Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1997-07-24
1999-01-19
Dougherty, Thomas M.
Electrical generator or motor structure
Dynamoelectric
Rotary
310 45, 310 43, 310254, H02K 117, H02K 127
Patent
active
058616950
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an inductor for an electric rotary machine comprising sintered permanent magnets embedded in a ferromagnetic binder.
Electric rotary machines are chiefly electric motors or electric generators, for example for automobile auxiliary equipment; they comprise an inductor which is generally the stator but sometimes the rotor.
DESCRIPTION OF RELATED ART
Usually an inductor comprises a yoke, a cylindrical tubular piece whose cross-section has at least one axis of symmetry and a shape which is generally circular, polygonal or square with rounded corners.
One or more permanent magnets made of hard magnetic material are attached to the inner wall of the yoke, which is made of soft magnetic material. They can be of annular shape, a single magnetized piece covering the inner periphery of the cross-section, or in the form of several magnetized parts symmetrically distributed on this periphery; these pieces can have a cross-section that is for example rectangular, or preferably can be a section of a circular ring, or can have at least one surface of circular cross-section adapted to the armature.
These permanent magnets can be sintered pieces, or bound composite magnets, the magnetized material for example being embedded in a solid resin. They are such that they leave a space at the center of the yoke in which the armature of the rotary machine is located.
Pole pieces be added to the permanent magnets on the armature side in order to modify the magnetic flux and improve the performance of the rotary machine.
The active material of the permanent magnets is of a known type, for example ferrite, an alloy containing rare earths (such as Nd--Fe--B or Sm--Co) or other materials. Like the yoke, the pole pieces are made of soft magnetic material, for example steel.
Between the magnets or the pole pieces and the armature is the air gap, the thickness of which must be as limited and as uniform as possible. In mass produced motors it is usually on the order of 0.6 to 1 mm. It is difficult to have a smaller thickness, particularly due to the fact that the yoke, which the magnets, possibly with their pole pieces, lean against, is generally made of rolled or drawn steel and has a geometric irregularity, due to dimensional and symmetrical tolerances, which is cumulative with that of the other components.
In order to produce this result, it is necessary to subject the magnet to a careful and costly machining. This machining requires great care, particularly when the magnet is made of sintered material.
However, it is sometimes possible to produce air gaps with a thickness reduced to 0.3 mm by taking precautions in both the machining and the assembly of the various components of the inductor, precautions which are often difficult to carry out and lead to a substantial increase in cost.
The magnets are usually attached inside the yoke by means of removable clamps or pins, by being held in a non-magnetic casing (for example, made of plastic), by welding or by injection of a non-magnetic resin.
It is also known, and advantageous for achieving the mounting of the magnets, to embody a rigid piece comprising machined magnets (possibly with their pole pieces) over-molded with a non-magnetic material, for example aluminum or a thermosetting resin. The rigid assembly is then easily introduced and positioned in the yoke; it can also be obtained by over-molding the magnets directly in the yoke.
In any case, the magnets are in contact with the yoke, or with equivalent pieces, made of soft ferromagnetic material, so as to ensure a continuous circuit of magnetic flux between the magnets, which is essential to the operation of the motor.
One solution of this type is known from the patent FR 2617344. Composite magnets (4), possibly associated with additional pole pieces, wherein the profile of the pole face is adapted and concentric to the armature, produced from a Nd--Fe--B powder mixed with a binder or compacted, are in contact with the yoke (1) and are possibly associated with additional pole piece
REFERENCES:
patent: 3899702 (1975-08-01), Hanna et al.
Dougherty Thomas M.
Mullins B.
Ugimag SA
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