Abstract:
A method for making a wire-wound rotating part for an electrically driven machine, wherein a sheet metal pack and a commutator spaced therefrom are attached to a shaft, and conductive strands are wound around the sheet pack and the commutator to form a generally ring shaped winding. The method further comprises axially compressing the winding and simultaneously moving the commutator closer to the sheet pack. The method is particularly useful for making electric fans for motor vehicles.

Description:
FIELD OF THE INVENTION 
     The invention relates to a rotating part of an electrically driven machine, a direct-current motor for a motor vehicle comprising such a rotating part and a method for making such a rotating part. 
     BACKGROUND OF THE INVENTION 
     Direct-current motors for electric fans in motor vehicles are known which comprise an inductor with permanent magnets and a wire-wound armature. This armature has a support and a generally ring-shaped winding formed of strands wound around the support. The circulation of a current in the strands placed in the magnetic field generated by the inductor gives rise to a Laplace force in the strands which causes the rotation of the armature around its axis. The strands comprise rectilinear sections, parallel to the axis of the armature, and at the end thereof intermediate sections connected to the commutator or to another rectilinear section. The Laplace force essentially occurs only in the rectilinear sections. 
     The inactive intermediate sections are disposed and fitted together at the axial end faces of the winding to occupy a reduced space. These thus form bulges called armature leading-out wires. The spatial requirement of the leading-out wires in the axial direction of the motor is large, and may be equal to the length of the active rectilinear sections. The axial spatial requirement of the motor itself therefore depends to a great extent on the axial spatial requirement of the leading-out wires. In the motor industry, inter alia, there is today an increasing demand for motors having a reduced axial spatial requirement. 
     Moreover, the dimension of the winding in the axial direction, which is large, is matched with a tolerance range which is itself large. It follows that the parts of a motor adjacent to the winding occupy positions which take this tolerance range into consideration. The axial spatial requirement of the motor is therefore doubly increased. 
     Furthermore, the volumetric distribution of the strands parallel to the axes and of the leading-out wires is generally irregular. This poor distribution creates a weight imbalance or mass imbalance, which it is necessary to compensate by rebalancing the armature after production before mounting in the motor. This compensation forms an operation which becomes increasingly delicate as the initial lack of balance increases. 
     One problem is therefore of providing a method for producing a wire-wound rotating part having leading-out wires which have a reduced axial dimension and a reduced tolerance range associated with this dimension, and distributed more regularly than the leading-out wires of the above-mentioned rotating parts. 
     From the prior art, particularly the English translation of the abstract of the Japanese patent JP-4 275 050 (Fujitsu General Ltd), the production of a wound stator having a reduced axial dimension is known by winding the strands onto the sheet metal pack, then disposing the sheet metal pack with its winding in a press comprising two clamping jaws having opposite coaxial annular compression faces. The first clamping jaw has a core onto which the sheet metal pack with its winding is threaded. When the press is closed, the end of the core penetrates into a cavity of the second clamping jaw intended for this purpose. Then the two clamping jaws are brought closer to one another to perform the axial compression of the winding. 
     Thus, the compression force causes the crushing of the leading-out wires in the axial direction and brings about a great reduction in the axial spatial requirement of the winding. 
     However it is known that to produce the wire-wound rotating part of an electrically driven machine, it is advantageous to proceed as follows: 
     attach a bare sheet metal pack onto a shaft; 
     then fix a commutator onto the shaft in a temporary position spaced from the sheet metal pack; 
     then wind the strands simultaneously onto the sheet metal pack and the commutator; and finally 
     bring the commutator closer to the sheet metal pack to place it in its permanent position. 
     This method facilitates the production of the winding. The teaching of the abstract of the above-mentioned Japanese document cannot be used in these conditions, as it relates to a winding of a fixed part of an electrically driven machine which is provided with neither a shaft nor a commutator. 
     One object of the invention is to propose a method for producing a rotating part of an electrically driven machine enabling the winding to be produced simultaneously on the sheet metal pack and on the commutator in the temporary position before placing the commutator in the permanent position, whilst obtaining the above-mentioned advantages of the axial compression of the winding. 
