EP-4741666-A1 - VACUUM PUMP COMPRISING PERMANENT MAGNETS OF A SYNCHRONOUS MOTOR ARRANGED WITHIN A SHAFT

EP4741666A1EP 4741666 A1EP4741666 A1EP 4741666A1EP-4741666-A1

Abstract

Inventors

Die Erfindernennung liegt noch nicht vor

Assignees

Pfeiffer Vacuum Technology AG

Dates

Publication Date: 20260513
Application Date: 20260317

Claims (15)

Vacuum pump, in particular turbomolecular pump, with a pumping system comprising a stator (11) and a rotor (15) rotating relative to the stator (11) about a rotational axis (13) during operation, and with an electric motor (17) as a rotary drive for the rotor (15), wherein - the electric motor (17) is a permanent magnet synchronous motor, - the rotor (15) comprises a shaft (19), and - the permanent magnets (21) of the synchronous motor (17) are arranged inside the shaft (19).
Vacuum pump according to claim 1, wherein at least one receiving space (23) is formed in the shaft (19) in which the permanent magnets (21) are arranged.
Vacuum pump according to claim 2, wherein the receiving space (23) was created by machining a raw part of the shaft (19), in particular by cutting, in particular by machining.
Vacuum pump according to claim 2 or 3, wherein the receiving space (23) is located between a radially outer sleeve section (25) of the shaft (19) which is concentric to the axis of rotation and a radially inner central section (27), in particular a solid cylinder section, of the shaft (19) which has the axis of rotation (13) as its central axis.
Vacuum pump according to claims 2 to 4, wherein the receiving space (23) is ring-shaped or partially ring-shaped and extends on a circle around the axis of rotation (13).
Vacuum pump according to claims 2 to 5, wherein the recording room (23) comprises a plurality of separate individual rooms which lie on a circle around the axis of rotation (13).
Vacuum pump according to claims 2 to 6, wherein the receiving space (23) is formed by a groove which is formed in a, in particular, flat, end face of the shaft (19) or in an annular surface (29) of the shaft (19) which surrounds a projecting central section (27), in particular a solid cylindrical section.
Vacuum pump according to claims 2 to 7, wherein the permanent magnets (21) are pressed into the receiving space (23).
Vacuum pump according to claims 2 to 8, wherein the receiving chamber (23) is sealed, in particular vacuum-tight.
Vacuum pump according to claims 2 to 9, wherein the receiving chamber (23) is surrounded by an outer wall (25) of the wave.
Vacuum pump according to one of the preceding claims, wherein the permanent magnets (21) are in direct mechanical contact with the material of the shaft (19), in particular with the inner surface (26) of an outer wall (25) that defines the receiving space (23) radially outwards.
Vacuum pump according to one of the preceding claims, wherein the shaft (19) is made of a material which is or comprises aluminium.
Vacuum pump according to one of the preceding claims, wherein the permanent magnets (21) are sintered permanent magnets or plastic-bonded permanent magnets.
Vacuum pump according to one of the preceding claims, wherein the permanent magnets (21) together form a permanent magnet ring that runs around the axis of rotation (13).
Vacuum pump according to one of the preceding claims, where no return component is provided for the permanent magnets (21).

Description

The invention relates to a vacuum pump, in particular a turbomolecular pump, with a pumping system comprising a stator and a rotor rotating about an axis of rotation relative to the stator during operation, and with an electric motor as a rotary drive for the rotor, wherein the electric motor is a permanent magnet synchronous motor. Vacuum pumps with a permanent magnet synchronous motor as the rotary drive for the high-speed rotating rotor are generally known. Such a rotary drive is used particularly, but not exclusively, in turbomolecular pumps. Turbomolecular pumps are vacuum pumps with a fundamentally well-known design and function, offering versatile applications and use in various industrial and scientific environments. The rotor of a vacuum pump can be constructed as a single unit or in multiple parts. In a turbomolecular pump, the rotor includes, among other things, pump-active rotor elements that interact with pump-active stator elements during pumping operation. The pump-active rotor elements and the pump-active stator elements are components of the turbomolecular pump's pumping system. The pump-active rotor elements consist, in particular, of multiple rotor disks, each comprising several rotor blades, which interact with several stator disks, each comprising several stator blades. If the pumping system of the turbomolecular pump includes one or more such turbomolecular pumping stages, one or more Holweck pumping stages If the rotor also includes one or more hollow sleeves that interact with one or more hollow stators of the stator to provide a pumping effect. In many cases, a component of the rotor, also known as the shaft or rotor shaft, simultaneously forms the motor rotor of the electric motor, also referred to as the runner. If the electric motor is a permanent magnet synchronous motor, then its permanent magnets are attached to the motor rotor; that is, the rotor shaft carries the permanent magnets of the permanent magnet synchronous motor. The motor stator of the synchronous motor then includes, among other things, the stator core with the windings, whereby in some designs the stator can comprise several segments, also referred to as teeth, and thus several cores of laminations. In practice, permanent magnets are currently mounted on the outside of the motor rotor. Due to the high rotational speeds of the rotor during operation and the resulting centrifugal forces, the permanent magnets are typically fitted with an outer band, such as a sleeve, to ensure that the magnets remain in their intended radial position during operation. These bands or sleeves are usually made of carbon fiber composites. Additionally, a back iron, also known as a "back iron," such as a backing ring, is often used to improve the magnetic flux distribution of the permanent magnets. It has now been recognized that such a rotor design is disadvantageous, particularly in vacuum applications, due to the different materials used and the resulting differences in mechanical properties. Firstly, such a rotor design with a bandage and return ring is comparatively complex. Furthermore, the bandage, in particular, If the magnets are based on a carbon fiber composite material, this results in thermal insulation of the magnets. Heat generated during operation due to eddy current and hysteresis losses in the magnets can therefore be dissipated poorly or not at all. This can lead to detrimental overheating of the rotor. The purpose of the invention is to eliminate these disadvantages. This problem is solved by the features of independent claim 1. Accordingly, it is provided that the rotor comprises a shaft and the permanent magnets of the synchronous motor are arranged inside the shaft. The arrangement of the permanent magnets inside the rotor shaft represents a departure from the previously used concept of mounting the permanent magnets on the outside of the shaft. It was surprisingly found that the arrangement of the permanent magnets inside the shaft offers several advantages. Firstly, this eliminates the need for an external bandage, as the shaft is mechanically stable enough to hold the permanent magnets in their radial target position inside the shaft despite the centrifugal forces that occur. Secondly, a return ring is no longer required. The magnetic flux can be easily improved by selecting larger permanent magnets, i.e., thicker magnets in the radial direction, which would be problematic with the previously common method of attaching the magnets to the outside of the shaft due to the centrifugal forces occurring during operation. Alternatively, or Additionally, magnets with a suitably chosen remanent flux density can be used to compensate for the missing backplate ring. Furthermore, placing the permanent magnets inside the shaft has the additional advantage that the magnets can be arranged in such a way as to ensure good heat transfer from the magnets to the shaft material. This prevents overheating. Furthermore, it has b