodiment of the present invention, for increasing the friction coefficient, a coating layer is provided on one or both of connection or bearing surfaces of the rotor and the rotor shaft. With this embodiment, it is possible to prevent a relative rotation between the rotor and the rotor shaft, without using a friction ring.

Basically, there exists a possibility to use both the friction ring and providing a coating on one or both connection or bearing surfaces of the rotor and the rotor shaft.

A yet another advantageous embodiment of the present invention provides a projection in one of the cooperating contact surfaces of the rotor and the rotor shaft and that forms a plastic deformation in an opposite of the contact surfaces of the rotor and the rotor shaft, with the plastic deformation defining a counter-projection.

Such a projection can be formed, e.g., as a so-called punch mark. This punch mark can be formed, e.g., of a rotor material. When the rotor is pressed against the rotor shaft, upon tightening of the fastening element, e.g., a screw, the punch mark plastically deforms the adjacent surface. When the punch mark is provided in the rotor, it plastically deforms the rotor shaft. It is also possible to provide a punch mark in the rotor shaft. Then, the punch mark plastically deforms the rotor. Formation one or several punch marks is advantageous when the rotor and the rotor shaft are formed of different materials. In this case, the punch mark is formed in a material having a greater strength, i.e., a high yield stress Re. In this case, the punch mark is pressed in a softer material.

According to a still further advantageous embodiment of the invention, a radially extending projection is provided in the rotor or the rotor shaft, and a recess for formlockingly receiving the projection is provided in another of the rotor and the rotor shaft.

There is also exists, e.g., a possibility to provide a radial circular elevation having different heights on the end surface of the rotor shaft. A corresponding counter-recess is then provided on the rotor in which the elevation is received. This likewise prevents relative rotation between the rotor and the rotor shaft.

According to a further embodiment, a projection extending in the radial direction is provided in the rotor shaft or the rotor, and in another of the rotor and the rotor shaft, a recess for formlockingly receiving the projection is provided. In this embodiment, it is contemplated, e.g., to provide a projecting nose on the centering journal of the rotor and which is received in a groove in the rotor shaft. The groove defines a stop for the nose, so that the relative rotation of the rotor and the rotor shaft is prevented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a cross-sectional view of a turbomolecular pump according to the state of the art. In the pump, a shaft232, which is located in the pump housing260, is surrounded by a safety bearing295, a radial bearing coil291, a radial sensor293, and a motor coil261. The motor coil261cooperates with a motor magnet262secured on the shaft232with a sleeve263, so that upon energizing the motor coil261, the shaft232rotates with a greater speed. The radial sensor292cooperates with a shaft-side radial sensor target294.

The turbomolecular pump stationary structure is formed of a Holweck stator228located adjacent to fore-vacuum and in which helix-shape channels extend that cooperate with a sleeve227arranged on the rotor, with the Holweck stator228and the sleeve227forming a Holweck stage226.

Further stationary structures are formed by stator discs212,216,220and224which are provided with blade rings and which are axially spaced from each other by spacer rings213,217,221, and225. In the axial intermediate spaces between the stator disc212,216,220and224, pump structures which are formed as rotor blades211,215,219and223extend. Stationary and rotor-side pump structures cooperate in pairs. The rotor blade211and the stator disc212form together a first pump stage210adjacent to the chamber and operating in high vacuum. Correspondingly, the stator disc216and the rotor blade215form the following second stage214, the stator disc220and the rotor blade219from the third stage, and, finally, the stator disc224and the rotor blade223form the fourth stage222that provides for transmission of pressure to the Holweck stage228. The blades are located in spaced from each other, planes250,251,252, and253, with the plane254forming the connection region of the rotor sleeve.

The rotor-side pump structures in form of rotor blades219and223are provided on the first rotor part201and form therewith a one-piece body. The rotor Holweck sleeve is connected with the first rotor part201. The first rotor part201has a recess230in its center. The recess forms a hollow space extending radially and axially from the center, and receives, at least partially, the safety bearing295.

