GB2355861A

GB2355861A - Mounting rotor body to shaft in an electric machine

Info

Publication number: GB2355861A
Application number: GB0022103A
Authority: GB
Inventors: Thomas Heese; Markus Heidrich
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-09-14
Filing date: 2000-09-08
Publication date: 2001-05-02
Anticipated expiration: 2020-09-08
Also published as: BR0004166A; CN1201461C; JP2001112199A; GB0022103D0; CN1288279A; GB2355861B; DE19943951A1

Abstract

A rotor (1) for electrical machine, eg a reluctance motor, comprises a shaft (15), rotor body (12) with an even number of poles (5), and a plurality of fixing elements (9). The number of symmetrical distribution fixings (9) equals at least half and may be the same as or twice the pole number and in a with a specific orientation relative to the poles. which ensures a symmetrical magnetic flux path in the rotor (1). Depending on the ratio of poles to fixings, the radial centre line of the fixings align with the poles, bisects the interpole gap or does both. The fixings may be wedges, springs or elements directly formed on the rotor body or shaft eg flats or protrusions.

Description

2355861 ROTOR FOR AN ELECTRICAL MACHINE The present invention relates to a

rotor for an electrical machine, especially a switched reluctance motor.

The principal components of a rotor for an electric machine, especially a switched reluctance motor, are an armature and a shaft. These two components must be connected together in such a manner that transmission of torque from the armature to the shaft is ensured in all operational states. The connection is often achieved by press fitting or by injection moulding of the armature onto the shaft. If this is not sufficient for higher levels of torque or high temperatures, a simple and secure fixing can also be achieved by fixing elements such as adapter springs, wedges or plate springs or by keying surfaces formed on the shaft. This fixing is normally carried out with only one fixing element, which is, for example, disposed under a pole.

Magnetic field flux paths which are asymmetrical with respect to the longitudinal axis of the shaft arise in rotor planes perpendicular to the axis, especially in the case of a switched reluctance motor, as a result of the known arrangements of fixing elements, as in certain positions a flux path is influenced by the fixing element. This is particularly noticeable in the case of machines with two active poles per phase. Unequal flux paths are thus present according to the respective rotor position. This flux change influences inductivity and thereby leads to changes in torque and to a higher torque pulsation factor.

It is known from US-PS 5 365 137 to distribute fixing elements for the rotor uniformly in the circumferential direction of the shaft. However, there is -no indication whether there is a connection between the number of fixing elements and the number of poles and how the fixing elements are to be disposed relative to the poles.

According to the present invention there is provided a rotor for an electric machine, especially a switched reluctance motor, with an armature which has rotor poles in even number, with a shaft and with fixing elements for the fixing of the armature on the shaft, characterised in that a number of the fixing elements corresponds with at least half the rotor pole number.

In one embodiment, the number of the fixing elements corresponds with exactly or twice 2 the number of rotor poles. Preferably, the fixing elements are disposed between the shaft and the armature and are uniformly distributed in circumferential direction around the shaft. In the case of an uneven number of fixing elements a radial centre line of each element preferably forms a radial centre line of the pole, whereas in the case of an even number of fixing elements the radial centre line of each element preferably halves the angle between two directly adjacent poles. Alternatively, in the case of an equal number of fixing elements and poles the radial centre lines of the elements either halve an angle between two directly adjacent poles or form the radial centre lines of the poles. In the case of twice the number of fixing elements by comparison with the number of poles, the radial centre lines, which are directly adjacent in a rotational direction on the shaft, of the elements alternately halve the angle between two directly adjacent poles or form radial centre lines of the poles.

An adapter spring or a plate spring may be used as a fixing element or a wedge may be so used. If so desired, the fixing element may be directly formed on the shaft and/or directly formed on the armature.

A rotor embodying the invention has the advantage that symmetrical flux paths in the rotor may be produced as a result of a simple measure. It can thereby be achieved that the inductance paths are symmetrical and the torque uniform, so that the torque pulsation factor is reduced. It is particularly advantageous to uniformly distribute the fixing elements in circumferential direction. It is also advantageous to orient the fixing elements according to the respective number of fixing elements and rotor pole number in specific positions with respect to the rotor pole position.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which:

Fig. 1 a is a view of a first rotor embodying the invention; Fig. 1 b is a view of a second rotor embodying the invention; Fig. 1c is a view of a third rotor embodying the invention; Fig. ld is a view of a fourth rotor embodying the invention; 3 Fig. 2a is a view of a fifth rotor embodying the invention, together with a stator and diagrammatic illustration of magnetic flux lines in the rotor and stator; Fig. 215 is a view similar to Fig. 2a, but with the rotor turned through 900; Fig. 3 is a view of a sixth rotor embodying the invention; and Fig. 4 is a view of a seventh rotor embodying the invention.

