Patent Description:
For the correct operation of the vacuum pump, it is necessary to pre-stress the two bearing elements against one another. To this end, the practice is known of providing a screw element, for example an adjusting nut, in order to alter the axial position of the rotor shaft relative to the stator. Through this, the bearing elements are appropriately pre-stressed. This has the disadvantage, however, particularly in the case of high axial rigidity of the bearing elements, that even small changes in the screw position of the adjusting nut lead to a major change in the pre-stress force of the bearing elements.

Because of this, precise adjustment is difficult, and there is a risk of inaccurate adjustment, and furthermore adjustment that is not constant over the duration of operation.

<CIT> discloses an adjusting ring having an adjusting portion for axially aligning a radially inner first bearing portion of a bearing of a vacuum pump in the direction of a longitudinal centre axis of the bearing relative to a radially outer second bearing portion of the bearing of the vacuum pump. A circumferential collar emerges from the adjustment portion of the adjustment ring, which has a radially outwardly extending radial collar portion.

<CIT> discloses a vacuum pump with a stator, a rotor and a permanent magnet bearing for rotatable mounting of the rotor, wherein an adjusting device is provided for adjusting the resonance frequency of the permanent magnet bearing.

The task of the present invention is to create a vacuum pump in which highly precise setting of the bearing pre-stress can be effected in a simple manner.

According to the invention, the problem is solved by a vacuum pump according to claim <NUM>.

The vacuum pump according to the invention, which in particular is a turbomolecular vacuum pump (for short: turbomolecular pump), has a rotor shaft that is borne in a pump housing. The rotor shaft bears at least one rotor element. In the case of the turbomolecular vacuum pump, the rotor shaft bears several rotor disks, which work together with stator disks arranged in alternation to the rotor disks. The stator disks are fixed in the housing. In the case of turbomolecular pumps in particular, the rotor shaft frequently additionally bears a Holweck pump, with the corresponding stator elements once again being connected to the housing. Furthermore, two bearing seat elements are connected to the pump housing, and in particular they are designed as one piece, so that in each case one bearing can be arranged between the two bearing seat elements and the rotor shaft. According to the invention, here at least one bearing has a stationary first magnet element that is connected to the bearing seat element, and a co-rotating second magnet element that is connected to the rotor shaft. Here, the first magnet element and the second magnet element repel one another magnetically, through which a bearing of the rotor shaft is produced. In particular, the magnet elements are permanent magnets, so that through the first magnet element and the second magnet element, a permanent magnet bearing or at least a radial permanent magnet bearing is created.

Here, the first magnet element and the second magnet element respectively have several magnet rings. The magnet rings of the first magnet element respectively surround the magnet rings of the second magnet element or vice versa, and are thus arranged radially to one another. In this respect, the statically arranged magnet rings, i.e. those connected to the bearing seat element, can encompass the magnet rings connected to the rotor shaft or vice versa, wherein in particular here the bearing seat element is designed as a journal that projects in a recess of the rotor shaft. In particular in the case of a repulsive design of the permanent magnet bearing, the magnet rings of the first magnet element and of the second magnet element are arranged such that the north poles of the magnet rings in each case face one another and accordingly the south poles of the magnet elements in each case face one another. Thus in the case of adjacent magnet rings of the first magnet element or of the second magnet element, in each case the same poles are arranged opposite one another.

According to the invention, a spring element is provided between at least two magnet rings of the first magnet element and/or of the second magnet element. Furthermore, the vacuum pump comprises an axial adjusting element for setting the bearing pre-stress, wherein through the adjusting element, the axial position of the first magnet element or of the second magnet element can be adjusted. Through the adjustment of the axial position of the first magnet element or of the second magnet element relative to one another, the pre-stress is set. At the same time, through the adjustment of the axial position, a compression or relief of the spring element between the at least two magnet rings is effected. Through the provision of the spring element, the adjusting element acts only directly on the first magnet ring whose position is changed, and only indirectly via the spring element on the second magnet ring of the same magnet element. Through this, the change in the bearing pre-stress that is produced via the axial adjusting element is reduced.

Whereas in the case of the known prior art, even a small change to the adjusting element produced a major change in the bearing pre-stress, since the respective entire first or second magnet element was displaced axially, according to the present invention only one magnet ring is displaced directly, through which only a small change in the bearing pre-stress is produced. It is thus possible, by providing the spring element, to achieve an exact and precise setting of the bearing pre-stress.

