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Title:
INSULATED WINDING STACK FOR WINDING PHASE COILS USED IN ELECTROMOTIVE DEVICES
Document Type and Number:
WIPO Patent Application WO/2001/013494
Kind Code:
A1
Abstract:
An insulated winding stack provides a structure on which phase windings can be wound in their proper position. The phase windings and winding stack are incorporated as a unit into the electromotive device. A stator formed with the insulated winding stack of the present invention eliminates the 'cogging' effect caused by the metal teeth of a conventional stator. After the phase windings are formed, the windings remain on the insulated winding stack and may be impregnated with a bonding agent to maintain the integrity of the windings.

Inventors:
PHAM HA T
CAMPITIELLO LAWRENCE G
Application Number:
PCT/US2000/021809
Publication Date:
February 22, 2001
Filing Date:
August 10, 2000
Export Citation:
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Assignee:
BEI KIMCO MAGNETICS DIVISION (US)
International Classes:
H02K3/47; H02K7/116; H02K15/04; H02K15/10; H02K29/08; (IPC1-7): H02K3/47; H02K15/04; H02K15/10; H02K29/08
Foreign References:
US5525850A1996-06-11
US5323075A1994-06-21
US4709180A1987-11-24
US5714827A1998-02-03
US5030877A1991-07-09
US5850318A1998-12-15
Attorney, Agent or Firm:
Sampson, Roger S. (Limbach & Limbach L.L.P. 2001 Ferry Building San Francisco, CA, 94111, US)
Download PDF:
Claims:
I CLAIM:
1. An apparatus for constructing the stator of an electromotive device, comprising: an insulated winding stack having an inside diameter, an outside diameter and a plurality of teeth which are formed to receive phase windings; and a plurality of insulated phase windinas positioned on the plurality of teeth.
2. The apparatus of claim 1, wherein each of the plurality of insulated phase windings are formed from coils which are approximately concentric.
3. The apparatus of claim 1, wherein the insulated winding stack is formed to receive Hall Effect devices between the coils of the insulated phase windings.
4. The apparatus of claim 1, wherein the insulated winding stack is composed of one or more pieces of nonconductive plastic.
5. The apparatus of claim 1, wherein the insulated winding stack is composed of one or more pieces of a fireresistant paper product.
6. The apparatus of claim 1, wherein the plurality of teeth extend the entire length of the insulated winding stack.
7. The apparatus of claim 1, wherein the electromotive device is a direct current motor.
8. The apparatus of claim 1, wherein the direct current motor is a slotless, brushless direct current motor.
9. The apparatus of claim 1, further comprising an outer ring which has an inside diameter and an outside diameter, wherein the inside diameter of the outer ring is fitted to the outside diameter of the insulated winding stack.
10. The apparatus of claim 9, wherein the outer ring is composed of a ferromagnetic material.
11. The apparatus of claim 9, wherein the insulated winding stack is disposed between the insulated phase windings and the outer ring.
12. An insulated winding stack, comprising: an insulated core having an axis, an inner diameter and an outer diameter; and a plurality of periodicallyspaced projections extending radially from the insulated core and in the direction of the insulated core's axis.
13. The insulated winding stack of claim 12, wherein each of the plurality of periodicallyspaced projections has a predetermined crosssection in a direction transverse to the axis of the insulated winding stack.
14. The insulated winding stack of claim 13, wherein each of the plurality of periodicallyspaced projections has a"T"shaped crosssection.
15. The insulated winding stack of claim 13, wherein each of the plurality of periodicallyspaced projections extends along the entire axis of the insulated winding stack.
16. A method of forming insulated phase windings for an electromotive device which comprises a rotor and a stator, wherein the method comprises the steps of: winding the insulated phase windings around an insulated winding stack which has an inside diameter and an outside diameter; and incorporating the insulated phase windings and the insulated winding stack into the electromotive device.
17. The method of claim 16, wherein the step of incorporating comprises incorporating the insulated phase windings and the insulated winding stack into the stator of the electromotive device.
18. The method of claim 16, wherein the step of winding comprises: mounting the insulated winding stack on a winding mandrel; and winding the insulated phase windings by rotating the insulated winding stack.
19. The method of claim 16, wherein the step of winding comprises: maintaining the insulated winding stack in a fixed position; and winding the insulated phase windings on the insulated winding stack.
20. The method of claim 16, wherein the step of winding comprises forming the insulated phase windings into coils which are approximately concentric.
21. The method of claim 16, further comprising the steps of: impregnating the insulated phase windings with a bonding material; and curing the bonding material.
22. The method of claim 21, wherein the step of impregnating comprises impregnating both the insulated phase windings and the insulated winding stack.
23. The method of claim 21, further comprising the step of machining the insulating winding stack after the impregnating and curing steps.
24. The method of claim 21, wherein the step of curing comprises the step of heating the insulated winding stack and the insulated phase windings.
25. The method of claim 24, wherein the step of heating comprises the steps of: fitting a cylindrical plug into the inside diameter of the insulated winding stack before heating; and removing the cylindrical plug from the inside diameter of the insulated winding stack after heating and curing.
26. An apparatus for constructing a core structure for use in an electromotive device, comprising: an insulating section having first and second surfaces which are generally parallel to each other; and a plurality of insulated projections extending outwardly from the second surface, each of the plurality of insulated projections being a winding boundary for a coil of the electromotive device.
27. The apparatus of claim 26, wherein each of the plurality of insulated projections includes a cap portion at a point spaced away from the second surface, so that a region between the cap portion and the second surface is formed to confine a substantial portion of a coil of the electromotive device.
28. The apparatus of claim 26, wherein the insulating section has a generally cylindrical shape.
29. The apparatus of claim 28, wherein the first surface of the insulating section is on the interior of the cylindrical shape and the second surface is on the exterior of the cylindrical shape.
30. The apparatus of claim 26, wherein the insulating section has a generally planar shape.
31. The apparatus of claim 26, wherein the plurality of insulated projections extend along a longitudinal axis of the insulating section.
32. The apparatus of claim 27, wherein the cap portions extend along a longitudinal axis of the insulating section.
Description:
INSULATED WINDING STACK FOR WINDING PHASE COILS USED IN ELECTROMOTIVE DEVICES BACKGROUND OF THE INVENTION A. Field of the Invention This invention relates to the field of electromotive devices such as electric motors and generators. More specifically, this invention concerns an apparatus and method used in forming the phase windings, also known as"field coils"or "windings,"used in the stators of electromagnetic devices. The invention eliminates parasitic power losses due to"cogging"and allows the field coils to be left in place after they are wound. Although this invention has wide applicability, it is particularly useful in forming the stator phase windings of a brushless DC motor, as described below.

