GB2260862A

GB2260862A - Reduce eddy currents in a laminated alternator core

Info

Publication number: GB2260862A
Application number: GB9222307A
Authority: GB
Inventors: Uwe Kirberg; Jaroslav Moravek; Istvan Ragaly; Helmut Olbertz
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1991-10-25
Filing date: 1992-10-23
Publication date: 1993-04-28
Anticipated expiration: 2012-10-23
Also published as: GB2260862B; ES2040666B1; ES2040666R; GB9222307D0; DE4135207A1; ES2040666A2

Abstract

An alternator for motor vehicles having a claw-pole rotor whose stator (18) has a coated laminated core (15) which comprises thin sheet metal laminae (23, 23a). In order to reduce the eddy current losses in the stator laminated core (15), the thin sheet metal laminae (23) are not insulated in the outer regions and are electrically insulated from each other in the central region (23a) by means of an insulating layer (24). Laminae 23 radially extend beyond the stack and have apertures for receiving screws to centre the core on the alternator housing. <IMAGE>

Description

-1DESCRIPTION ALTERNATOR

The invention relates to an alternator.

In alternators of a claw-pole design for motor vehicles, the stator winding of the alternator is disposed in the grooves of a coated laminated core comprising thin sheet metal laminae. The magnetic potential is produced by means of the excitation winding of the claw-pole rotor and the magnetic flux exits at the claw poles of one of the claw- pole discs, penetrates the stator laminated core by way of the working air gap and then enters again by way of the working air gap at the claw- poles of the other clawpole disc. The electromotive force is, by means of the rotating claw-pole system, induced in the stator windings by means of the alternating flux thereby occurring. The coating of the thin sheet metal laminae of the laminated core according to DE 37 04 157 limits the eddy current losses in the stator of the machine. It is moreover known to further reduce the eddy current losses by applying an insulating layer to the thin metal sheet laminae. However, this produces additional expenditure in both labour and material and the structural length of the laminated core is undesirably increased, with the result that the clawpole rotor is of a correspondingly longer design.

It is an object of the present invention to reduce the eddy current losses for alternators of this type with a saving in labour and material costs.

In accordance with the present invention there is provided an alternator having a claw-pole rotor, a coated laminated core comprising thin sheet metal laminae, a stator, whose stator winding is disposed in grooves of the laminae, wherein, in order to limit the axial eddy currents, the laminated core is electrically subdivided by means of at least one insulating layer between two adjacent thin sheet metal laminae.

This has the advantage, that, with only a relatively small amount of insulation on the laminated core, the possibility of axial eddy currents caused by radial and tangential flux components is reduced and reduction in eddy current losses is thus achieved, with a correspondingly lower expenditure for both materials and labour.

A further advantage resides in that the structural length of the laminated core only increases by an insignificant amount by only insulating a limited region of the thin sheet metal laminae, so that it is not necessary to change the structural length of the claw-pole rotor.

By way of example only a specific embodiment of the present invention will now be described, with reference to the accompanying drawings, in which:Fig. 1 is a longitudinal sectional view through an alternator having clawpole rotors; and Fig. 2 is an enlarged cross sectional view through the laminated core of the alternator of Fig. 1 showing the insulated central thin sheet metal laminae.

Fig. 1 is the longitudinal section of the upper half of an alternator 10, for a motor vehicle. The alternator 10 comprises in a known manner a clawpole rotor 11, whose drive shaft 12 with two ball bearings 13 is accommodated in two housing halves 14. A laminated core 15 is held by means of screws 16 between the housing halves 14, the said laminated core supports a three-phase stator winding 17 for producing electrical energy. The housing halves 14 having the laminated core 15 and the stator winding 17 form the stator 18 of the alternator 10, which has at the rear face a rectifier unit 19, a regulator 20 and a slip ring brush assembly 21, by means of which an excitation winding 22 of the claw-pole rotor 11 is supplied with direct current.

The electrical excitation produces a magnetic field between the clawpoles of the rotor 11 and the magnetic flux of this magnetic field follows the -4course, indicated in Fig. 1 by the arrows, from the north claw-poles through the laminated core 15 to the south claw-poles. By arranging the north and south claw-poles alternately about the periphery of the clawpole rotor 11, a three-phase current is produced in the stator winding 17, as soon as the claw-pole rotor 11 is driven by the internal combustion engine of the motor vehicle by way of the drive shaft 12. The magnetic field of the claw-pole rotor 11 rotating in the stator mainly has here radial and tangential flux components, which for their part cause axial and tangential eddy currents.

In order, on the one hand, to keep the eddy current losses of axial eddy currents as low as possible in the coated laminated core 15 comprising a plurality of thin sheet metal laminae 23 (see Fig. 2), and on the other hand, to limit expenditure and any increase in the dimensions of the alternator 10, when using insulating measures known per se, an insulating layer 24 is arranged between the thin sheet metal laminae 23 only in the central region of the laminated core 15. The axial eddy currents can then only develop to a limited extent in the two halves of the laminated core which are insulated from each other.

Fig. 2 shows that the insulating layer 24 is only applied to the central thin sheet metal laminae 23a, 7 t, 1 -5which are in any case manufactured separately, since they protrude from the outer periphery of the laminated core 15 and have eyelets for attachment by screws 16 for the purpose of centring the laminated core 15 on the housing half 14. The central thin sheet metal laminae 23a have a two-sided insulating layer 24.

A heat-resistant lacquer, a paper or an oxide layer is suitable as an insulating layer 24 on the surface of the laminae 23a. A clear reduction in the eddy current losses can even be achieved, if the central thin sheet metal laminae are electrically insulated from each other on approximately 10% of the thickness of the laminated core. The remaining thin sheet metal laminae 23 are not insulated. The insulating layer on the central thin sheet metal laminae 23a, and which if necessary is only to be provided on one side of the laminae, only produces a slight increase in the thickness of the laminated core, so that structural modifications are not necessary on the claw-pole rotor 11 or on the housing halves 14. In order to limit the axial eddy currents caused by the claw-pole rotor, the laminated core can if necessary, depending on its thickness, be electrically subdivided into even more segments by means of further insulating layers.

Claims

1. An alternator having a claw-pole rotor, a coated laminated core comprising thin sheet metal laminae, a stator, whose stator winding is disposed in grooves of the laminae, wherein, in order to limit the axial eddy currents, the laminated core is electrically subdivided by means of at least one insulating layer between two adjacent thin sheet metal laminae.

2. An alternator as claimed in claim 1, wherein the thin sheet metal laminae are not insulated in the outer regions of the stator laminated core and in the central region are electrically insulated from each other by means of an insulating layer.

3. An electrical machine as claimed in claim 1, wherein the central thin sheet metal laminae of the laminated core have an insulating layer on at least one side.

4. An alternator according to claim 3, wherein the central thin sheet metal laminae have attachment eyelets, protrude from the laminated core and have a two-sided insulating layer.

5. An alternator substantially as herein described, with reference to, and as illustrated in the accompanying drawings.