For preference, the second bearing is a rolling bearing. Here, in particular the bearing that is designed as a permanent magnet bearing is arranged on the suction-side end of the vacuum pump, whereas the rolling bearing is arranged at the delivery-side end, in the direction of the outlet. Alternatively, the two bearings are magnet bearings, in particular permanent magnet bearings.

For preference, the spring element is arranged between two magnet rings of the first magnet element. Thus the spring element is stationary and does not co-rotate, through which the requirement of radial rigidity of the spring element is reduced.

For preference, more than one spring element is provided, in particular between three consecutive magnet rings of the first magnet element and/or of the second magnet element. Through this, it is possible to achieve more precise setting of the bearing pre-stress, since the adjusting element acts directly only on the first magnet ring, acts indirectly on the second magnet ring via first spring element, and the change in axial position of the second magnet ring acts indirectly on the third magnet ring via the second spring element. Through this, the position of the individual magnet rings can be adjusted precisely, since a change to the adjusting element leads only to a small change in the axial position of the second magnet ring and of the third magnet ring.

For preference, the spring elements have the same spring constant. Through this, the construction is simplified. Alternatively, the spring elements have different spring constants, wherein the spring constant, in particular starting out from the adjusting element, increases. Through this, the situation is achieved that a change in the axial position of the third magnet ring leads to a lesser change in the axial position of the second magnet ring than is the case where the spring constants are the same.

For preference, the spring element is a disk spring, a spiral spring or an elastic material.

For preference, the axial adjusting element is a helical feed, in particular an adjusting nut. Thus a screw movement of the axial adjusting element is transferred to a change in axial position of the first magnet element and/or of the second magnet element. Here, the precision that can be achieved via the axial adjusting element is determined by the pitch of the screw thread. However, on account of the provision of the spring element according to the invention, a conventional pitch of the helical feed is sufficient in order to enable adequately precise setting of the bearing pre-stress, even in the case of high axial forces between the bearings.

For preference, the axial adjusting element acts on the first magnet element, so that the axial position of the first magnet element can be adjusted via the axial adjusting element. In particular, the first magnet element is the magnet element that has the at least one spring element.

The invention is explained in more detail below, on the basis of a preferred embodiment, with reference to the attached drawings.

The vacuum pump according to the invention has a rotor shaft <NUM>, which is pivoted in a pump housing <NUM> via a suction-side bearing <NUM> and a delivery-side bearing <NUM>. The rotor shaft bears rotor elements, wherein in the case of the design example shown here, these are rotor disks <NUM> of a turbomolecular pump and a rotor <NUM> of a Holweck pump. Stator disks <NUM> work together with the rotor disks <NUM>, and a stator ring <NUM> with a helical groove works together with the rotor of the Holweck pump. Furthermore, an electric motor <NUM> is connected to the rotor shaft for driving.

The suction-side bearing <NUM> is designed as a permanent magnet bearing and has a stationary first magnet element <NUM> as well as a co-rotating second magnet element <NUM>. The first magnet element <NUM> has several stationary magnet rings <NUM>, which are surrounded by outer co-rotating magnet rings <NUM> of the second magnet element <NUM>. Here, the arrangement of the magnet rings <NUM>, <NUM> is, in particular, repulsive. The outer magnet rings <NUM> of the second magnet element <NUM> are arranged in a recess <NUM> of the rotor shaft <NUM>, so that a tubular part <NUM> of the rotor shaft is arranged between the outer magnet rings <NUM> and the rotor disks <NUM>.

Projecting into the recess <NUM> is a journal <NUM>, which bears the first magnet element <NUM> and connects to the housing <NUM>.

The delivery-side bearing element <NUM> is designed as rolling bearings <NUM> which are arranged between a bearing seat element <NUM> and the rotor <NUM>. The rotor <NUM> is pivoted by means of the first bearing <NUM> and the second bearing <NUM>, wherein through the turning of the rotor <NUM> by the electric motor <NUM>, a gaseous medium is transported from an inlet <NUM> to an outlet <NUM>.