     SUMMARY OF THE INVENTION 
     With a view to the achievement of this object, according to the invention there is specified a method for producing a wire-wound rotating part for an electrically driven machine, including stages consisting of: 
     attaching a sheet metal pack and a commutator onto a shaft, the commutator being spaced from the sheet metal pack; and 
     winding conductive strands onto the sheet metal pack and the commutator to form a generally ring-shaped winding, 
     the method also including the step consisting simultaneously of compressing the winding in an axial direction of the winding, and bringing the commutator closer to the sheet metal pack. 
     Thus, the temporary position of the commutator facilitates the production of the winding on the commutator and sheet metal pack. Moreover all the advantages of the axial compression of the winding are obtained. Furthermore, certain strands have an end connected to the commutator and another end connected to the axial end face of the winding directed towards the commutator. During the axial compression of the winding simultaneously with the displacement of the commutator, the two ends of these strands are displaced in the same direction in the axial direction of the shaft. Consequently, between these two ends no traction occurs which is likely to alter or break the strand, and the excess of strands adjacent to the commutator does not produce any masses from which short circuits could result. The risk of contact, or shocks, between the strands is reduced. This method generally enables the deterioration of the insulating sheath or of the insulating varnish of the strands to be avoided to a great extent during compression, which deterioration could in the opposite case cause short circuits between the strands. In particular, the crushing of the strands which could cause the cutting of some of them is avoided. 
     The method advantageously includes during compression the phase consisting of guiding strand sections extending from the commutator to the sheet metal pack. 
     Thus the above-mentioned drawbacks are further avoided, for the strands adjacent to the commutator, i.e. the formation of masses, their crushing or their excessive traction, from which a contrario the alteration of the insulating material of the strands and short circuits between them could result. 
     The guiding phase advantageously includes the operation consisting of keeping each of the said strand sections in a fixed radial plane determined in relation to the shaft. 
     It involves a particularly simple manner of producing this guidance. 
     Conductive strands having an outer sheath made of thermosetting material are advantageously wound onto the support, and during the compression stage the winding is heated to a temperature at least equal to the setting temperature of this material. 
     Thus the strands are immobilised in the compression position of the winding. Therefore the service life of the obtained arrangement of the strands is prolonged. 
     The winding is advantageously heated by circulating electric current in the strands. 
     Thus it is not necessary to use a press equipped with its own heating means. 
     Before the compression stage, a hot liquid substance which can harden on cooling is advantageously applied onto the strands, and the compression stage is extended until the cooling of the substance. 
     It involves another manner of obtaining the immobilisation of the strands in the compressed position. 
     The invention also relates to a press for the production of a wire-wound rotating part for an electrically driven machine, the press comprising a first clamping jaw and a second clamping jaw having respective compression faces having a general ring-shape in plan view, coaxial to one another and extending opposite one another, the press being designed to move the two clamping jaws relatively in the axial direction of the compression faces, each clamping jaw having a cavity in the centre of the compression face, with at least the first clamping jaw having a generally ring-shaped bearing face in plan view, coaxial to the compression face, having a larger diameter which is less than a smaller diameter of the compression face, and forming a base of the cavity. 
     This press enables the method according to the invention to be used. This press may ensure in particular the compression of the winding by the direct contact of the compression faces with the axial end faces of the winding. 
     The cavity having the bearing face may receive the commutator, the bearing face stressing the commutator for its displacement from its temporary position to its permanent position. 
     The second clamping jaw advantageously has a generally ring-shaped bearing face, coaxial to the compression face, having a larger diameter which is less than that of the bearing face of the first clamping jaw and forming a base of the cavity associated with the second clamping jaw. 
     This cavity may receive the end of the shaft opposite the commutator. Thus, the displacement of the commutator is performed by stressing the commutator, on the one hand, and the axial end of the shaft opposite the commutator, on the other hand, towards one other in the axial direction. For the displacement of the commutator it is therefore not necessary to further stress the axial end face of the winding opposite the commutator. 
     At least one of the clamping jaws advantageously has at least one contoured edge which is ring-shaped in top view, prolonging the compression face and protruding therefrom towards the other clamping jaw, the edge having a contour like the sector of an ellipse or of a parabola, the compression face having a rectilinear contour touching a vertex of the ellipse or of the parabola. 
