GB2036456A - Winding for an Electric Motor - Google Patents

Abstract

The invention relates to a winding for a miniature electric motor. The winding consists of a former (2) which has a substantially cylindrical winding surface (9) and two axial end flanges (11, 12) adjoining the latter, and of a coil (3) which is wound upon the winding surface (9) and is laterally bounded by the two boundary faces of the end flanges (11, 12). In order to ensure a high breakdown voltage and, in some cases, to avoid the necessity of impregnation of the coil, the corners (13, 14) between the winding surface (9) and end flanges (11, 12) are rounded, individual layers of turns of the coil (3) are disposed parallel to one another, and the coil (3) is wound with a convex outer profile. The leakage path between the coil start (16) and end (17) is thereby increased in assurance. <IMAGE>

Description

SPECIFICATION Winding for a Miniature Electric Motor This invention relates to a winding for a miniature electric motor.

There are commonly employed in miniature electric motors windings having a former which has a winding surface and two boundary surfaces adjoining the latter, and a coil which is wound upon the winding surface and is laterally bounded by the two boundary surfaces. In this connection, the term "miniature electric motor" is applied to an electric motor which consumes an electric power of up to about 5 W. In special cases, the power range may reach about 10 W. Such miniature motors are often employed in appliances which are required to have high breakdown voltage, for example in tariff instruments such as meters, in clocks, etc. The required breakdown voltage is usually from 10 to 1 2 kV, measured between the beginning and the end of the electric conductor in the coil winding.

In cases where a miniature motor is of flat form, and the former is therefore also of flat form, the relatively great distance from the internally situated beginning of the coil to the externally situated coil end is frequently sufficient to ensure the required breakdown voltage. However, this distance is relatively small when the miniature motor is of large axial extent, so that additional measures must be applied to ensure the required breakdown voltage. In the prior art, one such measure resides in providing a two-chamber coil, but this involves appreciable expenditure. A further measure which is often applied consists in impregnating the coil as a whole with an insulating material, such as casting resin, after the coil has been wound. Such impregnation usually takes place at relatively high temperature in an evacuated chamber.Whilst a useful breakdown voltage can be ensured by this means, it usually entails relatively high cost, as impregnation takes place substantially manually.

The resultant difficulty may be summarised as follows. The breakdown voltage in a miniature motor winding is determined substantially by the distance between the beginning and the end of the coil and by the form of the coil. Once a particular principle has been chosen for the miniature motor, the form and the distance can no longer be varied as desired. In order to ensure a particular breakdown voltage, therefore, further steps must be taken, which involve some expenditure and lead to an increase in the cost of the miniature motor.

There is already disclosed in German Patentschrift 367 617 a coil former for an electromagnet, which is of such configuration as to prevent one turn of an upper layer from slipping down lateral boundary flanges and coming into contact with a lower turn, whereby the insulation may be punctured because of the high potential difference existing between the two turns. This configuration is such that the boundary flanges are not formed as plane surfaces perpendicular to the coil axis, but are shaped with an outwardly diverging conical or curved form, the curve commencing as far as possible in the direction of the coil axis and merging into a flange surface which is more or less perpendicular to the direction of the coil, depending upon the requirements.

In addition, there is disclosed in German Auslegeschrift 1 097 022 a cast-resin voltage transformer in which end faces of high-voitage coils employed are well-rounded and formed without edges. It may also be said that the coils are outwardly convex.

Finally, there is disclosed in German Auslegeschrift 1 764 387 an electric pancake coil in which some increase in breakdown voltage is ensured by a particular configuration of wall edges. The edges of a metal strip here employed are bevelled inwardly from an insulating layer to the centre of the strip.

Preferred embodiments of the present invention aim to provide a winding for a miniature motor, especially a winding of relatively large axial extent, such that a relatively high breakdown voltage is obtained, and impregnation in an insulating material may not be necessary in production.

According to the present invention, there is provided a winding for a miniature electric motor, wherein the winding comprises a coil wound on a coil former which comprises a substantially cylindrical winding surface bounded by two axial end flanges which are joined to the winding surface by rounded portions of the former, and the turns of the coil are arranged in parallel layers and present a convex outer profile of the coil.

To assist in understanding the invention and to show how it may be carried out, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawing, the single figure of which shows a winding for a miniature electric motor, in section.

The illustrated winding comprises a former generally denoted by 2, and a coil generally denoted by 3. The coil axis 4, is shown by a dashdotted line.

