Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1997-07-18
1999-11-16
LaBalle, Clayton
Electrical generator or motor structure
Dynamoelectric
Rotary
310179, H02K 110, H02K 114, H02K 100
Patent
active
059863765
DESCRIPTION:
BRIEF SUMMARY
This invention relates to brushless DC motors.
FIGS. 1 and 2 of the accompanying drawings show a known form of brushless DC motor. The brushless DC motor of FIGS. 1 and 2 comprises a cylindrical rotor 10 mounted for rotation about an axis A--A within a cylindrical stator 12 mounted so as to be coaxial with the rotor. The rotor 10 and stator 12 have confronting surfaces, namely the outer surface of the rotor and the inner surface of the stator, spaced apart by an air gap. Permanent magnets M in the form of bars are mounted on one of the above-mentioned confronting surfaces, namely the outer surface of the rotor 10. The magnets M (of which two only are shown in FIG. 1) are equally angularly spaced around the axis A--A of rotation of the rotor 10 such that each magnet occupies part of (and preferably substantially the whole of) a respective pole arc PA. Each pole arc PA is a respective arc of a first circle C1 (FIG. 2) of radius r1 which is centred upon the axis A--A and passes through the magnets M. Each pole arc PA subtends a common angle (pole angle) a to the axis A--A, whereby the pole arcs are equal to each other. (By virtue of the fact that FIG. 2 is a linear development, each pole arc PA appears in FIG. 2 as a rectilinear dimension rather than an arcuate dimension. Likewise, the surfaces of the magnets M facing the stator 12 appear flat rather than arcuate (convex).)
As can be seen by the reference signs N (North pole) and S (South pole) in FIG. 2, the magnets M are magnetised radially of the axis A--A with adjacent magnets being magnetised in opposite directions.
The stator 12 is of a ferromagnetic material and is formed in a manner known per se by a stack of like laminations (not shown) spaced apart along the axis A--A and secured to and electrically insulated from one another. By appropriate stamping of the laminations, teeth 14 are provided at the other of the above-mentioned confronting surfaces. namely the inner surface of the stator 12. The teeth 14 are equally angularly spaced from one another around the axis A--A of rotation of the rotor 10 such that each tooth occupies part of (and preferably substantially the whole of, subject to the constraint of leaving gaps to permit formation of the windings mentioned below) a respective tooth arc TA. Each tooth arc TA is a respective arc of a second circle C2 (FIG. 2) of radius r2 which is centred upon the axis A--A and passes through the teeth 14. Each tooth arc TA subtends a common angle (tooth angle) .beta. to the axis A--A, whereby the tooth arcs are equal to each other. (By virtue of the fact that FIG. 2 is a linear development, each tooth arc TA appears in FIG. 2 as a rectilinear dimension rather than an arcuate dimension. Likewise, the surfaces of the teeth 14 facing the rotor 10 appear flat rather than arcuate (concave).)
The teeth 14 are substantially T-shaped with the uprights of the Ts extending radially of the axis A--A of rotation of the rotor 10 and with the cross bars of the Ts facing the permanent magnets M across the air gap.
In general terms, brushless DC motors can employ either pitched winding or tooth winding. It will be assumed in the following that tooth winding (which has the potential advantage of better use of copper) is employed.
As shown in FIG. 2, a respective winding 16 is wound around the upright of the T of each of the teeth 14. Although not shown in FIG. 1, the teeth 14 extend axially along the whole axial length of the stator 12, whereby the windings 16 do likewise.
The windings 16 are electrically connected together in sets, where each set represents a phase of the motor. Each winding set may be formed by connecting together the windings 16 on a group of adjacent teeth 14. Alternatively, each winding set may be formed by connecting together the windings 16 on teeth 14 which are distributed around the stator 12 and spaced by teeth having windings belonging to another set or sets. The manner of connection of the windings 16 will be dependent on the number of magnets M, the number of phases and the number of teeth 14 per
REFERENCES:
patent: 5418416 (1995-05-01), Muller
patent: 5442250 (1995-08-01), Stridsberg
Automotive Motion Technology Limited
LaBalle Clayton
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