     During compression, this edge ensures the guidance of the peripheral strands adjacent to the axial end faces of the sheet metal pack. The ellipse-shaped or parabola-shaped contour enables this guidance to be performed by reducing as far as possible the risks of crushing the strands. 
     The edge is advantageously prolonged by another curved contour, the junction between the two contours forming a point of inflection. 
     Thus, one can avoid producing a protruding edge at the end of the guide contour. 
     The press advantageously comprises stop means designed to limit the relative displacement of the clamping jaws towards one another to prevent the relative moving together of the compression faces within a predetermined distance. 
     Thus any excessive compression of the winding is prevented, from which an irreversible alteration of the strands could result. 
     The stop means advantageously comprise plane stop faces on the clamping jaws, roughly perpendicular to the axis, and designed to come into contact with one another. 
     The press advantageously comprises at least one series of bulges designed to be disposed in the vicinity of the cavity and protruding from a plane of the compression face of the first clamping jaw towards the second clamping jaw, the bulges being disposed roughly in a circle coaxial to the cavity, regularly around the axis. 
     Thus during compression these bulges ensure the guidance of the strands connected to the commutator which was involved above. 
     The bulges are advantageously borne by the first clamping jaw. 
     The press advantageously comprises a slide which can move by sliding through the first clamping jaw in relation thereto, in the axial direction, the slide bearing the bulges. 
     Thus the position of the bulges may be changed at will (for example to make the bulges protrude more or less) during the various compression phases and/or as a function of the configuration of the produced rotating part. 
     At the least the compression faces are produced from steel, these faces having undergone a superficial treatment such as case hardening, nitride hardening or carbonitriding. 
     In fact it is advantageous for the clamping jaws to have a certain superficial hardness, for example 55 to 60 HRC (Rockwell) and also good sliding properties, and also a good surface state, to avoid harming the strands during the compression. 
     Furthermore according to the invention there is specified a wire-wound rotating part for an electrically driven machine which was produced by means of the method specified by the invention. 
     Furthermore according to the invention there is specified a wire-wound rotating part for an electrically driven machine, comprising a shaft, a sheet metal pack and a commutator attached to the shaft, and a generally ring-shaped winding comprising conductive strands wound onto the sheet metal pack and commutator, the rotating part comprising at least one series of elongated pins disposed in a circle coaxial to the shaft regularly around the shaft, the pins being oriented in a direction roughly opposite to the sheet metal pack and being designed to be interposed radially between the commutator and the winding. 
     Thus, guide bulges of the strands adjacent to the commutator are borne by the rotating part itself, as a replacement or as a supplement to those borne by the press. 
     The rotating part advantageously comprises a washer threaded onto the shaft and bearing the pins. 
     The washer may more particularly be placed in the axial direction between the commutator and the winding, and even attached to the commutator. 
     The rotating part advantageously comprises an insulating plate integrated in the sheet metal pack parallel thereto and bearing the pins. 
     The plate may be the insulating cheek or star disposed, as is known, at each end of the sheet metal pack before the production of the winding. 
     The strands are advantageously glued to one another by means of a material applied to the strands. 
     It advantageously relates to a direct-current motor armature for a motor vehicle. 
     It advantageously relates to an armature for an electric fan. 
     Furthermore in accordance with the invention a direct-current motor for a motor vehicle comprising a rotating part as specified by the invention is specified. 
