GB2139822A

GB2139822A - Stator for an electromagnetic machine

Info

Publication number: GB2139822A
Application number: GB08410975A
Authority: GB
Inventors: John David Marsh; Craig Anthony Nazzer; Edouard Hendrikus Damhuis
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1983-05-03
Filing date: 1984-04-30
Publication date: 1984-11-14
Also published as: GB8410975D0

Abstract

Electromagnetic machines of the type having circular arrays or permanent magnets (3,3a Fig. 1) arranged on a rotor (2) and a plurality of pole pieces 16 arranged on a stator (1), requires that the pole pieces be maintained in proper relationship to the permanent magnets and to one another. Means must also be provided to remove unwanted heat from the machine. The instant stator (1) of an electromagnetic machine includes a spider 10 having a plurality of bearing surfaces 15. The pole pieces 16 are positively located by the bearing surfaces 15 of the spider 10. The spider includes a plurality of walls 12, 13, 14 which, together with the pole pieces 16 define a plurality of paths 19 (21 Fig. 3) from the exterior to the interior of the spider. Cooling air is permitted to flow through the paths. <IMAGE>

Description

SPECIFICATION Stator for an electromagnetic machine This invention relates generally to electromagnetic machines, and more particularly, to motors having permanent magnet excitation and to a method for assembly of such motors.

There are, currently available, motors having circular arrays of permanent magnets arranged on a rotor. The rotor is associated with a stator having a plurality of pole pieces energized by a coil carrying a controlled electric current. Commutation of the electric current produces a rotating magnetic field in the stator, and interaction between the pole pieces and the permanent magnets results in rotation of the rotor. One example of such a motor is described in GB-A-1541211.

In designing motors of this general type, it is important to maintain the mutual inductance of the coil at the lowest possible level in order to obtain maximum utilization of the available magnetic flux, increasing the effeciency of operation and decreasing energy losses. To the extent that unavoidable energy losses do occur, heat is produced within the motor structure and it is necessary that means be provided to remove such heat from the motor. The heat problem is exacerbated by the common desire to decrease the size of the motor to permit operation in environments where space is at a premium.

Finally, it is necessary for overall efficiency of the motor that the pole pieces be maintained in proper relationship to the permanent magnets and to one another. In order to keep manufacturing costs at a minimum, it is desirable that assembly of the motor be simple and rapid while producing the desired degree of precision.

In one aspect of the present invention a stator for an electromagnetic machine is provided the stator comprising a spider having a central axis and a plurality of bearing surfaces; and annular coil wound on the spider; a plurality of U-shaped pole pieces mounted on the spider in straddling relationship to the coil, adjacent ones of the pole pieces opening in opposite radial directions from the axis and being in contact with and positively located by the plurality of bearing surfaces of the spider.

The invention also includes A method of assembling a stator of an electromagnetic machine in a stator housing, the stator having an electrical winding, a plurality of U-shaped pole pieces, and a spider, the spider having a plurality of bearing surfaces, two substantially identical halves and an intermediate complaint O-ring, the method comprising the steps of:: A) locating the spider halves in axial alignment; B) disposing the complaint O-ring between the spider halves; C) pressing the spider halves together and compressing the O-ring; D) inserting a plurality of U-shaped pole pieces adjacent alternate pairs of the bearing surfaces, the pole pieces opening radially outwardly around the spider; E) releasing the spider halves; F) laying the electrical winding around the radially outwardly opening pole pieces circumferentially of the spider; G) pressing the spider halves together again; H) inserting the remaining U-shaped pole pieces adjacent the remaining pairs of bearing surfaces, the remaining pole pieces opening radially inwardly around the spider; I) releasing the spider halves again; and, J) mounting the spider assembly in the stator housing.

The present invention is simple and low cost to manufacture and assemble, provides a highly efficient stator assembly having integral cooling capability, and is of minimal size consistent with high efficiency.

For a better understanding of the present invention, reference may be made to the accompanying drawings, in which: Figure 1 is a diagramatic view of a prior art device; Figure 2 is a fragmentary view of a part of a spider; Figure 3 is a different fragmentary view of the spider of Figure 2; Figure 4 is a sectional view of a stator housing showing air inlet and exhaust ports; and, Figure 5 (a to f) illustrates diagrammatically the stages of assembly of an embodiment of the present invention.

