GB2266413A

GB2266413A - Stator construction for a two field coil dynamo electric machine.

Info

Publication number: GB2266413A
Application number: GB9208181A
Authority: GB
Inventors: Kam Shing Mok
Original assignee: Johnson Electric SA
Current assignee: Johnson Electric SA
Priority date: 1992-04-11
Filing date: 1992-04-11
Publication date: 1993-10-27
Also published as: GB9208181D0

Abstract

The laminated, ferromagnetic assembly (1) of a dynamo-electric machine has two sub-assemblies (5 and 6) which are releasably secured together by snap-fitted plugs (7) and sockets (8). Two preformed field coils (4) are respectively mounted on two core portions (3) formed on opposite sides of a pole piece (2) formed on one sub-assembly (5). The other pole piece (2) is formed on the other sub-assembly (6). Alternatively each assembly may comprise a core portion 3 and a pole portion 2 as shown in Fig 7. <IMAGE>

Description

A Dynamo-Electric Machine with Two Field Coils Field of the Invention The invention relates to dynamo-electric machines provided with two field coils.

Background Art One conventional form of dynamo-electric machine comprises a laminated, ferromagnetic assembly; two pole pieces formed in the laminated, ferromagnetic assembly; core means formed in the laminated, ferromagnetic assembly; and field coil means provided on the core means.

In constructions such as this it is convenient to form the laminated, ferromagnetic assembly as a "U"-shaped structure having two legs extending from a common crossmember.

The cross-member provides the core for a single field coil which can be conveniently wound between the two legs of the U'-shaped structure. In addition, the pole pieces may be formed in facing portions of the two legs to accommodate the rotor between these legs.

Although this form of construction limits flux leakage, in that the "U"-shaped, laminated, ferromagnetic assembly cooperates with the armature of the electro-dynamic machine to provide a low reluctance flux path, the core must be of sufficiently large cross-section to carry this flux. As a result, the length of the wire in the field coil surrounding the core is considerable. One disadvantage of excessive length of field coil wire, normally copper wire, is that this adds to the cost of the machine. Another disadvantage is that the considerable length of the wire also adds to the power loss resulting from current flow through the coil.

Disclosure of the invention The purpose of the invention is to overcome, at least to some extent, these disadvantages arising from excessive field coil wire length without completely sacrificing the ease of assembly of heretofore known constructions.

This is achieved by providing a dynamo-electric machine in which the laminated, ferromagnetic assembly comprises two stacks of ferromagnetic laminations, the two stacks are fastened together to form a closed loop, the closed loop comprises a pair of oppositely disposed first parts and a pair of oppositely disposed second parts, the two pole pieces are formed, respectively, in the pair of spaced, oppositely disposed first parts, the core means comprise two cores respectively formed in the pair of spaced, oppositely disposed second parts, and the field coil means comprise two field coils respectively provided on the two cores.

With this form of construction, the field coils may be provided on the two cores before the two stacks are fastened together, either by direct winding or by fitting preformed field coils. Both stacks of ferromagnetic laminations and, where used, both preformed field coils can be formed at the same time, in different manufacturing operations and the parts need only be brought together for final assembly.

In addition to facilitating production, as a result of the more convenient provision of the field coils, the new design is more economic in that it requires less field coil wire.

Thus, as the total magnetic flux is generated in two field coils, the core of each field coil need only have half the cross-sectional area of the core of a single field coil.

Moreover, as the total flux generated in each field coil core need only be half the flux generated in a single field coil, only half the number of turns are required in each field coil.

To illustrate the saving in coil wire it is useful to compare the length of wire required to make two turns around a first rectangular core with the length of wire required to make one turn around each of two second rectangular cores having half the cross-section of the first rectangular core.

Thus, if the first rectangular core has the outside dimensions of 2a x 2b, the length of two turns of wire around such a core would be 8a + 8b, whereas the length of a turn of wire around each of two cores having the outside dimensions of 2a x b would be 8a + 4b.

In practical applications, depending on the shape of the field coil cores, up to 30% of the copper wire used for the field coils can be saved.

The two stacks conveniently engage each other by means of two plugs and two complementary sockets having internal shapes identical with the external shapes of the two plugs. This facilitates assembly and enables the air gap between the two stacks to be is reduced to a minimum to ensure that the reluctance of the magnetic circuit is not unduly increased. In this case, each plug and its complementary socket may be snap-fitted together to fasten the two stacks together.

