GB2312183A

GB2312183A - Method of forming a stator assembly

Info

Publication number: GB2312183A
Application number: GB9608257A
Authority: GB
Inventors: Rooij Harold Van
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1996-04-20
Filing date: 1996-04-20
Publication date: 1997-10-22
Also published as: FR2747855A1; DE19715920A1; GB9608257D0

Description

2312183 A METHOD OF FORMING A STATOR ASSEMBLY The present invention

relates to a method of forming an encapsulated stator assembly for an alternator or other form of dynamo-electric machine or electric motor.

A stator assembly is typically made by forming an annular stator core from magnetic metal laminations, with slots being formed in the inner surface of the core; positioning stator windings around the core and through the slots, the windings being of insulated electrically conductive wire; placing a metal mandrel against the inner surface of the core; impregnating the stator windings with epoxy resin; and at least partially curing the resin. A disadvantage of this method is that, due to manufacturing tolerances, a small gap is usually present between the metal mandrel and the inner surface of the core. As a consequence, during the impregnation step, epoxy resin can reach the inner surface of the stator core to form flashes of epoxy resin on the inner surface. These flashes have to be removed before the rotor assembly is positioned in the stator assembly of the assembled alternator, etc., to prevent interference with the rotor assembly. It is an object of the present invention to overcome this disadvantage. 25 A method of forming a stator assembly in accordance with the present invention comprises the steps of forming an annular stator core of magnetic metal laminates with slots in the inner surface thereof. '-. positioning stator windings of insulated electricAllY conductive wire around the stator core:ntluding thrppgh the slots; compressing a ring of silicone rubber or silicone coated rubber against the inner surface of the',, stator core; impregnating the stator windings with epoxy resin; and at least partially curing the epoxy,,rc-sixl-.

2 The compressed silicone rubber or silicone coated rubber ring forms a seal with the inner surface of the stator core to substantially prevent seepage of epoxy resin during the impregnation step. As a consequence, the additional step of epoxy resin flash removal is no longer required. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:10 Figure 1 is an end view of a metal mandrel and silicone rubber ring for use in the method of the present invention; Figure 2 is a cross-sectional view on the line II-II of Figure 1; 15 Figure 3 is a similar view to that of Figure 2 with the metal mandrel secured to a stator housing with the stator core and windings in position; Figure 4 is an enlarged cross- sectional view on the line IV-IV of Figure 3. 20 Referring to the drawings, the stator assembly 10 comprises a stator housing 12, a stator core 14 formed from magnetic metal laminations, and stator windings 16 formed from insulated electrically conductive wire (typically enamel coated copper wire). The stator core 14 is annular and has slots 18 opening through the (radially inward) inner surface 20 of the core., The stator windings 16 are positioned in the slots 18 and around the stator core 14. The stator windings 16 are impregnated with epoxy resin.

The formation of the stator core 14 with the slots 18, and the positioning of the stator windings 16 around the core and in the slots, can be achieved by any suitable method known to those skilled in the art, and will not be described herein in detail.