Figure 1 shows, diagrammatically, the basic elements of a typical motor suitable for use with an embodiment of the present invention. The machine has a stator 1 and a pair of rotors 2, each of the rotors 2 has a series of permanent magnets 3,3a, arranged equidistantly around the periphery of the rotor 2 on a magnetically permeable steel annulus 4. Alternate ones of the magnets 3,3a, have their north and south poles facing in radially opposite directions. A south pole on one rotor 2 faces a north pole on the other rotor 2 and vice-versa. The rotors 2 and stator 1 are positioned along a common central axis 5, the rotors 2 are fixed on a common shaft (not shown) for rotation relative to the stator 1.The stator 1 has a plurality of U-shaped pole pieces 6 opening alternately radially inwardly and outwardly from the axis 5, and equidistantly arranged around the periphery of the stator 1 at the same spacing as the permanent magnets 3,3a. The pole pieces 6 provide magnetic flux paths between the magnets 3,3a on the two rotors 2, on opposite sides of the stator 1. The alternating arrangement of the pole pieces 6 provides a magnetic flux path alternately inwardly and outwardly of an annular coil 7 which runs through the pole pieces 6. In response to repeatedly changing the direction of current through the coil 7, the rotors 2 rotate about the axis 5 relative to the stator 1.

Referring to Figure 2, a stator spider embodying the principles of the present invention is indicated by the reference numeral 10. It should be understood that the following detailed description relates to the best presently known embodiment of the spider 10.

However, the spider 10 can assume numerous other embodiments, as will become apparent to those skilled in the art, without departing from the appended claims.

Figure 2 is a fragmentary perspective view of one half of the stator spider 10, the other half being removed for clarity. The spider 10 has an inner hub portion 11 from which depend a series of radial walls 12,13,14. The walls 13 form a side wall of the spider 10 and have a series of generally radially extending bearing surfaces 15, which are in contact with and positively locate and support the plurality of radially inwardly and outwardly facing U-shaped pole pieces 16. Figure 2 shows only one half of the alternate outwardly facing pole pieces 16, the inwardly facing pole pieces being positioned, in use, in the stepped slots 17 shown in Figure 3.

The spider 10 is manufactured from a polymer resin and is preferably molded in two identical halves from a polyester resin having high strength and high temperature resistance, and being low in cost. Because each half of the spider is identical, only a single mold is necessary. As can be seen from Figures 2 and 3, the series of walls and webs of the spider 10 avoid problems associated with the molding of thick sections, which are both costly and impractical. The two spider halves are joined together along a plane extending perpendicularto the central axis of the spider 10 The annular coil or winding 18 which encircles the stator within the U-shaped pole pieces 16 is wound on the spider as shown in phantom in Figure 2.A pair of air cooling paths 19 feed air down between walls of the spider 10 and the laminated pole pieces 16 to a radially inward position, and through an aperture 20 onto the face of the rotors (not shown).

In use, rotation of the rotors causes a pumping action which draws air along the paths 19 towards the rotors and then generally radially outwardly between the face of the rotor and the faces of the stator, as shown at 21 in Figure 3. The paths 19 are defined in the assembled stator by the combination of the walls 13 of the spider 10, and the pole pieces 16.

Referring now to Figure 4, air is fed to the spider 10 through a series of air inlet ports 22 in a housing 23 which surrounds the spider assembly. Air leaves the gap between the rotor and spider and exits the housing 23 through exhaust ports 24.

Like the spider 10, the housing 23 is formed in two identical halves 23', the interior section of which is shown in Figure 4. The housing 23 has a series of internal abutments 25 which define a series of slots 26. The abutments 25 surround the radially outer ends of the pole pieces 16 thus preventing radially outward movement of the pole pieces 16, and provide positive location of the spider assembly.

Holes 27 are formed at the four corners of the stator housing 23 to accommodate locating bolts or rods during assembly of the machine.

