GB2334629A

GB2334629A - Thrust ring in an electric motor

Info

Publication number: GB2334629A
Application number: GB9901156A
Authority: GB
Inventors: Josef Siraky; Bernhard Wolfle
Original assignee: Max Stegmann GmbH
Current assignee: Sick Stegmann GmbH
Priority date: 1998-01-23
Filing date: 1999-01-19
Publication date: 1999-08-25
Also published as: ITRM980264U1; FR2774226B3; IT245743Y1; FR2774226A3; DE29801110U1; GB9901156D0

Abstract

In an electric motor having a permanent-magnet rotor (16), the shaft (18) is mounted under axial spring pressure in bearings (14) of a casing (10), thrust rings being disposed between the bearings (14) and the rotor (16). At least one thrust ring is formed as a ferromagnetic spring washer (24) whose radially inner hub region (28) is axially up against the bearing (14) and whose radially outer circumferential region (30) is axially up against the rotor (16), the hub region (28) and the circumferential region (30) being joined resiliently to one another.

Description

Electric motor The invention relates to an electric motor having a permanent-magnet rotor.

In electric motors having permanent-magnet rotors, preferably synchronous or stepping motors, the shaft of the rotor is conventionally mounted at both ends by means of bearings.in a casing of the electric motor. In order to mount the rotor in a stably positioned manner, a helical compression spring is mounted on the shaft at one end of the rotor, which helical compression spring rests, on the one hand, on the rotor and, on the other hand, on the bearing. The helical compression spring holds the rotor stably adjacent to the opposite bearing. In order to absorb the axial spring pressure with minimal friction and low wear, thrust rings which are preferably composed of plastic are inserted between the bearings and the rotor or the helical compression spring.

The mounting of the helical compression spring and the thrust springs on the shaft of the rotor is an expensive assembly operation. Furthermore, it is difficult from an assembly engineering point of view to insert the rotor fitted with the helical compression spring and the thrust rings into the bearing of the casing. Automation of the assembly sequences is scarcely possible.

The aim of the invention is to design an electric motor having a permanent-magnet rotor so that the assembly is simplified.

According to the invention, this aim is achieved by an electric motor having a permanent-magnet rotor whose shaft is mounted under axial spring pressure in bearings of a casing, thrust rings being disposed between the bearings and the rotor, wherein at least one thrust ring is formed as a ferromagnetic spring washer whose radially inner hub region is axially up against the bearing and whose radially outer circumferential region is axially up against the rotor, the hub region and the circumferential region being joined resiliently to one another.

Advantageous embodiments of the invention are specified in the dependent claims.

The essential idea of the invention is to generate the spring pressure for the axial positioning of the rotor by ferromagnetic spring washers which take on both the function of generating the axial spring pressure and the function of the thrust rings. This reduces the number of individual parts, which, on the one hand, reduces the production costs and, on the other hand, saves a working step in the assembly. Furthermore, a substantial advantage arises from the fact that the ferromagnetic spring washers are magnetically held against the permanent-magnet rotor after being mounted on the shaft.

The rotor fitted with the spring washers can consequently be inserted into the casing in a problem-free manner without measures being necessary to secure the spring washers during the assembly.

The spring washers are preferably produced as singlepiece punched parts, resulting in an efficient and lowcost manufacture.

An embodiment of the invention is described hereunder, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows an axial section of the electric motor in the individual parts, Figure 2 shows an axial section of the assembled electric motor and Figure 3 shows an embodiment of the spring washer in perspective.

The electric motor has a casing 10 which is made up of two half shells 10a and lob which are specularly symmetrical with respect to a central plane. Poles 12 are broken out of the end faces of the half shells 10a, lOb and bent into the interior of the casing 10 so that an accommodation space for the stator windings is formed between the poles 12 and the external circumference of the casing 10.

Inserted centrally and coaxially in each of the casing half shells 10a, lOb is a bearing 14 which is designed as sliding bearing. A permanent-magnet rotor 16 is mounted on a shaft 18 whose two ends are each mounted in the bearings 14 of the casing 10. The rotor 16 has an external cylindrical sleeve 20 and an internal cylindrical hub 22. The external circumference of the sleeve 20 is internally adjacent to the poles 12 and, consequently, to the stator windings. The shaft 18 is pressed axially into the hub 22. The sleeve 20 and the hub 22 are radially joined to one another. At one end face, at the left-hand end face in the drawing, the sleeve 20 and the hub 22 terminate in a common radial plane. At the other end face, at the right-hand end face in the drawing, the sleeve 20 projects axially over the hub 22, i.e. the hub 22 is offset towards the interior with respect to the end-face rim of the sleeve 20.

