GB2234400A

GB2234400A - Heat sink for winding heads of an electric machine for a motor vehicle

Info

Publication number: GB2234400A
Application number: GB9014987A
Authority: GB
Inventors: Leypold Falko
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1989-07-08
Filing date: 1990-07-06
Publication date: 1991-01-30
Anticipated expiration: 2010-07-06
Also published as: GB2234400B; FR2649556B1; DE8915212U1; JP2859387B2; JPH0345141A; GB9014987D0; FR2649556A1

Abstract

An electric machine, for example a three-phase generator (10) for a motor vehicle, has a surface-cooled stator (11). To dissipate excess heat generated in the winding heads (26a, 26b) of the stator winding (26), at least one of the winding heads (26a) is surrounded by a metal ring (27) which is press fitted between the metal housing (17) and the winding head (26a) and is areally connected over the entire depth of the winding head (26a) to the metal housing (17). A gap remaining between the winding head (26a) and the metal ring (27) is filled with a heat-conducting plastics material (29). Dual stator embodiments Fig 2, 3 are disclosed. <IMAGE>

Description

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

It is known from 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.

Finally, it is known from German Offenlegungsschrift No. 27 11 053, in order to dissipate the heat generated in the rotor of the machine, to dispose heat conducting rings in front of the winding heads of the stator winding, whose comb-like projections are inserted into the stator grooves or slots, and which abut on their outer periphery against the stator housing for heat dissipation. As a result of this measure, the stator winding is largely protected from heat radiation from the rotor, wherein the winding heads are embedded through bores in the heat conducting rings in an insulating material which serves to both thermally and electrically insulate the winding heads. The electrical heat generated in the winding heads must consequently be dissipated to the housing by way of the stator core.

It is one object of the present invention to improve heat dissipation from the winding heads to the outside environment in an effective and 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 lamination stack on the two end faces thereof and which is inserted into a metal housing by way of whose outer periphery excess heat is dissipated to a cooling medium, the winding heads being enclosed in an electrically insulated manner by a heat-conducting metal ring which is connected to the metal housing in a heat-conducting manner, wherein between the metal housing and at least one of the winding heads, a metal ring, which projects closely over the end face of the respective winding head, is pressed against the stator core or stack and is areally connected along substantially the entire depth of the respective winding head to the metal housing and a gap remaining between the winding head and the metal ring in each case is filled with a plastics material.

This has the advantage that the heat conducting rings can substantially directly absorb excess heat produced in the winding heads through the relatively thin insulating layer and can then dissipate it by way of the outer periphery of the machine housing. A further advantage is to be found in that the shrinkage of the casting compounds used is negligible, so that the formation of air pockets or air gaps between the insulating layer of the winding head and the metal ring can be avoided.

It is particularly advantageous to provide a metal ring enclosing a winding head on one side only of the stator core or lamination stack of the electric machine and to provide the metal housing of the stator on the other side of the stator core with an inner shoulder, which acts as a stop for the stator core and extends closely over the winding head, as well as to provide it with an annular, radially inwardly directed projection, which covers the end face of this winding head. In an electric machine having two stator windings disposed axially one behind the other, as normally used in double-conducting-piece generators, it is particularly advantageous to provide the housing of the machine between the two stator cores or lamination stacks with an inwardly directed collar, which has a T-shaped cross-section and which covers the adjacent inner winding heads for heat dissipation.The two outer winding heads are in such case to be covered by two angular metal rings which are press-fit into the metal housing. In the case of a pot-shaped housing of the stator, however, it is advantageous, in place of the T-shaped housing collar, to use a T-shaped metal ring for the two adjacent inner winding heads, which at the same time acts as a stop for the adjacent stator cores.

Specific embodiments of the present invention are described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig.l is a cross-sectional view through one embodiment of an electric machine in accordance with the present invention, illustrating the upper half of a three-phase generator having a heat conducting ring; Fig.2 is a cross-sectional view through a second embodiment of the electric machine illustrating the lower half of a double-conducting-piece three-phase generator having two heat conducting rings and a T-shaped housing collar between the stator cores or lamination stacks; and Fig.3 is a cross-sectional view through a third embodiment of the electric machine illustrating a double-conducting-piece three-phase generator having a T-shaped middle heat conducting ring and two outer heat conducting rings.

Referring to Fig.l, an electric motor in the form of a three-phase generator 10 is used to supply power in heavy motor vehicles, construction machines and the like. It 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 pot-shaped metal housing 17 to the drive side. The excitation winding 14 is mouned in an insulated manner on a magnetic flux conducting ring 20, which is fastened by its outer face 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 either end face of the stator core 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 excess heat.