    
    
     BRIEF DESCRIPTION OF THE FIGURE 
     Other characteristics and advantages of the invention will also become apparent in the following description of a preferred embodiment and of refinements given by way of non-restrictive examples. In the attached drawings: 
     FIG. 1 is a view in axial section of a motor comprising an armature according to a preferred embodiment of the invention; 
     FIGS. 2 and 3 are views in axial section of the rotating part of FIG. 1 during production showing two stages of the utilisation of the method according to a preferred embodiment of the invention; 
     FIG. 4 is a principle view in axial section of a press according to the invention for the utilisation of the method of FIGS. 2 and 3; 
     FIG. 5 is a partial view on an enlarged scale of detail D of FIG. 4, showing the first clamping jaw only; 
     FIG. 6 is a detailed sectional view similar to FIG. 4, showing the first clamping jaw only; 
     FIG. 7 is an underneath view of the clamping jaw of FIG. 6 showing just the arrangement of the bulges; 
     FIG. 8 is a view similar to FIG. 6, of the first clamping jaw and of the rotating part, showing a first refinement; 
     FIGS. 9 to  10  are views similar to FIGS. 2 and 3 showing a second refinement; 
     FIG. 11 is a plan view of a cheek used in the second refinement of FIGS. 9 and 10; 
     FIGS. 12 and 13 are views similar to FIGS. 2 and 3 showing a third refinement; and 
     FIG. 14 is a partial view in longitudinal section of a strand of the motor of FIG. 1, according to a fourth refinement. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 presents a direct-current motor  2  of an electric fan for a motor vehicle. This motor comprises a fixed casing  4  and permanent magnets  6  attached internally to the casing, the casing and the magnets forming an inductor of the motor. The motor also comprises an armature  8  according to the invention forming the rotating part of the motor. The armature  8  is produced according to the method which will be described below. 
     With particular reference to FIGS. 1 and 2, an armature support  14  is produced by disposing generally circular sheets  13  parallel to one another, concentrically against another. Thus a generally axially cylindrical sheet metal pack  12  is formed. These sheets have outer radial openings forming, by the fitting together of the sheets, recesses (not represented) having a base parallel to the axis  12  of the cylinder. To the sheet metal pack is attached a shaft  10  passing through the sheet metal pack along its axis  12 , and to the shaft  12  is attached a commutator  16  in a temporary position spaced from the sheet metal pack, as on FIG.  2 . 
     Then strands  9  are wound onto the sheet metal pack and the commutator  16  so as to produce a generally ring-shaped armature winding. Each strand  9  comprises a copper wire and an insulating sheath covering the wire. The strands  9  are more particularly engaged in the radial recesses of the sheet metal pack. The strands thus comprise rectilinear sections parallel to the axis  12 , extending into the recesses and intended to cause the rotation of the armature when a current passes through the strand, under the field effect created by the inductor. The strands  9  also comprise curved inactive sections, extending to the ends of the active rectilinear sections, and linking the rectilinear sections to one another, or to the commutator, or forming ends of the strands. The curved inactive sections are assembled and entwined to form armature leading-out wires defining two opposite axial end faces  15  of the winding. On each end face, the leading-out wires have a generally ring-shaped arrangement of axis  12 . Some of the strands  9  have a first end fixed to the commutator  16 , for example by welding, and a second end fixed to an axial end face  15  of the winding directed towards the commutator  16 . 
     A following step of the method uses a press according to the invention such as that in FIGS. 4 to  7 . 
     The press comprises a first clamping jaw  23  and a second clamping jaw  24  made of steel. The first clamping jaw  23  has a plane compression face  28  which is generally ring-shaped in plan view, having a rectilinear contour. The clamping jaw  23  has two edges  30 , an outer and an inner edge respectively adjacent to the outer and inner circumferences of the compression face  28 . Each edge  30  is generally ring-shaped in plan view and has a curved contour having two contour zones  30   a,    30   b,  having curves directed in opposite directions, as can be seen on FIG.  5 . The first contour zone  30   a  has the general shape of a sector of an ellipse or of a parabola. This zone  30   a  is disposed so that the rectilinear contour of the compression face  28  touches the parabola or the ellipse at a vertex S thereof, if necessary, the vertex of the ellipse being here regarded as an end of the major axis of the ellipse. Thus the first contour zone  30   a  by one end prolongs the rectilinear contour of the compression face  28 . The second contour zone  30   b  extends in the prolongation of the other end of the first contour zone  30   a,  the junction between the two contour zones being formed by a point of inflection I. The second contour zone  30   b  is also shaped as a sector of an ellipse or of a parabola. When the first or the second contour zone is shaped as a sector of an ellipse, this sector is less than or equal to one quarter the circumference of the ellipse. 