3 The impregnation step in the formation of the stator assembly 10, in accordance with the present invention, is achieved by the use of a metal mandrel 22 and a silicone rubber ring 24. The silicone rubber ring 5 24 is positioned adjacent the inner surface 20 of the stator core 14. The metal mandrel 22 is then secured to the stator housing 12 in any suitable manner (for example, by screws, not shown) - Figure 3. During this latter step, the silicone rubber ring 24 is compressed such that its height H in the uncompressed state is reduced (for example, by 3 mm) to a height H' in the compressed state, and its outer diameter D in the uncompressed state is increased (for example, by 0.5 mm) to an outer diameter D' in the compressed state. This compression of the silicone rubber ring 24 brings the ring into engagement with the inner surface 20 of the stator core 14, and covers the opening 26 of each slot 18 in the inner surface. As can be seen in Figure 4, the silicone rubber ring 24 is also partially extruded into the opening 26 of each slot 18 whilst in the compressed state. The sub- assembly of the stator assembly 10 with the metal mandrel 22 and silicone rubber ring 24 is then pre-heated (for example, at 80OC) and placed in a mould and epoxy resin is introduced into the mould to impregnate the stator windings 16. As the silicone rubber ring 24 is compressed against the inner surface 20 of the stator core 14, epoxy resin is prevented from reaching the inner surface. This effect is enhanced because the silicone of the rubber ring 24 has a higher coefficient of expansion than the surrounding metal components. The sub- assembly is then removed from the mould and placed in an oven to partially cure the epoxy resin (for example, at 900C for three hours). The subassembly is then removed from the oven, and the metal 4 mandrel 22 and the silicone rubber ring 24 are removed from the stator assembly 10. The compression forces within the silicone rubber ring 24 help to push the metal mandrel 22 away from the stator assembly 10. The stator 5 assembly 10 is then placed in a oven for final curing (for example, at 1300C for twelve hours).

With this method, no flashes of epoxy resin are formed on the inner surface 20 of the stator core 14, and so no additional step is required to clean the inner surface of such flashes. Additionally, the compression of the silicone rubber ring 24 to partially extrude the ring into the opening 26 of each slot 18 in the inner surface 20 of the stator core 14 causes the epoxy resin to have a concave surface 28 in each opening. With this configuration, the risk of expansion of the epoxy resin (due to temperature rises during use of an assembled alternator, etc., having the stator assembly 10 formed by the above method) out of the opening 26 of any slot 18 to bind on the rotor assembly is substantially reduced.

This latter problem can arise where the epoxy resin has a substantially flat surface across the opening of each slot because epoxy resin tends to expand more quickly during temperature rises and has a higher coefficient of expansion than the metal laminates of the stator core, and as a consequence the epoxy resin can protrude from the slots and bind the rotor assembly. Use of the compressed silicone rubber ring 24 in the method of forming the stator assembly 10 in accordance with the present invention therefore has the additional advantage of substantially overcoming this potential problem. The use of silicone rubber for the ring 24 has the advantages that it does not stick to the epoxy resin and that it will stand the temperatures associated with at least initial curing of the epoxy resin. As well as sealing with the inner surface 20 of the stator core 14 when in its compressed state, the silicone rubber ring 24 will also seal against the inner surface 30 of the stator housing 12 adjacent the stator core 14 and windings 16 to again substantially prevent leakage of epoxy resin during the impregnation step.

As an alternative to the above mentioned silicone rubber ring, a ring of other rubber material may be used (provided it is resistant to temperatures of up to 100OC) which has been coated with a release agent, such as silicone spray, may be used.

6

Claims

Claims:

1. A method of forming a stator assembly comprising the steps of forming an annular stator core of magnetic metal laminates with slots in the inner surface thereof; positioning stator windings of insulated electrically conductive wire around the stator core including through the slots; compressing a ring of silicone rubber or silicone coated rubber against the inner surface of the stator core; impregnating the stator windings with epoxy resin; and at least partially curing the epoxy resin.

2. A method as claimed in Claim 1, wherein, whilst compressed, the silicone rubber or silicone coated rubber ring is partially extruded into the opening of each slot in the inner surface of the stator core.

3. A method as claimed in Claim 1 or Claim 2, comprising the additional step of removing the silicone rubber or silicone coated rubber ring before final curing of the epoxy resin.

4. A method as claimed in any one of Claims 1 to 3, comprising the additional step of positioning the sub-assembly of stator core and stator windings in a stator housing, wherein the silicone rubber or silicone coated rubber ring is compressed by a metal mandrel which is secured to the stator housing.

5. A method as claimed in Claim 4, wherein the compressed silicone rubber or silicone coated rubber ring also engages a portion of the inner surface of the stator housing.

6. A method substantially as herein described with reference to the accompanying drawings.