Mounted on each of the two ends of the shaft 18 is a spring washer 24 which is punched out of a ferromagnetic sheet. The spring washers 24 have a central bore 26 which accommodates the shaft 18. The bore 26 is surrounded by an internal hub region 28. An outer circumferential region 30 is resiliently joined to the interior hub region 28. During assembly, one spring washer 24 is in each case pushed onto each end of the shaft 18, the ferromagnetic spring washer 24 being magnetically secured by the permanent-magnet rotor 16. The rotor 16 with the magnetically secured spring washers 24 is mounted in the casing 10, for which purpose the two ends of the shaft 18 are inserted into the respective bearing 14. In the assembled state, which is shown in Figure 2, the inner hub region 28 of the spring washer 24 is situated at one side, in the drawing the left-hand side, between the bearing 14 and the hub 22 of the rotor, while the circumferential region 30 of the spring washer 24 is up against the end face of the sleeve 20 of the rotor 16.

The hub 22 of the rotor 16 consequently rests axially on the bearing 14 axially over that hub region 28 of the spring washer 24 which acts as thrust ring. Under these circumstances, the spring washer 24 does not generate a spring action. At the opposite end face, in the drawing the right-hand end face, the inner hub region 28 of the spring washer 24 rests against the bearing 14 while the radially outer circumferential region 30 rests against the end face of the sleeve 20. Since the hub 22 is axially set back on this side with respect to the sleeve 20, the inner hub region 28 of the spring washer 24 is supported by the bearing 14 only from one side, while the outer circumferential region 30 of the opposite side is supported by the sleeve 20 of the rotor 16. The spring washer 24 consequently generates an axial spring action which holds the rotor 16 axially against the opposite bearing 14, in the drawing the left-hand bearing 14.

The spring washers 24 may be formed in varying shapes.

Because of the favourable production costs, the spring washers 24 are preferably manufactured as punched parts from a ferromagnetic metal sheet.

The spring washer 24 is expected to generate only a small axial spring force. The spring force has only to be sufficient to position the rotor 16 axially, i.e. to hold it against the left-hand bearing 14 in the drawing. A greater axial spring force would result only in a disadvantageous increase in the axial pressure and consequently in the friction.

In order to form the spring washers 24 with a soft spring characteristic, the inner hub region 28 is preferably joined to the outer circumferential region 30 only by means of one or a few webs. The webs may extend radially.

Because of the soft spring characteristic a spirally extending web 32 is preferably chosen, as shown in Figure 3.

It is apparent that only the right-hand spring washer 24 in the drawing fulfils per se a spring function and therefore has to be formed as a spring washer. The lefthand spring washer 24 in the drawing may therefore also be formed without spring action and may be formed, in particular, as an annular disc whose external diameter corresponds only to the external diameter of the hub region 28.

Preferably, however, identical spring washers are used at the two axial ends. As a result, it is unnecessary to produce two different shapes of ferromagnetic discs and treat them separately during supply and assembly.

List of reference symbols 10 Casing a/b 12 Pole 14 Bearing 16 Rotor 18 Shaft 20 Sleeve 22 Hub 24 Spring washer 26 Bore 28 Hub region 30 Circumferential region 32 Web

Claims

CLAIMS 1. Electric motor having a permanent-magnet rotor whose shaft is mounted under axial spring pressure in bearings of a casing, thrust rings being disposed between the bearings and the rotor, wherein at least one thrust ring is formed as a ferromagnetic spring washer whose radially inner hub region is axially up against the bearing and whose radially outer circumferential region is axially up against the rotor, the hub region and the circumferential region being joined resiliently to one another.
2. Electric motor according to Claim 1, wherein ferromagnetic spring washers are disposed at the two end faces of the rotor as thrust rings
3. Electric motor according to Claim 2, wherein the spring washers at the two end faces of the rotor are formed with identical shapes.
4. Electric motor according to any one of Claims 1 to 3, wherein the inner hub region and the outer circumferential region of the spring washers are joined to one another by at least one web.
5. Electric motor according to Claim 4, wherein at least two radial webs are provided.
6. Electric motor according to Claim 4, wherein at least one spiral web is provided.
7. Electric motor according to any one of the preceding claims, wherein the spring washers are single-piece metal-sheet punched parts.
8. Electric motor substantially as hereinbefore described with reference to any of Figures 1 to 3 of the accompanying drawings.