Referring now to the drawings, there is shown in each of Figs. I a to 1c a rotor 1 with an armature 12 having four rotor poles 5 and with a plurality of fixing elements 9 fixing the armature on a shaft 15. The armature 12 is formed as a lamination stack by, for example, coating a plurality of metal plates and fully encloses or fully contacts a shaft 15. The rotor 1 has a longitudinal axis 17, which is also the axis of the shaft 15 and which extends perpendicularly to the drawing plane. The rotor poles 5 are, for example, distributed symmetrically around the axis 17 and each two poles include an angle a.

In order to achieve a symmetrical magnetic flux path in the rotor 1 during the operation of, for example, a switched reluctance motor containing the rotor, two (Figs. la-c), four (Fig. 1 d) or eight (Fig. 1 e) fixing elements 9 can be mounted symmetrically around the shaft 15 in the case of a four-pole rotor. As fixing elements 9 there can be used, for example, clamping connections with tightening (wedges) or entraining connections without tightening (adapter or fit springs).

As an even number (two or four) of fixing elements 9 used, the elements are according to Figs. la to d arranged between the rotor poles 5. A diarnetral line 18 which runs symmetrically through two opposite fixing elements 9 in that case bisects each angle Cc between two directly adjacent rotor poles 5. These two fixing elements 9 in the installed state are radially or point symmetrical with respect to a centre point lying on the longitudinal axis 17. The extent to which each fixing element 9 projects into the armature 12 or shaft 15 is not of significance.

In Fig. la there are shown fixing elements 9 which each protrude beyond the originally round shaft 15. Each fixing element 9 is, for example, formed directly on the shaft 15 and 4 defines a projection 22.

Fig. lb shows a shaft 15 with keying surfaces 26 as fixing elements 9. Each fixing element 9 is formed directly on the shaft 15 by, for example, suitably flattening the originally round shaft. The arrangement and shaping of the keying surfaces 26 is such that they are radially symmetrical with respect to the centre point 17.

Fig. 1c shows a further embodiment in which each fixing element 9 is formed as a combination of the element in Fig. 1 a, namely a projection 22, and that in Fig. I b, namely a keying surface 26. Other crosssectional shapes of the shaft 15 with fixing elements formed directly on the shaft or provided in the form of at least one adapter spring or at least one wedge are equally possible. It remains a precondition that a radial line 18 runs symmetrically through each fixing element 9 and the fixing elements 9 are radially symmetrical with respect to the centre point 17.

Fig. 1 d shows an embodiment with four fixing elements 9. In that case two of the elements 9 project beyond the originally round shaft 15 and the other two elements are recesses 30 in which protrusions of the armature 12 engage. Instead of the recesses 30, keying surfaces 26, for example, can be used. Other combinations of fixing elements are equally possible. In that case it remains a precondition that radial lines 18 run symmetrically through two opposite fixing elements 9 and the fixing elements 9 are radially symmetrical with respect to the centre point 17. It is possible for the fixing elements 9 to be oriented to the rotor poles 5 if the number of elements corresponds with the pole number as in Fig. Ild.

This corresponds to a rotation of the shaft 15 together with the fixing elements of Fig. Ild about the longitudinal axis 17 through 450 with respect to the armature 12. i In the case of a four-pole rotor 1, eight fixing elements 9 ran also be used, as shown in Fig. le. The fixing elements 9, as seen in circumferential direction, are then oriented between two rotor poles 5 and oriented to a rotor pole 5 in alternation.

The fixing elements can also be formed by a plastic deformation of the shaft. Such a form of connection is known from DE 197 55 091 Al, the disclosure of which is hereby incorporated by reference. A protrusion is formed on the shaft surface in the region of an axial surface of the armature. A recess is formed in the shaft surface, by rolling, on the side of the protrusion opposite to an axial surface. The protrusion, which is produced by plastic deformation of the shaft surface, bears directly against the axial surface and thus fixes the armature. The protrusion, which forms the fixing element and which is formed around the entire shaft 15, thus fulfils the conditions of symmetry.

It is not necessary that the protrusion formed by rolling extends around the entire circumference of the shaft. Individual protrusions only have to be appropriately symmetrical to or oriented between the rotor poles.

On the other hand, a complete annular bead can also be produced by, for example, an appropriately shaped peening tool.

