GB2233836A

GB2233836A - Cooling winding heads in an electric machine for a motor vehicle

Info

Publication number: GB2233836A
Application number: GB9014986A
Authority: GB
Inventors: Klaus-Georg Buerger; Kurt Weisserth; Bernhard Fakler; Martin Mueller; Gerhard Pflueger
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1989-07-08
Filing date: 1990-07-06
Publication date: 1991-01-16
Anticipated expiration: 2010-07-06
Also published as: GB2233836B; GB9014986D0

Abstract

An electric machine, for example a three-phase generator (10) for a motor vehicle, has a surface-cooled stator (11). In order to remove excess heat, generated in the winding heads (26a) of the stator winding (26), the winding heads are initially completely covered by an electrical insulating layer (27) and are then at least partially embedded in a metal die-cast alloy such as a heat-conductive material (28), by way of which the excess heat is delivered to the shrink fiber metal housing (17) and from there to a cooling medium, eg water flowing through a cooling housing into which the generator is inserted. <IMAGE>

Description

DESCRIPTION AN ELECTRIC MACHINE FOR A MOTOR VEHICLE The present invention relates to an electric machine, and in particular, but not exclusively, to a three-phase generator for a motor vehicle.

It is known from Japanese Published Utility Model Application No. JA-57-65570 to provide the stator housing of an electric motor with cooling fins for heat dissipation, which, together with annular spaces at the winding heads of the stator winding, are filled with a heat-conductive moulding resin. In such case, the winding heads are completely embedded in the moulding resin.

It is also known from Swiss Patent Specification No. 317 647 to fill up or cast around external gaps of a stator core or lamination stack of an electric machine, together with the winding heads of the stator winding, using a casting compound of casting resin or the like. The materials, used in this case to embed the winding heads provide good protection against mechanical damage to the winding heads from the outside, but they have the disadvantage of unsatisfactory heat dissipation due to unsatisfactory heat conduction values. Moreover, the resins used in this case due to the relatively large amount of shrinkage, tend to form air pockets on hardening.

It is one object of the present invention to improve heat dissipation from the winding heads to the outside environment in an inexpensive manner.

In accordance with the present invention there is provided an electric machine for a motor vehicle having a surface-cooled stator, a claw-pole rotor and a stator core or lamination stack which carries a stator winding, whose winding heads project from the grooves or slots of the stator core or stack at the two ends thereof and which is inserted into a metal housing by way of whose outer periphery excess heat is dissipated to a cooling medium, wherein the winding heads are embedded in a heat-conductive material in an electrically insulated manner and which is connected to the metal housing in a heat-conductive manner, the winding heads being initially completely covered by an electrical insulating layer and being then embedded in a metal die-cast alloy as a heat-conductive material.

This has the advantage that the metal die-cast alloy has good heat conduction, so that excess heat passes almost directly from the winding heads through the relatively thin insulating layer to the metal diecast alloy, whence it can be rapidly dissipated by way of the outer periphery of the stator housing. A further advantage is that the shrinkage of certain metal die-cast alloys is practically negligible with respect to casting compounds, so that the formation of air pockets between the insulating layer of the winding heads and the metal die-cast alloy can be reduced or avoided. Moreover, the insulating layer which completely covers the winding heads helps prevent damage to the winding heads when casting the metal diecast alloy.

Preferably, the heat conductive material is connected areally on its outer periphery to the metal housing.

The winding heads are embedded and the metal housing for the stator of the electric machine manufactured in one operation by the metal die-cast alloy, so that, in addition to good heat dissipation from the winding heads, there is also a considerable saving in costs in the manufacture of the electric machine.

It is particularly advantageous to use a zinc alloy as the metal die-cast alloy, since such a material has the characteristics required for a housing material and has a minimum amount of shrinking and requires a relatively low temperature during casting, thereby reducing the possibility of damage to the stator windings. The electrical insulating layer of the winding heads advantageously comprises a sufficiently temperature-resistant impregnating resin, in that, advantaeously, the wound stator core or lamination stack is initially immersed together with the winding heads in a liquid impregnating resin. The winding heads are not embedded in the metal die-cast alloy until the impregnating resin has hardened.A closed insulating layer which fully covers the winding heads can be advantageously obtained in that the winding heads are subjected in a heated state to plastics powder which adheres firmly to the hot surface of the winding heads and melts or is sintered-on to form a closed plastics layer about 0.5 to 1.0mum thick.

This method, which is known as whirl sintering, is particularly environmentally friendly.

Specific embodiments of the present invention are described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view through the upper half of an embodiment of a three-phase generator in accordance with the present invention; and Fig. 2 is a cross-sectional view through the upper half of a second embodiment of a three-phase generator in accordance with the present invention.