B. Description of the Prior Art A cross-section of a conventional stator is shown in FIG. 1. In a typical stator design, the coils are wound around"teeth"formed by ferromagnetic stator laminations. Slot insulation separates the windings from the teeth.

These teeth produce some disadvantages. As the magnet passes by each tooth, it experiences a change in magnetic reluctance. This change, referred to as "cogging"or"detent,"is not desirable for many applications.

Cogging can lead to problems in electromotive devices, including increased vibrations, noise and increased core losses. As the rotor speed increases, these problems increase proportionally.

Various methods are used to minimize the deleterious effects of cogging, e. g., small slot openings, skewing the stator stack or skewing the magnets on the rotor. However, none of these methods can entirely eliminate the effects of cogging.

As shown in FIG. 2, the slotless stator design eliminates the slot variation, since there are no ferromagnetic materials interspersed with the phase windings in the magnetic gap (i. e., the distance between the rotor and the outer ring). This design eliminates the problems caused by cogging and can produce a higher-efficiency device.

However, the conventional slotless stator design has at least two disadvantages: (1) The rotor magnet must be stronger than the magnet used with a conventional stator because the conventional slotless stator design has a larger effective magnetic gap.

This effective magnetic gap is the sum of the air gap, plus the inner insulating ring, plus the radial distance of the phase windings, plus the outside insulating ring.

In other words, the effective magnetic gap includes the entire radial distance between the outer diameter (O. D.) of the rotor magnet and the inner diameter (I. D.) of the outer ring. See FIG. 2.

(2) The phase windings take up most of the space in the effective magnetic gap, typically about 90%. To maintain the smallest effective magnetic gap, the phase windings must be as flat as possible.

Therefore, the key to building an efficient and cost effective slotless stator is the method for winding and positioning the field coils. If concentric windings are desired, the windings must be roughly consistent in radial width to maintain concentricity between the I. D. of the outer ring and the O. D. of the rotor. Good concentricity of the windings allows the air gap to be minimized.

