Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-01-18
2004-08-10
Ponomarenko, Nicholas (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S045000, C310S215000, C174S12000C, C029S596000
Reexamination Certificate
active
06774511
ABSTRACT:
This invention relates to a rotary electrical machine of the type which comprises a rotor and a stator on which electrical windings are formed.
The invention also proposes a method of making a rotor and a stator for a rotary electrical machine.
As is known, rotary electrical machines comprise a rotor and a stator on each of which an electrical winding may be formed.
The rotary electrical machine may be an alternator which converts rotary motion of the rotor into an electric current. The electrical machine may also be a motor which converts an electric current flowing through a winding of the rotor into rotational movement of the is rotor. The machine can be reversible and can thereby convert mechanical energy into electrical energy and vice versa.
Each electrical winding consists of a winding of at least one electrically conductive element which is coated with a layer of electrically insulating material. In transverse cross section, a winding is thereby formed in which portions of the electrically conductive element are juxtaposed horizontally and vertically.
As is known, the stator of a rotary electrical machine comprises a body which is provided with a set of axial or helical internal slots open radially and open axially. Such slots can be seen for example in the document FR-A-2 603 429 (U.S. Pat. No. 4,908,541). Conventionally, the body is of metal and consists of a stack of metal laminations. Each slot receives a set of portions of one or more conductive elements of a coil of a stator winding. The coil includes axial strands which are received in the slots and which are joined together by transverse strands in the form of loops which constitute heads of the winding, which are also called wings.
In general, the alternator is of the three-phase type, and the stator has three windings. In another version the alternator is of the six-phase type.
During manufacture of the stator, the axial strands of the coated conductive elements are compressed transversely within the slots, so that they fill the latter more fully, and they are then held in position by means of a slot closure element, for example.
In order to ensure optimum functioning of the rotary electrical machine, it is preferable that the winding should, with the stator, form a sufficiently rigid block, in particular to limit vibrations and noise, and to do so throughout the whole working life of the rotary electrical machine. The block must however be flexible enough to limit magnetic noise.
The known manufacturing method consists in impregnating the winding thus formed with a varnish, so as to stiffen it and to join it to the stator.
The impregnation can be obtained by immersing the stator in a bath of varnish, or by causing varnish to flow over and between the axial and transverse strands.
In order to cause the varnish to set, the stator which is equipped with the winding is heated in a stove to a sufficiently high temperature.
However, the viscosity of the varnish, and the contact between certain portions of the strands of the winding, do not permit the varnish to fill in an optimum manner some of the interstice that exist.
Such a method has a number of drawbacks.
The partial impregnation of the winding does not allow the conductive elements to form a rigid enough block. The mechanical and vibrational strength of the stator is not optimised. In consequence, the noise emitted by the machine is not minimal.
The said method is long, as the impregnation of the winding and setting of the varnish lasts for several tens of minutes. In addition, the method is difficult to control and calls for expensive installations such as stoves which consume large quantities of energy. It also causes polluting vapour to be emitted, especially during heating of the varnish.
The dimensional tolerances in the stator, especially in the wings, are large. In this connection, the positioning of the transverse strands of the electrically conductive element is not correctly controlled. They can shift between the instant at which the axial strands are received in the slots in the stator body, and the instant at which the varnish becomes set. It is therefore necessary to provide large operating clearances around the wings of the stator, so that, firstly, the transverse strands will not rub on the carcass of the rotary electrical machine, which would cause wear in the insulating layer and then a short circuit, and secondly, any risk of fracture of the transverse strands by the rotor during its rotation is avoided.
The movement of the transverse strands also causes the density of the wings to be reduced.
In order to reduce the risk of short circuit between the conductive element and the stator body, a leaf of electrically insulated material is interposed between each wall that defines a slot and the adjacent axial strands of the conductive element that lie in that slot.
The reduction in the risk of short circuiting between the conductive element and the stator body can also be obtained by means of a protective layer such as an epoxy layer. This protective layer is interposed between each wall that defines a slot and adjacent axial strands of the conductive elements situated in that slot.
In order to ensure good mechanical and vibrational strength in the winding, it is preferable that it be immobilised with respect to the stator body, that is to say the leaf of insulating material should be joined to the wall which defines the slot and to the axial strands with which it is in contact. Thus, in general, holes are formed in the leaf in such a way as to enable varnish to pass through them so as to infiltrate between the wall defining the slot and the insulating leaf.
Heating of the stator hardens the varnish, and consequently immobilises the insulating leaf with respect to the axial strands with which it is in contact, and with respect to the slot.
However, it frequently happens that the amount of varnish which enables these joints to be made, especially that which infiltrates between the wall defining the slot and the insulating leaf, is insufficient to ensure fastening of those elements. The vibrations set up by their movement with respect to the stator body increases noise in the rotary electrical machine and reduces its output.
Where the quantity of varnish is insufficient between the wall defining the slot, the leaf of insulating material and the conductive element, heat transfer is reduced, which causes the output of the rotary electrical machine to be reduced.
On the other hand, where there is too much varnish, the general stiffness of the wires with the stator body is not optimum, and this results in magnetic noise induced by the magnetic forces.
In addition, the stiffness of the varnishes currently employed varies with temperature. Thus, the higher the temperature of the varnish, the weaker is the magnetic noise emitted by the rotary electrical machine.
In consequence, the known method does not permit manufacture of a stator which ensures optimum operation of the rotary electrical machine.
The winding of the rotor of the rotary electrical machine is generally formed in a winding body of electrically insulated plastics material, which consists of an annular element having a U-shaped axial half section as can be seen for example in
FIG. 1
of the document FR-A-2 603 429 mentioned above.
The winding body guides the electrical conductive element while it is being wound. However, it frequently happens that the transverse wings of the winding body move slightly apart, thereby causing poor winding. The electrically conductive element can take the form of transverse wings overlaid with petals. During transport before impregnation of varnish, there can also occur partial radial displacement of certain portions of the electrically conductive element of the winding which moves the flanks of the winding body apart and causes it to become wider. Thus, when the winding is to be interposed between the two pole wheels, this widening effect is compacted, which involves the danger of destruction of the electrically insulating coating, in particular that of the
Chochoy Jean-Pierre
Framery Francis
Laxenaire Arnaud
Aguirrechea J.
Liniak Berenato & White
Ponomarenko Nicholas
Valeo Equipements Electriques Moteur
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