Referring to Fig. 1, an electric machine in the form of a three-phase generator 10 used to supply power in heavy motor vehicles, construction machines and the like, generally comprises a stator 11, a conducting piece rotor 12 in claw-pole form, which is fastened on a drive shaft 13, and a fixed excitation winding or induction coil 14. The rear end of the drive shaft 13 is accommodated by way of a ball bearing 15 in an end shield 16 of a pot-shaped metal housing 17 of the generator. On the drive side, the drive shaft 13 is received by way of a further ball bearing 18 by a drive flange 19 of the generator which closes off the potshaped metal housing 17 to the drive side. The excitation winding 14 is mounted in an insulated manner on a magnetic flux conducting ring 20, which is fastened by its outerface by screws 21 to the drive flange 19 and projects through the drive shaft 13.The conducting piece rotor 12 is shrunk onto the drive shaft 13 and comprises two magnetic conducting pieces 12a and 12b, which are in the form of claw poles and are magnetically insulated from one another, wherein the conducting pieces 12a and 12b are held together by two non-magnetic holding rings 22 and 23. Drive is preferably effected by an internal combustion engine by means of a belt drive by way of a pulley 24 at the drive end of the drive shaft 13.

The stator 11 of the three-phase generator 10 comprises an annular stator core or lamination stack 25, which is grooved or slotted on the inside, the grooves or slots (not shown) holding a three-phase stator winding 26, whose winding heads 26a project out of the grooves at both ends of the stator stack 25. In order to dissipate excess heat from the generator by way of the outer periphery of the metal housing 17, the three-phase generator 10 may be inserted into a closed cooling housing and connected to it by the drive flange 19, so that a cooling medium, e.g. cooling water, flowing through the cooling housing (not shown) dissipates the heat by conduction.

In order to achieve good dissipation of the excess heat from the winding heads 26a, the winding heads 26a are initially encapsulated in an electrical insulating layer 27, and then embedded in a metal diecast alloy in the form of a heat-conductive material 28. The heat-conductive material 28 is conencted areally to the inside of the metal housing 17 in order to dissipate heat. It is not absolutely necessary to completely embed the winding heads 26a in the heatconductive material 28, so that the annular inside of the winding heads 26a can remain free. Complete covering of the winding heads 26a by the insulating layer 27 is achieved, in the present case, using a plastics powder which is sintered-on onto the winding heads 26a of the pre-heated stator and in doing so creates a completely closed plastic covering approximately 1 mm thick.Since the material 28 in which the winding heads 26a are embedded has a good heat-conductive capacity, a small amount of shrinkage and a melting point which is substantially below that of copper, in order not to damage the stator winding 26 during the die-casting operation, a zinc die-cast alloy was used in the present case as the heat conductive material 28. In the present case, the outer periphery of the stator core 25 with the heat-conductive material 28 is turned to size and then the metal housing 17 is shrunk when heated onto the stator, so that the heat conductive material 28 is connected areally by its outer periphery to the metal housing 17 so as to have good heat conductivity.

In the embodiment according to Fig. 2, the three-phase generator, which is designated 30, has the same construction, with the exception of the metal housing, so that the same reference numerals have been used for the same parts as in Fig. 1. In this case, too, the winding heads 26a are initially completely covered by an electrical insulating layer 27. In contrast to the embodiment in Fig. 1, however, the winding heads 26a are embedded in a heat-conductive material made from a metal die-cast alloy, which simultaneously forms the metal housing 31. The precondition for this is that the material used should also be suitable as a housing material. The present case also uses a zinc die-cast alloy as the heatconductive material 31, since metals having a higher melting point would damage the stator winding 26 during the casting operation.

Claims

1. An electric machine for a motor vehicle having a surface-cooled stator, a claw-pole rotor and a stator core or lamination stack which carries a stator winding, whose winding heads project from the grooves or slots of the stator core or stack at the two ends thereof and which is inserted into a metal housing by way of whose outer periphery excess heat is dissipated to a cooling medium, wherein the winding heads are embedded in a heat-conductive material in an electrically insulated manner and which is connected to the metal housing in a heat-conductive manner, the winding heads being initially completely covered by an electrical insulating layer and being then embedded in a metal die-cast alloy as a heat-conductive material.

2. An electric machine as claimed in claim 1, wherein the heat-conductive material is connected areally on its outer periphery to the metal housing.

3. An electric machine as claimed in claim 1, wherein the winding heads are initially completely covered by an electrical insulating layer and are then embedded in a metal die-cast alloy as the heatconductive material, which also forms the metal housing.

4. An electric machine as claimed in either claim 1 or claim 3, wherein the heat-conductive material comprises a zinc die-cast alloy.

5. An electric machine as claimed in any of the above claims, wherein the electrical insulating layer of the winding heads comprises an impregnated resin.

6. An electric machine as claimed in any of claims 1 to 4, wherein the electrical insulating layer of the winding heads comprises a sintered-on layer of plastics material.

7. An electric machine for a motor vehicle, substantially as hereinbefore described with reference to, and as illustrated in, Fig. 1 or Fig. 2 of the accompanying drawings.