The two stacks may each comprise a field coil core and two pole piece halves respectively disposed on opposite sides of the field coil core. The stacks are thus joined together through the pole pieces. This has the advantage that the two magnetic circuits respectively containing the two field coil cores remain separate and there is no major flux across the join between the two halves of each pole piece. As a result, any increase in reluctance across these joints has no adverse effect on the magnetic circuits. Another advantage is that both stacks may be made from identical laminations, thus simplifying manufacture, and the field coils may be easily wound on the cores before the two stacks are fastened together.

However, with this form of construction, it is not possible to fit preformed field coils to the cores formed respectively in the two stacks.

Identical laminations may also be utilized in stacks which each comprise a pole piece and two halves of a field coil core respectively disposed on opposite sides of the pole piece. The stacks in this case are joined together through the field coil cores and so it is more convenient to use preformed field coils because this avoids the difficulty in winding field coils directly on to cores which form parts of a laminated, ferromagnetic assembly forming a closed loop. In this case, the two stacks must also be brought together by relative lateral movement parallel to the laminations forming the stacks, rather than by relative transverse movement perpendicular to the laminations forming the stacks because the core halves inside each preformed field coil have insufficient radial space to permit relative transverse movement.Thus, where the two stacks engage each other by means of two plugs and two complementary sockets, the plugs and the sockets must be shaped so as to permit this necessary relative lateral movement.

In a preferred construction, one of the stacks comprises one of the pole pieces and the two cores, respectively disposed on opposite sides of said one of the pole pieces, and the other of the stacks comprises the other of the pole pieces. This facilitates automated assembly in that the field coils can be provided on successive similarly orientated stacks comprising the two cores and then the other stacks can be successively fastened to the firstmentioned stacks.

In an alternative form of construction, each of the stacks comprises one of the pole pieces and one of the cores.

This has the advantage that both stacks can be formed from identical laminations, but stacks of this shape do not lend themselves so readily to automated assembly.

Preferably, one end of each core is fastened to a first part of the closed loop. This means that the field winding may be wound directly on the two cores or, to facilitate automated assembly, that preformed field coils can be mounted on the cores with the cores disposed within axially extending passageways formed respectively in the two preformed field coils.

The use of two preformed field coils also results in a number of subsidiary benefits. Thus, where a protective fuse is to be fitted to a field coil, it is easier to provide a planar surface on a preformed coil, for mounting the fuse, and this means that it is easier, with a preformed field coil, to use a less expensive solder fuse.

Also, by preforming the field coils, for subsequent fitting to the cores of a laminated, ferromagnetic assembly, the coils can be more rapidly wound on spools designed to be mounted on the cores of the assembly.

Moreover, with specialized winding apparatus, it is more simple to attach tapping leads to the field coil, as is commonly required in the formation of variable power universal electric motors.

Where each stack is formed from identical laminations which are shaped to form the plugs and complementary sockets, the two stacks may be brought into engagement with each other by relative transverse movement perpendic ular to the laminations of the two stacks. However, in a preferred construction, the two stacks are also shaped so that they can be fastened together by relative lateral movement parallel to the laminations of the two stacks.

In arrangements such as these, each plug may have a necked portion and an outer part which is wider than the necked portion, and each socket may have an opening having the same width as the necked portion of the plug and a space, inside the opening, which accommodates and fits the outer portion and the plug.

Thus, in a preferred embodiment of the invention, each plug has a semi-cylindrical end surface, a first planar side surface extends tangentially from one side of the semi-cylindrical end surface, a notch surface is provided adjacent the other side of the semi-cylindrical end surface, the semi-cylindrical end surface and the notch surface together provide a part-cylindrical surface extending throughout an angle of more than 1800, e.g. 1900 to 2100, each socket has a semi-cylindrical seat for the end surface of the plug, a second planar side surface extends tangentially from one side of the semi-cylindrical seat for engagement with the first planar side surface, and a lip is provided adjacent the other side of the semicylindrical seat and has an internal surface complementary with the notch surface of the plug.