The stator housing 23 provides structural rigidity for the complete stator, supports the radially inwardly opening pole pieces both radially and axially, and serves to transfer torque from the stator core to motor mounting brackets through the rods or bolts which pass through the openings 27. The housing 23 also maintains accurate alignment with other stators when the machine includes a plurality of stators, maintains an accurate gap width between the stators and the rotors, and protects the interior of the stator from external physical conditions.

Assembly of the stator is described with reference to Figure 5.

In Figure 5a, the identical molded halves of the spider 10 are located on a stub shaft 29 and positioned together on a flat assembly table 30. A compliant O-ring 31 is located in the joint between the two halves to allow the spider 10 to be pressed to a total thickness slightly less than the width of the pole pieces 16. Next (Figure 5b) the spider halves are pressed together, compressing the O-ring 31, and pole pieces 16" opening radially outwardly from the spider are inserted adjacent alternate pairs of the plurality of bearing surfaces of the spider halves. The clamping pressure on the spider halves is relieved and the hub of the spider 10 registers against locating lugs 28 on the pole pieces, as is seen in greater detail in Figure 2.The winding 18 is then laid in place (Figure 5c). The winding 18 is preferably a series of seperate spiral windings of rectangularsectioned copper stock. The two spider halves are again pressed together and pole pieces 16' opening radially inwardly from the spider are inserted adjacent the remaining plurality of bearing surfaces of the spider halves (Figure 5d). The spider halves are again released and the two halves 23' of the stator housing 23 are located (Figure 5e) around the spider assembly to complete the stator. Bolts connecting the stator housing halves 23' are then inserted and tightened to secure the assembly (Figure 5f).

The instant invention provides a statorthat is rapidly and efficiently assembled. The use of the stator spider 10 and housing 23 provides means to remove heat from the motor structure and maintains the pole pieces 16 in proper location.

Claims

1. Astatorforan electromagnetic machine, the stator comprising a spider having a central axis and a plurality of bearing surfaces; and annular coil wound on the spider; a plurality of U-shaped pole pieces mounted on the spider in straddling relationship to the coil, adjacent ones of the pole pieces opening in opposite radial directions from the axis and being in contact with and positively located by the plurality of bearing surfaces of the spider.

2. A stator according to claim 1, wherein the spider is manufactured from a polymer resin.

3. A stator according to claim 2, wherein the spider is moulded from polyester resin.

4. A stator according to any of claims 1 to 3 wherein the spider includes a pair of substantially identical halves joined together along a plane per pendicularto the axis.

5. A stator according to any of claims 1 to 4, wherein the spider includes a plurality of walls extending generally radially outwardly from the axis, the walls and pole pieces defining a plurality of cooling paths extending from the exterior to the interior of the spider.

6. A stator to any of claims 1 to 5, including a two part moulded stator housing having a plurality of cooling air inlet and outlet ports, the housing being connected to the spider and being arranged to oppose radially outward movement of the pole pieces and to provide structural rigidity for the stator.

7. A stator according to claim 6 wherein the housing includes a plurality of internal abutments and slots, the pole pieces being located within the slots and in contact with the abutments.

8. A stator according to claim 1, substantially as described with reference to the accompanying drawings.

9. A method of assembling a stator of an electromagnetic machine in a stator housing, the stator having an electrical winding, a plurality of U-shaped pole pieces, and a spider, the spider having a plurality of bearing surfaces, two substantially identical halves and an intermediate complaint O-ring, the method comprising the steps of:: A) locating the spider halves in axial alignment; B) disposing the complaint O-ring between the spider halves; C) pressing the spider halves together and compressing the O-ring; D) inserting a plurality of U-shaped pole pieces adjacent alternate pairs of the bearing surfaces, the pole pieces opening radially outwardly around the spider; E) releasing the spider halves; F) laying the electrical winding around the radially outwardly opening pole pieces circumferentially of the spider; G) pressing the spider halves together again; H) inserting the remaining U-shaped pole pieces adjacent the remaining pairs of bearing surfaces, the remaining pole pieces opening radially inwardly around the spider; I) releasing the spider halves again; and, J) mounting the spider assembly in the stator housing.

10. A method according to claim 9, substantially as described with reference to the accompanying drawings.