GB2115987A - Dynamoelectric machines - Google Patents

Abstract

An a.c. electrical machine having no enclosing shell, has a stator comprising laminations 15 secured under axial pressure between two pressure members 17 and 18. The rotor comprises laminations secured to a shaft under axial pressure between two pressure members (40 Figure 6), one member being located against an abutment (41) on the shaft and the other member for being axially secured by a shrink fit collar (42). <IMAGE>

Description

SPECIFICATION Dynamoelectric machines The present invention relates to electrical machines and is specially concerned with a.c. electrical machines.

By an a.c. machine is meant not only a.c. machines of traditional design but also modern machines in which the a.c. supplied to the machine is synthesised from a d.c. supply by electronic or other control means.

A.c. machines have previously been constructed with a laminated stator mounted within a cast or fabricated shell. It is an object of the present invention to provide a stator construction that is electrically more efficient and which does not require a shell.

The present invention is an a.c. electrical machine comprising a stator and a rotor, the stator comprising laminations secured between two pressure members and having no enclosing shell.

The present invention is also a method of making a stator of an a.c. electrical machine comprising providing a stack of laminations, and two pressure members, machining faces of the pressure members to compensate for any misalignment of the end faces of the stack and securing together the stack and the pressure members so that the stack is compressed between the pressure members.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 7 shows the overall assembly of an a.c.

machine according to the present invention; Figure2 shows a typical stator/rotor lamination used in machines according to the present invention; Figures 3, 4 and 5 show details of a stator frame assembly in side and end elevations respectively; Figure 6shows a rotor shaft assembly; Figure 7shows a rotor end plate; and Figure 8 shows a modified rotor assembly in side elevation.

Referring now to Figure 1, an electrical a.c.

machine is shown which has a rotor 10 mounted on a shaft 11 which is carried in bearings 13 in end brackets 25 and 26 carried by a fully laminated stator 12 which is self supporting, i.e. no frame is necessary.

As seen best in Figure 3, the stator lamination pack 15 is sandwiched between two pressure members 17 and 18 such as castings or plates, the pack being secured, in this embodiment, by studs 19 passing from one plate 17 through the pack 15 to the other plate 18. The end faces 20 and 21 of the plates 17 and 18 respectively are machined to compensate for the shape of the stator pack 15 (which tends to have end faces which are not perpendicular to the axis of the pack) and end brackets 25 and 26 are mounted on the pressure plates (Figure 1). The end brackets 25 and 26 have had their spigot locations and bearing housings machined in a single operation to ensure accurate centering and thus minimal variation in the air gap between the rotor 10 mounted in the bearings 13 in the end brackets 25 and 26 and the interior surface of the stator.

The stator laminations (as seen in Figure 2) themselves are substantially square on their outer periphery and are provided with cooling apertures 30 which in the assembled stack provide cooling ducts and which also accommodate the studs 19. In an alternative embodiment separate holes are provided for the studs 19.

It should be understood that Figure 2 shows a combined stator/rotor lamination with stator/rotor slots 31, rotor cooling holes 32 and a central aperture 33 for the shaft 11. Only one slot 31 is shown and the rotor/stator cut is through the slots 31.

This design of stator offers advantages over conventional designs, of increased output, reduced losses, improved power factor, efficient cooling and no frame.

The rotor laminations incorporate cooling holes 32 and are sandwiched, together with rotor pressure plates 40, on the shaft 11 as shown in Figure 6 between an abutment, for example a circlip 41 and, in this embodiment, a shrink fit collar 42. By applying proper pressure during assembly, a pre-stress tube effect is obtained thus effectively increasing the second moment of area of the shaft and hence the stiffness of the assembly and aliowing the use of a smaller shaft 11 of substantially constant diameter.

The rotor pressure plates 40 (Figure 7) are provided with holes 44 in register with the cooling ducts 45 in the lamination stack which direct cooling air onto the end rings 46 as shown in Figure 6.

The rotor may also be provided as shown in the modified rotor of Figure 8 with circumferential conducting rings 50. These rings act to suppress noise and support rotor bars in open-slot designs.

The intermediate rings 50 are secured in position by M.l.G. (metal inert gas) orT.l.G. (tungsten inert gas) weiding methods.

Utilising these techniques and by correct selection of values of leakage inductance and resistance of the rotor and stator circuits, an induction motor can be produced which has a flat or rising torque speed characteristic ideally suited for solid-state inverter drives without having substantially to derate the machine.

1. An a.c. electrical machine comprising a stator and a rotor, the stator comprising laminations secured under axial pressure between two pressure members and having no enclosing shell.

2. A machine as claimed in claim 1, in which the stator laminations are substantially square.

3. A machine as claimed in claim 1 or claim 2, the rotor comprising laminations secured on a shaft between two pressure members, one pressure member being located by an abutment on the shaft and the other member being axially secured by a shrink fit collar to give a rigid rotor assembly.