     The first clamping jaw  23  has a cylindrical lateral face  34  extending from the other end of the second contour zone  30   b  associated with the outer edge  30 . The cylindrical face  34  is coaxial to the compression face  28  and parallel to its axis. The first clamping jaw  23  has a plane annular stop face  36  parallel to the compression face  28 , extending from the cylindrical lateral face  34 , towards the exterior of the jaw, whilst being locally perpendicular to this cylindrical face  34 . The first clamping jaw  23  has a central cylindrical face  38  coaxial to the compression face  28 , parallel to its axis and defining a cavity  39  in the centre of compression face. The junction between the cylindrical face  38  and the inner edge  30  is formed by a rounded contour. The inner edge  30  extends protruding from the plane of the compression face  28  of this clamping jaw, in the direction of the other clamping jaw  24 . The first clamping jaw  23  has a plane ring-shaped bearing face  40 , parallel and coaxial to the compression face  28 , adjacent to the central cylindrical face  38 , having a larger diameter, or external diameter, which is less than the diameter of the internal circumference of the compression face  28  (or smaller diameter thereof) defining a base of the cavity  39 . 
     For the preceding characteristics, the second clamping jaw  24  is identical in shape and in dimensions to the first clamping jaw  23 . 
     The first clamping jaw  23  also has a cylindrical conduit  42  extending from the base  40  of the cavity  39 , coaxially to the compression face  28 . The second clamping jaw  24  in turn has a blind counterbore  44  extending from the base  40  of the associated cavity, coaxially to the compression face  28 . In particular, the blind counterbore  44  has a ring-shaped bottom face  45 , preferably disc-shaped, having a larger diameter which is less than that of the base  40  of the cavity  39  of the first clamping jaw  23 . 
     The two clamping jaws  23 ,  24  are disposed with their compression faces  28  coaxial, opposite one another and spaced from one another. 
     The press comprises conventional means known per se such as jacks designed to displace one of the clamping jaws, for example the first clamping jaw  23 , parallel to the axial direction in relation to the other jaw, for example the second fixed clamping jaw  24 . The two stop faces  36  of the clamping jaws are designed to come into contact with one another to form stop means which limit the relative displacement of the clamping jaws towards one another to prevent the relative bringing together of the compression faces  28  within a predetermined distance. 
     With reference to FIGS. 6 and 7, the inner edge  30  of the first clamping jaw  23  comprises a series of elongated bulges  46 , having rounded contours and extending projecting from this edge towards the second clamping jaw  24 , in the vicinity of the cavity  39 . The bulges  46  are disposed roughly in a circle coaxial to the compression face  28 , regularly around the axis. The direction of elongation of the bulges  46  is radial to the axis. 
     All the above-mentioned faces of the clamping jaws have undergone a surface treatment such as case hardening, nitride hardening or carbonitriding, with a view to endowing them with great hardness, for example 55 to 60 HRC (Rockwell) and a good surface quality. 
     The press is used in the following manner. 
     With the press open and the first clamping jaw  23  spaced from the second clamping jaw  24 , the wire-wound rotating part is placed in the press so that it us is situated at the end of the winding stage. For this, the rotating part is placed in the press and coaxially thereto. 
     The end of the shaft the furthest from the commutator  16  is housed in the blind counterbore  44  of the second clamping jaw  24 , the winding resting by its lower axial end face  15  on the compression face  28  of the second clamping jaw  24 . When the press is then closed again, the commutator  16  occupies the cavity  39  of the first clamping jaw  23 , at a distance from the base  40  thereof, the shaft end adjacent to the commutator  16  extending into the conduit  42  of the first clamping jaw. The stop faces  36  of the clamping jaws are spaced from one another. The compression face  28  of the first clamping jaw  23  is in contact with the upper axial end face  15  of the winding. 
     Then the press is actuated. The first clamping jaw  23  moves closer to the second clamping jaw  24  by sliding, the compression faces  28  producing the compression or compacting of the winding directly on the axial end faces  15  of the winding which are stressed in the axial direction towards one another. 
     During this axial compression, the strands  9  extending at the periphery of the winding in the vicinity of the axial end faces  15  come into contact with the outer and inner edges  30  of the clamping jaws, as on FIG.  5 . Thanks to the above-mentioned shape of the contour of these edges, the strands coming into contact with these edges are guided along the edges in the direction of the axis of the clamping jaws. These edges  30  thus ensure a compression or compacting of the axial end faces  15  of the winding in the radial direction, in the direction of the axis. This radial compression is performed without altering the strands. 