The conventional method of winding phase coils for a slotless stator requires numerous manual hand operations, e. g., as described in U. S. Patent Nos.

5,197,180 and 5,294,855 (incorporated herein by reference) and as illustrated in FIG 3. The prior art methods for slotless stator construction are complicated and do not lend themselves to low-cost, efficient manufacturing or volume production.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a stator which does not suffer from the detrimental effects of cogging.

It is a further object of the present invention to provide a method of forming the phase windings of a stator in a simple and inexpensive manner which is suitable for volume production.

It is a further object of the present invention to provide a method for making a stator in which the phase windings can be made highly concentric.

It is a further object of the present invention to provide a stator for a brushless DC motor in which Hall Effect devices may be easily and accurately positioned, without the need for a manual timing adjustment.

To achieve the foregoing objects of the invention and other advantages, an insulated winding stack provides a structure on which phase windings can be wound in their proper position. The phase windings and winding stack are incorporated as a unit into the electromotive device. A stator formed with the insulated winding stack of the present invention eliminates the"cogging"effect caused by the steel teeth of a conventional stator. After the phase windings are formed, the windings remain on the insulated winding stack and may be impregnated with a bonding agent to maintain the integrity of the windings.

These and other features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of certain preferred embodiments of the present invention and upon consideration of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a cross-section of a conventional stator, wherein phase windings are formed around insulated steel teeth.

FIG. 2 illustrates a partial cross-section of an idealized conventional slotless stator.

FIG. 3 illustrates the first step in a conventional method of winding the phase windings of a conventional slotless stator, wherein the phase windings are formed prior to being laid on an inner insulating ring of the stator.

FIG. 4 illustrates the coil lay-up step in a conventional method of winding the phase windings of a conventional slotless stator, wherein the phase windings are laid on an inner insulating ring of the stator. In this instance, the phase windings are laid in an overlapping"wave"pattern.

FIGS. 5a and 5b illustrate the coil forming steps of forming the phase windings of a conventional slotless stator. FIG. 5a illustrates the step of bending the field coils to conform with the curved surface of the inner insulating ring. In FIG. 5b, an outside insulating ring has been fitted over the outside of the phase windings.

FIG. 6 is a cross-section of a stator which illustrates a portion of one embodiment of the present invention, in which the teeth of the insulated winding stack have been formed to receive concentric phase windings.

FIG. 7 illustrates the insulated winding stack of FIG. 6, with Hall effect devices positioned between some of the phase coils, with an outer ring (e. g., a stack-of soft steel laminations) fitted on outside the insulated winding stack and a rotor magnet inside the insulated winding stack.

FIG. 8 illustrates a perspective view of an embodiment of the insulated winding stack wherein the teeth extend the full length of the winding stack.

FIG. 9 illustrates a perspective view of a removable plug and an embodiment of the insulated winding stack.

FIG. 10 illustrates a perspective view of a removable plug and an embodiment of the insulated winding stack, wherein the plug has been inserted into the winding stack.

FIG. 11 illustrates a portion of a cross-section of a cylindrical insulated winding stack, enlarged to reveal the shape of an individual tooth.

FIG. 12 illustrates a portion of a cross-section of a planar insulated winding stack, enlarged to reveal the shape of an individual tooth.

DETAILED DESCRIPTION OF THE INVENTION FIG. 6 illustrates one embodiment of the present invention wherein insulated winding stack 1 is formed to receive three pairs of phase windings. The phase windings may be formed of any suitable conducting material, such as copper, and should be insulated.

The number of pairs of phase windings illustrated in FIG. 6 is purely illustrative; any convenient number may be used.

Insulated winding stack 1 can be formed from one or more pieces of non-conductive material, such as high-temperature injection-molded plastic, a fire- resistant paper product (e. g., Dupont"NOMEX") or other insulating material. The insulating material may be stacked and bonded like conventional motor laminations.

As illustrated in FIG. 6, insulated winding stack 1 provides a structure on which phase windings 5,7,9,11,13 and 15 can be wound. Insulated winding stack 1 can be mounted on a winding mandrel and the phase windings can be wound onto the insulated stack. For example, a conventional outside winding machine used to make brush type motor armatures may be used to wind phase windings on insulated winding stack 1. Alternatively, insulated stack 1 may be held stationary while the phase windings are wound.