The first rotor part201is connected to the end side258of the rotor shaft232by a fastening element, e.g., a screw280. The shaft232has a recess in which a journal289of the first rotor part201engages. This simplifies the radial positioning. The first rotor part201has, in the embodiment shown in the drawing, a retaining section201athat extends axially from the first rotor part201in the high-vacuum direction, i.e., in the direction remote from the rotor shaft232. A retaining ring208is arranged on the retaining section201a. The rotor blade211is connected with the retaining ring208. A further retaining ring209and the rotor blade215are likewise connected with each other. The retaining rings with rotor blades are conveniently formed.

Balancing boreholes270, in which balancing weights271can be inserted, are provided in the end side retaining section201a. In the rotor blades219and223, also balancing bores272can be provided in which balancing weights273can be arranged

In order to prevent rotation of the first rotor part201relative to the shaft232, a pin281is used as a rotation preventing or safety element and has one of its ends secured in the first rotor part201and the other of its ends secured in the shaft232. Because the pin281is radially spaced from the centrally located screw280, it prevents rotation of the first part201relative to the shaft232.

FIG. 2shows the rotor shaft232on which the rotor part201is secured with the screw280. The pin281prevents rotation of the rotor part201relative to the rotor shaft232.

According toFIG. 2b, an axial bore300is formed in the central journal289. In the shaft232, likewise, a bore301is formed. The pin281, not shown inFIG. 2b, engages with its opposite ends in the bores300and301.

FIGS. 3aand 3bshow the rotor shaft232in which again the bore301is formed. The centering journal289of the rotor part201has, instead of a bore, a groove302. The pin281has one of its ends arranged in the bore301of the rotor shaft232, and has the other of its ends arranged in the groove302of the centering journal289.

The advantage of the embodiment with the groove302in comparison with the embodiment with a bore consists in that the groove302permits to build a statically determined fit system, without maintaining precise tolerances. The radial centering of the rotor part201and the rotor shaft232is effected with the centering journal289. Two further bores with a pin, which must be aligned, would negatively influence this solution because of available tolerances and plays.

The groove302insures that the pin281alone provides for the rotatory degree of freedom, while both radial degrees of freedom, which are insured by the centering journal289, are not influenced.

According toFIGS. 4aand 4b, the pin281is arranged in the groove303of the centering journal289of the rotor part201with a radial inclination and extends into a radial bore304of the shaft232.

In this embodiment, the pin281is secured by a centrifugal force.

According toFIGS. 5aand 5b, the pin281is arranged in the bore305of the rotor part201so that it is radially spaced from the region of the centering journal289. A corresponding counter-bore306is provided in the shaft232. The bore305is provided in the rotor part201in contact with the bearing surface of the shaft232.

FIGS. 6aand 6bshow a further embodiment. The pin281extends radially into the rotor centering journal289, being arranged in the bore307of the centering journal289. The other end of the pin281engages in a groove308in the shaft232.

Another embodiment is shown inFIGS. 7aand 7b. In this embodiment, a friction ring309is provided between the centering journal289and the end side258of the shaft232. The screw280presses the rotor part201to the shaft232. The friction ring309prevents rotation of the rotor part201relative to the shaft232.

According to the embodiment shown inFIGS. 8aand 8b, a punch mark311is provided on the contact surface310of the shaft232. The punch mark lies on the contact surface312of the rotor part201. The shaft232is formed of a stronger material than the rotor part201. When the rotor part201is connected with the shaft232by the screw280, the punch mark311plastically deforms the contact surface312of the rotor part201. The interlocking of the punch mark311with the deformed contact surface provides a form-locking connection that prevents the rotation of the rotor part201relative to the shaft232. It is possible to provide several punch marks.

According toFIGS. 9aand 9b, the shaft232, has, as its end, a deformed geometrical safety element313projecting in the axial direction, with its counter-part314being provided in the rotor part201. The projecting in the axial direction, deformed geometrical safety element313has two elevations315a,316bengaging in corresponding indentations316a,316b. The formlocking connection of elements313and314prevents relative rotation between the rotor part201and the rotor shaft232.

A still further embodiment of the present invention is shown inFIGS. 10aand 10b. In this embodiment, the centering journal289has an extending in the radial direction, deformed projection317arranged in a groove318of the rotor shaft232.

In the groove318of the rotor shaft232, there is provided a stop (not shown), whereby rotation of the rotor part201relative to the shaft232is prevented.

It is possible to combine the embodiments shown inFIGS. 1 through 10with each other.