Furthermore, provided on the suction-side bearing <NUM> is an adjusting element <NUM>, which is designed as an adjusting nut and which acts on the magnet rings <NUM> of the first magnet element <NUM>. By turning the adjusting element <NUM>, the axial position of at least part of the magnet rings <NUM> of the first magnet element <NUM> is changed. Through this change in axial position, the bearing pre-stress of the delivery-side bearing <NUM> and of the suction-side bearing <NUM> is changed. Here, a spring element <NUM> is arranged between the magnet rings <NUM> of the first magnet element <NUM>. In the design example of <FIG>, three spring elements <NUM> are shown. The present invention is however not limited to the exact quantity of the spring elements <NUM> provided. In particular, just one spring element can be provided.

Through the provision of the spring element <NUM>, the change in axial position produced by the adjusting element <NUM> which acts directly on the first magnet ring <NUM> of the first magnet element <NUM> starting out from the adjusting element <NUM>, acted only indirectly on the second magnet ring <NUM> via the spring element <NUM>. Thus the change in axial position, starting out from the first magnet ring <NUM> to the second magnet ring <NUM> of the first magnet element <NUM>, is reduced. Thus the effect on the bearing pre-stress is reduced, since only the first magnet ring is directly displaced axially by the adjusting element <NUM>.

<FIG> shows a detailed view. Here, the adjusting element <NUM> is shown schematically as an adjusting screw, wherein by turning the adjusting screw <NUM>, the axial position of the first magnet ring <NUM> of the first magnet element <NUM> is altered, according to the arrow <NUM>. Through the change in position, the spring element <NUM> is compressed, so that only the spring force produced by the change in position of the first magnet ring <NUM> acts indirectly via the spring element <NUM> on the other magnet rings of the first magnet element. Through this, the pre-stress force that is produced by the other magnet rings of the first magnet element <NUM> is reduced, so that precise setting of the bearing pre-stress can be achieved.

As is shown in <FIG>, here the magnet rings of the first magnet element and of the second magnet element are arranged to repel, so that the magnet rings of a magnet element <NUM>, <NUM> face one another with the same pole. Furthermore, the magnet rings of the first magnet element <NUM> and of the second magnet element <NUM> repel one another, through which a magnet bearing is achieved.

Shown in <FIG> is a further embodiment, wherein the same or similar elements are indicated with the same reference numbers. In contrast to the embodiment in <FIG>, the embodiment in <FIG> has a first spring element <NUM> and a second spring element <NUM>. A change in axial position of the first magnet ring <NUM> acts only indirectly on the second magnet ring <NUM> via the first spring element <NUM>, and then via the second spring element <NUM> once again indirectly on the third magnet rings <NUM>. A change in axial position of the first magnet ring <NUM> thus leads to only a minimal change in the axial position of the second magnet ring <NUM>, and in particular of the third magnet ring <NUM>, through which the effect on the bearing pre-stress is reduced. Precise setting of the bearing pre-stress is thus ensured. Here, the first spring element <NUM> and the second spring element <NUM> can have the same spring constant.

Claim 1:
Vacuum pump, in particular a turbomolecular vacuum pump, with
a rotor shaft (<NUM>) borne in a pump housing (<NUM>), this shaft bearing at least one rotor element (<NUM>, <NUM>),
two bearings (<NUM>, <NUM>), respectively arranged between a bearing seat element (<NUM>, <NUM>) connected to the pump housing (<NUM>) and the rotor shaft (<NUM>),
wherein at least one bearing (<NUM>) has a first magnet element (<NUM>) connected to the bearing seat element (<NUM>), and a second magnet element (<NUM>) connected to the rotor shaft (<NUM>), wherein the first magnet element (<NUM>) and the second magnet element (<NUM>) repel one another magnetically to bear the rotor shaft (<NUM>),
wherein the first magnet element (<NUM>) and the second magnet element (<NUM>) respectively have several magnet rings (<NUM>, <NUM>), characterized in that a spring element (<NUM>, <NUM>) is provided between at least two magnet rings (<NUM>, <NUM>) of the first magnet element (<NUM>) and/or of the second magnet element (<NUM>),
wherein the vacuum pump furthermore has an axial adjusting element (<NUM>) for setting the bearing pre-stress, wherein through the adjusting element (<NUM>), the axial position of the first magnet element (<NUM>) or of the second magnet element (<NUM>) can be adjusted, wherein the spring element (<NUM>, <NUM>) is compressed or relieved when the axial position is adjusted.