Fig. 2a shows the field course for an embodiment of the rotor in the case of a three-phase switched reluctance motor (not shown) with six stator poles 35 and four rotor poles 5. An adapter spring is used as each fixing element 9. Each adapter spring is oriented between two rotor poles 5, as an even number of fixing elements 9 is present. Field lines 38 run through a stator pole 35 into a rotor pole 5, pass around the shaft 15 with the fixing elements 9, leave the armature 12 at the opposite side by way of a rotor pole 5 at that side and run into another stator pole 35. Disposed around the stator poles 35 is a coil 36, which is schematically illustrated only for the stator poles 35 in which the field lines 38 run into and from the rotor poles 5. The field lines do not run through the fixing elements 9, as these are not magnetic and accordingly form a magnetic resistance. A field line path asymmetrical with respective to the axis 17 would be produced at the fixing element location if only one element were to be present. Due to the addition of a second fixing element 9 at the opposite side of the shaft 15, the field line path is symmetrical with respect to the axis 17.

Fig. 2b shows the field path with the rotor 1 rotated through 900. A symmetrical field line path is produced in every position.

Fig. 3 shows an embodiment for a rotor 1 with a larger, even number of rotor poles 5, in particular a rotor with twelve poles for a four-phase switched reluctance motor with sixteen stator poles. The fixing elements 9 are, for example, adapter springs and are each oriented between two directly adjacent rotor poles 5.

Fig. 4 shows a further embodiment for an uneven number of fixing elements 9. In that 6 case, for example, the rotor 1 has ten poles 5 for a six-phase switched reluctance motor with twelve stator poles. The fixing elements 9 are oriented to every second rotor pole 5 in the case of an uneven number. This means that a radial line 18 of symmetry through the fixing element 9 runs symmetrically through the rotor pole 5.

A radial symmetry with respect to the axis of the shaft 15 with the fixing elements 9 as in Figs. 1 a to e does not apply when the number of fixing elements 9 is uneven. In this case, the radial lines 18 must run symmetrically through the one fixing element 9 and the rotor pole 5. If the number of rotor poles 5 divided by two gives an uneven number, but the number of fixing elements 9 corresponds exactly to or is twice the number of rotor poles, the radial symmetry of the fixing elements 9 with respect to the centre point again applies.

If the number of fixing elements 9 corresponds to the number of rotor poles, then all fixing elements 9 can be oriented either to the rotor pole 5 or between two directly adjacent rotor poles 5.

In the case of the rotor 1 according to Fig. 4, twenty fixing elements 9 can be used. In that case, the directly adjacent fixing elements 9, as seen in circumferential direction, are oriented to two directly adjacent rotor poles and to the rotor pole in alternation.

7

Claims

1 A rotor for an electric machine, comprising a shaft, an armature with an even number of poles, and fixing elements fixing the armature to the shaft, the number of fixing elements being equal to at least half the number of poles.

2. A rotor as claimed in claim 1, wherein the number of fixing elements is same as or twice the number of poles.

3. A rotor as claimed in claim 1 or claim 2, wherein the fixing elements are disposed between the shaft and the armature and equidistantly spaced around the shaft.

4. A rotor as claimed in claim 1, wherein the number of fixing elements is uneven and the radial centre line of each element coincides with the radial centre line of a respective one of the poles.

5. A rotor as claimed in claim 1, wherein the number of fixing elements is even and the radial centre line of each eleme nt bisects the angle included by the radial centre lines of a respective pair of directly adjacent poles.

6. A rotor as claimed in claim 1, wherein the number of fixing elements is the same as the number of poles and the radial centre lines of the elements either coincide with the radial centre lines of the poles or bisect the angles included by the centre lines of adjacent pairs of poles.

7. A rotor as claimed in claim 1, wherein the number of fixing elements is twice the number of poles and the radial centre lines of the fixing elements in alternation coincide with the radial centre line of a respective pole and bisect the angle included by the radial centre lines of a respective pair of directly adjacent poles.

8. A rotor as claimed in any one of the preceding claims, wherein at least one of the fixing elements comprises an adapter spring or a plate spring.

9. A rotor as claimed in any one of the preceding claims, wherein at least one of the fixing elements comprises a wedge.

8

10. A rotor as claimed in any one of the preceding claims, wherein at least one of the fixing elements is formed directly on the shaft.

11. A rotor as claimed in any one of the preceding claims, wherein at least one of the fixing elements is formed directly on the armature.

12. A rotor as claimed in any one of the preceding claims, wherein the rotor is for a reluctance motor.

13. A rotor substantially as hereinbefore described with reference to any one of Figs. 1 a to 1 e of the accompanying drawings.

14. A rotor substantially as hereinbefore described with reference to Figs. 2a and 2b of the accompanying drawings.

15. A rotor substantially as hereinbefore described with reference to Fig. 3 or Fig. 4 of the accompanying drawings.

16. An electrical machine comprising a rotor as claimed in any one of the preceding claims.