Insulated winding stack 1 and phase windings 5, and 15 are later incorporated as a unit into the electromotive device. After phase windings 5,7,9,11,13 and 15 are formed, they remain on the insulated winding stack 1. The entire assembly can be impregnated with a bonding agent in order to keep phase windings and 15 in their proper positions. As illustrated in FIGS. 9 and 10, if the assembly is heated to cure the bonding agent, removable plug 21 may be inserted into the inside diameter (I. D.) of insulated winding stack 1 in order to maintain its shape. As shown in FIG. 7, it is important that the I. D. of insulated winding stack 1 be accurately maintained, because there should be a very small space between the outside diameter (O. D.) of rotor magnet 20 and the I. D. of insulated winding stack 1.

As illustrated in FIG. 7, an outer ring 17 can be fitted over the insulating winding stack. The outer ring may be made of any suitable ferromagnetic material, such as steel laminations. The insulating properties of the outer part of insulated winding stack 1 protect phase windings 5,7,9,11,13 and 15 from electrically shorting out to outer ring 17.

The insulated winding stack 1 includes projections or"teeth"2 which are formed to receive phase windings. In the preferred embodiment, teeth 2 extend the full length of the winding stack, as illustrated in FIG. 8. Insulated winding stack 1 can vary in length and diameter to accommodate the size of the rotor and the performance of the electromotive device.

FIG. 11 provides an enlarged view of a single tooth 2 and a portion of insulating core 6 of insulated winding stack 1. Here, core 6 is cylindrical in shape. FIG. 11 reveals that each tooth 2 comprises stem 4 and cap 8.

FIG. 12 provides an enlarged view of a single tooth 2A and a portion of insulating core 6A of insulated winding stack 1. Core 6A is planar in shape. FIG. 12 shows that each tooth 2A comprises stem 4A and cap 8A.

Although teeth 2 illustrated in FIGS. 6-12 are roughly"T"shaped in cross-section, any convenient shape may be used.

The O. D. of insulated winding stack 1 may change as a result of the curing process, especially if the assembly is heated to cure the bonding agent. In order to ensure that the O. D. of insulated winding stack 1 will fit inside the I. D. of outer ring 17, it is sometimes desirable to machine the O. D. of insulated winding stack 1 after the curing process, e. g., by turning insulated winding stack 1 on a lathe.

A stator formed with insulated winding stack 1 of the present invention eliminates the"cogging" effect caused by the metal teeth of a conventional stator. Moreover, the design of the present invention provides excellent concentricity between the O. D. and I. D. of the phase windings 5,7,9,11, 13 and 15 if a concentric winding pattern is used.

As shown in FIG. 7, this concentricity allows the gap between the O. D. of rotor magnet 20 and the I. D. of outer ring 17 to be minimized, thereby improving motor performance.

An additional benefit of the present invention can be realized if insulated winding stack 1 is used to form concentric windings for the stator of a brushless direct current ("D. C. ") motor. In such motors, Hall Effect devices are needed to provide commutation signals. Hall Effect devices must be accurately positioned in relation to the phase windings in order to provide accurate timing signals.

In a conventional stator for a slotless, brushless D. C. motor, Hall Effect devices must be manually positioned and the timing of each Hall Effect device must be manually checked.

When insulated winding stack 1 of the present invention is used to form the stator for a brushless D. C. motor, the positions of Hall Effect devices 19 are fixed and are placed into the slots between teeth 2 of insulated winding stack 1. See FIG. 7. Teeth 2 are formed such that these slots are midway between adjacent phase windings 5,7,9,11,13 and 15, and in the proper ratio to allow precise positioning of Hall Effect devices 19.

Consequently, this embodiment of the present invention provides more accurate positioning of Hall Effect devices 19 and allows for Hall Effect devices 19 to be positioned by machine. More accurate positioning of Hall Effect devices 19 increases timing accuracy and improves motor performance. The present invention eliminates the need for manual timing adjustments, which are required in conjunction with the prior art method of positioning the phase windings by hand.

While the foregoing is a complete description of the preferred embodiments of the present invention, various alternatives and modifications may be used.

Therefore, the preferred embodiments should not be interpreted to limit the scope of the present invention, which is defined by the following claims.