4. A machine as claimed in claim 3, in which the rotor pressure member design is such as to direct cooling air flowing through the rotor onto the end rings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Dynamoelectric machines The present invention relates to electrical machines and is specially concerned with a.c. electrical machines. By an a.c. machine is meant not only a.c. machines of traditional design but also modern machines in which the a.c. supplied to the machine is synthesised from a d.c. supply by electronic or other control means. A.c. machines have previously been constructed with a laminated stator mounted within a cast or fabricated shell. It is an object of the present invention to provide a stator construction that is electrically more efficient and which does not require a shell. The present invention is an a.c. electrical machine comprising a stator and a rotor, the stator comprising laminations secured between two pressure members and having no enclosing shell. The present invention is also a method of making a stator of an a.c. electrical machine comprising providing a stack of laminations, and two pressure members, machining faces of the pressure members to compensate for any misalignment of the end faces of the stack and securing together the stack and the pressure members so that the stack is compressed between the pressure members. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 7 shows the overall assembly of an a.c. machine according to the present invention; Figure2 shows a typical stator/rotor lamination used in machines according to the present invention; Figures 3, 4 and 5 show details of a stator frame assembly in side and end elevations respectively; Figure 6shows a rotor shaft assembly; Figure 7shows a rotor end plate; and Figure 8 shows a modified rotor assembly in side elevation. Referring now to Figure 1, an electrical a.c. machine is shown which has a rotor 10 mounted on a shaft 11 which is carried in bearings 13 in end brackets 25 and 26 carried by a fully laminated stator 12 which is self supporting, i.e. no frame is necessary. As seen best in Figure 3, the stator lamination pack 15 is sandwiched between two pressure members 17 and 18 such as castings or plates, the pack being secured, in this embodiment, by studs 19 passing from one plate 17 through the pack 15 to the other plate 18. The end faces 20 and 21 of the plates 17 and 18 respectively are machined to compensate for the shape of the stator pack 15 (which tends to have end faces which are not perpendicular to the axis of the pack) and end brackets 25 and 26 are mounted on the pressure plates (Figure 1). The end brackets 25 and 26 have had their spigot locations and bearing housings machined in a single operation to ensure accurate centering and thus minimal variation in the air gap between the rotor 10 mounted in the bearings 13 in the end brackets 25 and 26 and the interior surface of the stator. The stator laminations (as seen in Figure 2) themselves are substantially square on their outer periphery and are provided with cooling apertures 30 which in the assembled stack provide cooling ducts and which also accommodate the studs 19. In an alternative embodiment separate holes are provided for the studs 19. It should be understood that Figure 2 shows a combined stator/rotor lamination with stator/rotor slots 31, rotor cooling holes 32 and a central aperture 33 for the shaft 11. Only one slot 31 is shown and the rotor/stator cut is through the slots 31. This design of stator offers advantages over conventional designs, of increased output, reduced losses, improved power factor, efficient cooling and no frame. The rotor laminations incorporate cooling holes 32 and are sandwiched, together with rotor pressure plates 40, on the shaft 11 as shown in Figure 6 between an abutment, for example a circlip 41 and, in this embodiment, a shrink fit collar 42. By applying proper pressure during assembly, a pre-stress tube effect is obtained thus effectively increasing the second moment of area of the shaft and hence the stiffness of the assembly and aliowing the use of a smaller shaft 11 of substantially constant diameter. The rotor pressure plates 40 (Figure 7) are provided with holes 44 in register with the cooling ducts 45 in the lamination stack which direct cooling air onto the end rings 46 as shown in Figure 6. The rotor may also be provided as shown in the modified rotor of Figure 8 with circumferential conducting rings 50. These rings act to suppress noise and support rotor bars in open-slot designs. The intermediate rings 50 are secured in position by M.l.G. (metal inert gas) orT.l.G. (tungsten inert gas) weiding methods. Utilising these techniques and by correct selection of values of leakage inductance and resistance of the rotor and stator circuits, an induction motor can be produced which has a flat or rising torque speed characteristic ideally suited for solid-state inverter drives without having substantially to derate the machine. CLAIMS

1. An a.c. electrical machine comprising a stator and a rotor, the stator comprising laminations secured under axial pressure between two pressure members and having no enclosing shell.

2. A machine as claimed in claim 1, in which the stator laminations are substantially square.

3. A machine as claimed in claim 1 or claim 2, the rotor comprising laminations secured on a shaft between two pressure members, one pressure member being located by an abutment on the shaft and the other member being axially secured by a shrink fit collar to give a rigid rotor assembly.

4. A machine as claimed in claim 3, in which the rotor pressure member design is such as to direct cooling air flowing through the rotor onto the end rings.

5. A method of making a stator of an a.c.

electrical machine comprising providing a stack of laminations, and two pressure members, machining faces of the pressure members to compensate for any misalignment of the end faces of the stack and securing together the stack and the pressure members so that the stack is compressed between the pressure members.

6. A method as claimed in claim 5, in which end brackets, in which rotor bearings are mounted and which are located on the pressure members on spigots, have their spigot locations and bearing housings machined simultaneously.

7. An a.c. electrical machine substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

8. A method of making a stator of an a.c.

electrical machine substantially as hereinbefore described with reference to the accompanying drawings.