Moreover, where the lip provided adjacent the other side of the semi-cylindrical seat is resiliently deformable, the plugs and the complementary sockets may be so shaped that the two stacks can be snap-fitted together by relative lateral movement parallel to the laminations of the two stacks.

The laminated, ferromagnetic assembly may also be formed in such a way that the two stacks forming this assembly are releasably fastened together. This simplifies removal of the field coils from the two stacks for repair of the dynamo-electric machine or separation of components of different materials from worn out machines for environmentally acceptable purposes such as recycling, particularly where the field coils are preformed so that they can be withdrawn bodily from the cores of the laminated, ferromagnetic assembly.

Two embodiments of the invention are hereinafter described, by way of example, with reference to the accompanying drawings.

Brief Description of the Drawings Figures 1 and 2, are end and side views of a seriesexcited universal electric motor; Figure 3 is a simplified end view of a sub-assembly forming part of the motor shown in Figures 1 and 2; Figure 4 is a more detailed exploded view of part of the sub-assembly shown in Figure 3; Figures 5 and 6 are enlarged parts of Figure 4, showing details of the construction shown in Figure 4; and Figure 7 is an exploded view similar of Figure 4, but showing a modified form of construction.

Best Modes for Carrying out the Invention As shown in Figures 1 and 2, the series-excited universal electric motor has a frame comprising a "U"-shaped member 24 and a clip 25 which grips the free ends of the legs 26 of the "U"-shaped member 24 and holds the legs 26 in engagement with a laminated, ferromagnetic assembly 1.

The clip 25 and the cross-piece 27 of the "U"-shaped member 24 are provided with bearings 28 for supporting the rotor shaft 29 of the motor so that the armature 30 is rotatable between pole pieces 2 formed in the laminated, ferromagnetic assembly 1.

Power is supplied to the motor armature 30 through supply leads 31 and 32 connected to the field coils 4 (only one of which is shown). Transfer leads 33 (only one of which is shown) extend between the coils 4 and the brushes 34 bearing on the commutator 35 to complete the circuit through the armature 30.

As shown more clearly in Figure 3, the laminated, ferromagnetic assembly l comprises a first stack 5 of laminations 7 (Figure 2) formed with two cores 3 on opposite sides of a first pole piece 2. A second stack 6 of laminations 7 is formed with a second pole piece 2 and is releasably connected to the first stack 5 by means of plugs 10 formed on the ends of the cores 3, which are snap-fitted in complementary sockets 11 formed in the second stack 6. The two stacks 5 and 6 are thus fastened together to form a closed loop with the two pole pieces 2 formed, respectively, in a pair of spaced, oppositely disposed first parts 8 and the two cores 3 formed, respectively, in a pair of spaced, oppositely disposed second parts 9.Preformed field coils 4 comprising hollow insulating spools 36 wound with copper wire 37 are fitted over both cores 3 (even though, for the sake of clarity, only one preformed field coil 4 is shown).

As shown in Figure 4, each stack 5 and 6 of the laminated, ferromagnetic assembly 1 is formed with a recess 38 for receiving the legs 26 of the "U"-shaped member 24. Figure 4 also shows how the plugs 10 on the cores 3 are resiliently engageable with the complementary sockets 8 formed in the second stack 6 of the laminated, ferromagnetic assembly 1. This is more clearly shown in the enlarged drawings of one of the plugs 10 and one of sockets 11 shown in Figures 5 and 6.

Thus, each plug 10 has a semi-cylindrical end surface 16 and a first planar surface 17 extending tangentially from one side of the semi-cylindrical end surface 16. A notch surface 18 is provided adjacent the other side of the semi-cylindrical end surface 16 so that the semicylindrical end surface 16 and the notch surface 18 together provide a part-cylindrical surface 19 which extends through an angle of approximately 2000 and surrounds an outer part 13 of the plug 10 which is wider than a necked part 12 which is bounded, on opposite sides, by the first planar surface 17 and the notch surface 18.

Similarly, each socket 11 has a semi-cylindrical seat 20 for receiving the end surface 16 of the plug 10, a second planar surface 21 extending tangentially from one side of the semi-cylindrical seat 20 to engage the first planar surface 17. The socket 11 also has a resiliently deformable lip 22 provided adjacent the other side of the semi-cylindrical seat 20 and having an internal surface 23 which is complementary to the notch surface 18. Thus, when the plug 10 is pushed into the socket 11, the lip 22 deforms, allowing the end 16 of the plug 10 to engage the seat 20 of the socket 11, and then resumes its normal position so as to resist removal of the plug 10 from the socket 11. The two stacks 5 and 6 may be prised apart, involving deformation of the lips 22, or the stacks 5 and 6 may be separated by relative transverse movement perpendicular to the laminations 7.