     At the same time as the compression of the winding occurs, the base  40  of the cavity of the first clamping jaw  23  comes to rest in the axial direction against the upper face of the commutator  16  and stresses it towards the sheet metal pack. The base  45  of the blind counterbore  44  of the second clamping jaw  24  stresses the end of the shaft opposite the commutator in the axial direction, in the opposite direction. The moving together of the clamping jaws brings about the displacement of the commutator  16  along the shaft to a permanent position closer to the sheet metal pack than the previous temporary position. 
     At the same time as this compression of the winding and this displacement of the commutator, the strands  9 , which have one end connected to the commutator  16  and one end connected to the axial end face  15  of the winding adjacent to the commutator, come into contact with the bulges  46  and are inserted between the bulges  46  as the first clamping jaw  23  draws closer to the second clamping jaw  24 . During the entire sequence of this moving together, these strands remain between the bulges  46  and are thus each held and guided in a determined fixed plane radial to the shaft of the rotating part. Thus clusters, shocks between strands and the crushing of said strands are avoided, these strands having a slack configuration after winding and before compression. The inner edge  30  of the first clamping jaw enables the strands adjacent to the commutator to be tightened. 
     At the end of the compression, the press is opened and the first clamping jaw is again moved away from the second clamping jaw. The rotating part is removed. With reference to FIG. 3, the winding has axial end faces  15  which are substantially plane. The edge zones of these faces have a male shape complementary to the female shape of the outer and inner edges  30  of the clamping jaws. 
     In a refinement represented in FIG. 8, the press comprises a slide  60  which can move by sliding in the axial direction, in relation to the first clamping jaw  23  and through it. The slide  60  comprises a crown  62  having a series of bulges  64  disposed regularly over a circle coaxial to the axis and inscribed in a plane perpendicular to the axis. The slide  60  is designed to be moved so that the bulges  64  can occupy a position in which they extend protruding from the inner edge  30  of the first clamping jaw  23  towards the second clamping jaw  24 , and a position in which they are on the contrary pushed back in relation to the plane of the compression face  28  of the first clamping jaw. The slide  60  is for example designed so that the bulges  64  are movable in the cavity  39  of the first clamping jaw  23 , the bulges being adjacent to the central cylindrical face  38 . 
     This press may for example be used in the following manner. When the rotating part is positioned in the press, the bulges  64  are in the pushed back position. When the press is closed, the slide  60  moves to dispose the bulges  64  protruding from the edge  30  as mentioned above, which position the bulges retain during compression to ensure the guidance of the strands  9  as described previously for the bulges attached to the edge. Before opening the press, the slide  60  moves away from the second clamping jaw  24  to replace the bulges in pushed back position. 
     In the second refinement represented in FIGS. 9 to  11 , the sheet metal pack comprises, as is well known, two insulating plates  66  made of plastics disposed at the ends of the sheet metal pack, parallel to the other sheets. Such plates are sometimes called “cheeks” or “stars” and have a slot identical to that of the other sheets, in particular a central circular opening  68  and recesses  67  for the passage of the strands of the winding. 
     In the present refinement, the cheek  66  intended to be the closest to the commutator  16  has a series of pins  70  extending from the edge of the central opening  68  whilst being regularly distributed around the axis of the plate. The pins  70  have an elongated rectilinear shape in the radial direction towards the axis and extending protruding from one face of the cheek. Said cheek is disposed in the sheet metal pack so that the pins  70  are orientated in the direction of the commutator  16  and in the opposite direction to the sheet metal pack. They thus have a shape like a truncated cone. The winding is produced so that the free end of each pin  70  extends roughly in the general plane of the corresponding axial end  15  of the winding. 
     During compression in the press, these pins  70  ensure the guidance of the strands  9  connected to the commutator  16 , as described above. At the end of compression, bearing in mind the permanent position of the commutator  16 , the pins  70  are situated placed radially between the commutator  16  on the one hand and the winding and the sheet metal pack on the other hand. 