The former 2 is designed for a coil of large axial extent. In other words, the illustrated coil is relatively long in the direction of the coil axis 4. In the illustrated section, the coil 3 forms two surfaces which may be described-only very roughly-as "rectangles". The extent of these rectangles is greater in the axial direction than in a radial direction. The beginning and the end of the coil winding 3 are here. relatively close together. In contrast thereto, there exist coils of axially short construction, i.e. flat coils. In such flat coils, the extent of the "rectangles" in the axial direction is smaller than that in a radial direction.

The beginning and the end of the coil winding are then relatively far apart.

The former 2 is of rotationally symmetrical form with respect to the coil axis 4. It has a central bore 5, a central portion 6 and two flanges 7 and 8 disposed perpendicularly thereto. The outer surface of the central portion 6 serves as a cylindrical winding surface 9, and the two inner surfaces of the adjoining flanges 7 and 8 serve as boundary surfaces 11 and 12 respectively. In the sectional view shown, the former 2 is thus in the form of a double-U. Situated within this double-U is the coil 3 consisting of an electrical conductor.

As is known, a higher field strength is set up at a corner of an electric conductor than on a surface of the conductor. The same applies also to a coil of angular winding cross-section. Accordingly, in order to avoid a high field strength, the illustrated former 2 has well-rounded corners 13, 14, between the winding surface 9 and the boundary surfaces 11, 12. In this way, the distance of a wire in the lowermost layer from a wire in the uppermost layer is considerably increased in so far as the path (creeping distance) for leakage currents is concerned. Due to the rounding, there is less space for wire in the lower, first layer than in the second layer situated above it. In the winding operation, care is taken that the individual layers of the electric conductor, as seen in the illustrated section, are disposed parallel to one another.Thus, the lower, first layer, considered from the centre between the flanges 7 and 8, is not wound completely as far as the two boundary surfaces 11 and 12 extending perpendicularly to the coil axis 4. This applies also to the next, second, third and fourth layers, until the rounding of the corners 1 3, 1 4 has merged into the boundary surfaces 11, 1 2 perpendicular to the coil axis 4.

In addition, the creeping distance, which must be measured over the boundary faces 11, 12, is increased by a further measure, which resides in that the coil 3 is formed with a convex outer profile in the illustrated manner. The convex profile is denoted by 15. This is achieved by virtue of the fact that the outer layers become ever narrower up to the uppermost layer. In other words, the upper layers-as seen from the centre-are also not wound fully as far as the boundary surfaces 11 and 12.

In the figure, the beginning of the coil 3 is denoted by 1 6 and the end by 1 7. The aforesaid creeping distance is in the present case determined not by the direct geometrical connection between the beginning 1 6 and the end 17, but by a path which extends from the beginning 16 along the corner 13, along the boundary surface 11, over the left-hand outer turns of the upper layers and to the end 1 7.

Owing to this relatively long creeping path, impregnation of the coil with an electrically insulating medium can be omitted, whereby a considerable reduction of cost is obtained.

It will thus be appreciated that the illustrated coil is wound with differing numbers of turns in the individual layers of the lower and upper regions. This may be effected by a suitable cam control in the guiding of the wire in the winding operation.

As compared with a coil 3 having no rounding at the corners 13 and 14 and without a convex profile 1 5, fewer turns can be accommodated in a given winding volume in the illustrated coil. If the number of turns is nevertheless to be the same in both cases, the wire diameter must be somewhat reduced in the illustrated coil.

In embodiments of the invention, on the one hand, a relatively long distance between the beginning and the end of the coil may be obtained, and consequently high breakdown voltage, while on the other hand relatively simple production at reasonable cost may be nevertheless ensured. In many cases, the impregnation of the coil with insulating medium may be omitted, whereby the cost of production may be considerably reduced.

Claims (1)

1. Claims

   1. A winding for a miniature electric motor, wherein the winding comprises a coil wound on an annular coil former which comprises a substantially cylindrical winding surface bounded by two axial end flanges which are joined to the winding surface by rounded portions of the former, and the turns of the coil are arranged in parallel layers and present a convex outer profile of the coil.

   2. A winding according to claim 1, wherein the axial extent of the coil is greater than the radial thickness thereof.

   3. A winding for a miniature electric motor and substantially as hereinbefore described with reference to the accompanying drawing.

   4. An electric motor having a winding according to claim 1, 2 or 3.

   Amendments to claims filed on 29 February 1980.

   Superseded Claim 1 Amended Claim:

   1. A winding for a miniature electric motor, wherein the winding comprises a coil wound on a coil former which comprises a substantially cylindrical winding surface bounded by two axial end flanges which are joined to the winding surface by rounded portions of the former, and the turns of the coil are arranged in parallel layers and present a convex outer profile of the coil.