In a modified form of the invention, assembly 1 has two identical stacks 5 and 6, as shown in Figure 7. Thus, each of the stacks 5 and 6 has a pole piece 2, a recess 38, a core 3 provided with a plug 10 on one side, and a socket 11 on the other side. The plugs 10 on the first and second stacks 5 and 6 make snap-fit connections with the sockets 11 in the second and first stacks 6 and 5 similar to the snap-fit connections shown in Figure 4.

Claims

1. A dynamo-electric machine in which a laminated, ferromagnetic assembly (1) comprises two stacks (5 and 6) of ferromagnetic laminations (7), the two stacks (5 and 6) are fastened together to form a closed loop, two pole pieces (2) are formed respectively in a pair of spaced, oppositely disposed first parts (8) of the closed loop; two cores (3) are formed respectively in a pair of spaced, oppositely disposed second parts (9) of the closed loop; and two field coils (4) are respectively provided on the two cores (3).

2. A machine, according to Claim 1, in which the two stacks (5 and 6) engage each other by means of two plugs (10) and two complementary sockets (11).

3. A machine, according to Claim 1 or Claim 2, in which one of the stacks (5 and 6) comprises one of the pole pieces (2) and the two cores (3), respectively disposed on opposite sides of said one of the pole pieces (2), and the other of the stacks (5 and 6) comprises the other of the pole pieces (2).

4. A machine, according to Claim 1 or Claim 2, in which each of the stacks (5 and 6) comprises one of the pole pieces (2) and one of the cores (3).

5. A machine, according to Claim 3 or Claim 4, in which one end of each core (3) is fastened to a first part (8) of the closed loop.

6. A machine, according to Claim 5, in which the two field coils (4) are preformed, a hollow, axially extending passageway (16) is formed in each field coil (4), and the two cores (3) are respectively disposed within the two passageways (16).

7. A machine, according to Claim 5 or Claim 6, in which said one end of each core (3) is formed with a plug (10) and the first part of the closed loop to which said one end is fastened is formed with a complementary socket (11) to receive said plug (10).

8. A machine, according to Claim 2 or Claim 7, in which each plug (10) and its complementary socket (11) are snapfitted together.

9. A machine, according to Claim 2 or Claim 7, in which the plugs (10) and the complementary sockets (11) are shaped so that the two stacks (5 and 6) can engage each other by relative lateral movement parallel to the laminations (7) of the two stacks (5 and 6).

10. A machine, according to Claim 2 or Claim 7, in which each plug (10) has a necked portion (12) and an outer part (13) which is wider than the necked portion (12), and each socket (11) has an opening (14) having the same width as the necked portion (12) of the plug (10) and a space (15), inside the opening (14), which accommodates and fits the outer portion (13) and the plug (10).

11. A machine, according to Claim 2 or Claim 7, in which each plug (10) has a semi-cylindrical end surface (16), a first planar side surface (17) extends tangentially from one side of the semi-cylindrical end surface (16), a notch surface (18) is provided adjacent the other side of the semi-cylindrical end surface (16), the semi-cylindrical end surface (16) and the notch surface (18) together provide a part-cylindrical surface (19) extending throughout an angle of more than 1800, each socket (11) has a semi-cylindrical seat (20) for the end surface (16) of the plug (leo), a second planar side surface (21) extends tangentially from one side of the semi-cylindrical seat (20) for engagement with the first planar side surface (17), and a lip (22) is provided adjacent the other side of the semi-cylindrical seat (20) and has an internal surface (23) complementary with the notch surface (18) of the plug (10).

12. A machine, according to Claim 10 or Claim 11, in which the plugs (10) and the complementary sockets (11) are shaped so that they can be fastened together by relative lateral movement parallel to the laminations (7) of the two stacks (5 and 6) and are snap-fitted together.

13. A machine, according to any preceding claim, in which the two stacks (5 and 6) are releasably fastened together.