     In the third refinement represented in FIGS. 12 and 13, the rotating part this time comprises a washer  72  made of plastic material, coaxial to the commutator  16  and attached thereto so that once the commutator is threaded onto the shaft, the washer  72  is placed in the axial direction between the commutator and the sheet metal pack. The washer  72 , like the commutator  16 , is threaded onto the shaft  10 . The washer comprises a plane ring-shaped washer body, and pins  74  protruding from an outer circular circumference of the washer body and of a face of this body. 
     The pins  74  are elongated in a direction radial to the shaft and oriented in the opposite direction to the axis of the washer. The washer is disposed so that the pins  74  extend from the side of the commutator  16 , the total diameter of the washer at the level of the pins being greater than the diameter of the commutator. During winding, the strands  9  adjacent to the commutator  16  are inserted between the pins  74 . 
     During compression, the washer  72  is moved as a unit with the commutator  16 . The pins  74  are responsible for guiding the above-mentioned strands  9  as described above. 
     In the fourth refinement represented in FIG. 14, the sheath  13  of the strands is formed by a thermosetting and electrically insulating material. By thermosetting is understood, as is well known, a material having a certain flexibility in the unworked state and which, when it is heated to a temperature at least equal to a predetermined threshold characteristic of the material, becomes rigid, even after cooling. 
     In this refinement, during the compression stage, an electric current is circulated in the strands  9  by supplying the commutator  16  in a modified manner. This current is chosen so it has an intensity adequate to heat the winding by JOULE effect to a temperature equal to or greater than the hardening temperature of the material forming the sheath  13 . The strands  9  are thus supplied until the polymerisation of the material is obtained, from which its hardening results. 
     From that time onwards the supply of the strands with electric current ceases, and the compression is stopped by opening the press. As the material of the sheathes  13  has hardened, no significant spring-back of the winding, in particular of the leading-out wires, is produced, along the axis  12  by the spring effect. The sheathes  13  keep the leading-out wires crushed in the compression position. 
     At the end of the method according to the invention in the above-mentioned embodiment and the refinements, the axial end faces  15  of the winding are plane and perpendicular to the axis  12 . They may have cavities between certain crushed leading-out wires. As these faces are formed by the crushed leading-out wires, they have on the millimeter scale an irregular appearance caused by the strands  9  pressed against one another. The axial dimension of the winding has thus been reduced. Moreover, the tolerance range to be associated with this reduced dimension d′ of the winding may itself be substantially reduced in relation to the range attached to the axial dimension d before compression. The reduction in the tolerance range will be, for example, equal to the reduction n the axial dimension, i.e. d−d′. The saving in space achieved will therefore be equal to the sum of the reduction in the axial dimension and the axial reduction in the tolerance range, i.e. 2×(d−d′). The saving in space is therefore equal to twice the axial reduction performed on the leading-out wires. This saving in space has repercussions on the position of the parts of the motor in FIG. 1 adjacent to the end faces  15  of the winding, and enables the axial dimension of the motor to be reduced. 
     Moreover, the crushing of the leading-out wires improves the volumetric distribution of the strands and of the leading-out wires in the sense of greater regularity. 
     The method according to the invention therefore enables the unbalanced mass of the rotating part to be further reduced. 
     Of course, numerous modifications could be made to the invention without departing from the scope thereof. 
     The strands  9  could be heated during compression without providing them with current, thanks to adapted heating means. 
     Moreover strands comprising a sheath made of a conventional insulating material could be used, and to the strands a hot liquid substance which sets on cooling, such as a resin or a lacquer, could be applied before the compression stage. Then the compression of the winding is performed as mentioned above, without heating the winding and the compression stage is prolonged until the substance cools. Once it has cooled and therefore hardened, compression is brought to an end. The armature will consequently comprise strands stuck to one another by means of this material applied to the strands. 
     The invention is applicable to rotating parts of electric machines such as alternating-current motors, alternators or dynamos. 
     The term “compression load” will be understood in the broad sense, as covering any stress on at least one axial end face of the winding in relation to the other face with a view to its crushing. In particular, the compression will be able to be progressive or abrupt. 
     The above-mentioned embodiment and the refinements could be advantageously combined with respect to their compatible characteristics.