In order to achieve good dissipation of the excess heat from the winding heads 26a and 26b, a metal ring 27 is pressed into the metal housing 17 against the stator core or lamination stack 25 between the metal housing 17 and the left-hand winding head 26a. The metal ring 27 has an angular cross section and extends closely over the end face of the front winding head 26a. The metal ring 27 is areally connected by its outer periphery, along the entire depth of the winding head 26a, to the metal housing 17 for good heat dissipation. On the left-hand side of the stator core 25 remote from the metal ring 27, the metal housing 17 of the stator 11 is provided with an inner shoulder 28 for dissipating the heat from the left-hand winding head 26b, which shoulder acts as a stop for the stator core 25 and extends closely over the winding head 26b.Contiguous therewith, the housing 17 is provided with an annular, radially inwardly directed projection 17a, which covers the end face of this winding head 26b. Gaps remaining between the winding head 26a and the metal ring 27 and the winding head 26b and the projection 17a are filled with a preferably heatconducting plastics material 29.

In the embodiment illustrated in Fig.2, the lower half of a three-phase generator 30 has a doubleconducting-piece rotor 31. Two conducting-piece rotors 33,34 are fastened in claw-pole form on a drive shaft 32 in a mirror-inverted manner, wherein the claw-poles each cover one of two excitation windings or induction coils 35,36 respectively. Each of the excitation windings 35,36 is mounted in an insulated manner on a magnetic flux conducting ring 37,38, which is screwed by its end face to a housing flange 39,40 of the three-phase generator 30. The stator 41 of the three-phase generator 30 is provided with two stator cores or lamination stacks 42,43 which are disposed axially one behind the other, are surrounded by a metal housing 44 which is provided with cooling medium channels, and carry stator windings 45,46.

The two outer winding heads 45a and 46a of the stator windings 45,46 are each covered by two angular metal rings 27 as previously discussed with respect to Fig.l for heat dissipation. The adjacent inner winding heads 45b,46b are in this case covered by an inwardly directed collar 47 of the metal housing 44 which has a T-shaped cross section. In this case too, the sides of the T-shaped housing collar 47 each form a stop for the stator cores 42 and 43.

While the two flux-conducting-piece systems of the three-phase generator 30 in Fig.2 are put together from both end faces, Fig.3 shows a further embodiment in which a double-conducting-piece three-phase generator 50 has a pot-shaped metal housing 51, which is closed off by a flange 52 on the drive side only.

In place of the collar 47 formed on the housing in Fig.2, an H-shaped metal ring 53 is pressed areally into the metal housing 51 between the stator cores 42,43, which are disposed axially one behind the other, for heat dissipation, and encloses the inside winding heads 45b, 46b. The outer winding heads 45a and 46a are surrounded in this case by U-shaped metal rings 54,55, which also cover the inner periphery of the winding heads up to an air gap in front of the stator core or lamination stack 45 and/or 46. A preferably conductive plastics material is in turn inserted through the air gaps to fill up the spaces between the winding heads and the metal rings 53, 54 and 55. In a preferred embodiment, these spaces have silicon caoutchouc sprayed therein. Particularly good heat dissipation to the metal housing is achieved when the metal rings 53, 54, 55, which are pressed areally into the metal housing 52, are made of aluminium.

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 lamination stack on the two end faces thereof and which is inserted into a metal housing by way of whose outer periphery excess heat is dissipated to a cooling medium, the winding heads being enclosed in an electrically insulated manner by a heat-conducting metal ring which is connected to the metal housing in a heat-conducting manner, wherein between the metal housing and at least one of the winding heads, a metal ring, which projects closely over the end face of the respective winding head, is pressed against the stator core or stack and is areally connected along substantially the entire depth of the respective winding head to the metal housing and a gap remaining between the winding head and the metal ring in each case is filled with a plastics material.

2. An electric machine as claimed in claim 1, wherein on one end face of the stator core or stack the metal housing of the stator has an inner shoulder, acting as a stop for the stator core or stack and extending closely over a winding head, and being formed with an annular, radially inwardly directed projection, which covers the end face of this winding head.

3. An electric machine as claimed in either of claims 1 or 2, wherein the machine is a doubleconducting-piece machine, in which between two stator cores or stacks, which are axially adjacently disposed at a distance, an inwardly directed collar of the metal housing, having a T-shaped cross section, covers the adjacent inner winding heads for heat dissipation, and the two outer winding heads are covered by two angular metal rings.

4. An electric machine as claimed in claim 3, wherein the sides of the T-shaped collar form a stop for the two stator cores or stacks.

5. An electric machine as claimed in claim 1 or 2, wherein the machine is a double-conducting-piece machine, in which betwen two stator stacks disposed axially adjacent to one another at a distance, an H-shaped metal ring, which encloses the adjacent inner winding heads, is pressed areally into the metal housing for heat dissipation.

6. An electric machine as claimed in any of the above claims, wherein a gap remaining between the winding head and metal ring and/or metal housing respectively has a heat-conducting, electrically insulating plastics material such as silicon caoutchouc sprayed therein.

7. An electric machine as claimed in any of the preceding claims, wherein the metal rings, which are pressed areally into the metal housing, comprise aluminium.

8. An electric-machine for a motor vehicle, substantially as hereinbefore described with reference to and as illustrated in, Fig.l, Fig.2 or Fig.3 of the accompanying drawings.