FIELD OF THE INVENTION

The present invention concerns electric rotating machines configured to be on board of an automotive vehicle, such as an electric vehicle (EV) or a hybrid vehicle (HV).

The present invention relates, in particular, to the rotor impregnation of an electric rotating machine.

BACKGROUND OF THE INVENTION

As is known, electric or hybrid vehicles comprise an alternating current (AC) electric motor. In general, the AC electric motor comprises a stator comprising stator windings, referring to a fixed part of the electric motor, and a rotor comprising rotor windings and a rotor shaft defined by a rotation axis, referring to a rotating part of the electric motor.

Impregnation of an object improves its physical properties and also tends to improve overall parameters of an equipment/component which uses the object. The rotor windings are thus impregnated with an impregnation medium in order, on one hand, to provide an improved electrical insulation and, on the other hand, to reduce vibrations of the rotor. Moreover, an impregnation of the rotor windings increases a thermal conductivity and thus improves a cooling efficiency of the rotor. Most frequently, the impregnation medium is a resin.

Generally, in order to impregnate the rotor windings in depth, the rotor windings are impregnated with the impregnation medium (e.g. resin) while the rotor is rotating around the rotation axis which is inclined. Otherwise, an achieved level of filling of the rotor windings may be insufficient. However, such an impregnation of the rotor windings may result in an undesired situation where some resin-free portions of the rotor are unintentionally filled with the resin, while a part of the rotor windings may not be properly impregnated.

In this context, improving the impregnation quality is the main objective of the present invention.

SUMMARY OF THE INVENTION

In accordance with the present invention a method for impregnating coils of a rotor with an impregnation medium is provided. The impregnation medium is preferably a resin. The rotor comprises a rotor shaft, a rotor core mounted on the rotor shaft, and the coils arranged in channels in the rotor core. The rotor core has a first end, and a second end which is opposite to the first end. The channels run along the rotor core from the first end to the second end. The method comprises positioning the rotor in a vertical position, such that the first end is located above the second end; applying, while the rotor is in the vertical position, an impregnation medium to the coils from the first end, such that the impregnation medium flows through the channels along the coils from the first end to the second end due to gravity; and hardening the impregnation medium, while applying it to the coils, at the second end only, in order to plug the second end by the hardened impregnation medium while allowing to fill up the channels with the impregnation medium.

Therefore, the method according to the present invention allows unimpregnated portions (where, for example, balancing holes are located) of the rotor can be entirely free from the impregnation medium. Furthermore, the design for mechanical strength is not restricted by the method according to the invention. In addition, while improving the impregnation quality, the manufacturing cost can still be reduced because compared to conventional methods for impregnating rotor coils, the present invention does not lead to a waste of an impregnation medium.

Moreover, while applying the impregnation medium, the rotor is preferably still so that the impregnation medium may be accurately applied onto the coils.

In particular, the rotor is part of an electrical machine, for instance, an electric motor, comprising a stator and the rotor being rotatable with respect to the stator about a rotation axis. While the rotor is in the vertical position, then the rotation axis extends along a vertical direction.

According to an embodiment, before applying the impregnation medium onto the coils, is positioned to be above at least one of the coils and not above any one of unimpregnated portions of the rotor core. The unimpregnated portions is arranged to be free from the impregnation medium.

In this way, the impregnation medium can be accurately applied only to the coils and would not wrongly drop into the unimpregnated portions.

Advantageously, the at least one medium feeder can be one or plural medium feeder; a number of medium feeders being determined according to a number of coils. The number of medium feeders can be equal to 1 or an integer smaller than or equal to the number of coils. The more medium feeders are used in the impregnating step, the less time is spent.

According to an embodiment, the method comprises, while applying the impregnation medium, a trickle impregnation configured to trickle the impregnation medium onto the coils according to a vertical and downward direction. The trickle impregnation allows a precise control over the quantity and flow of the impregnation medium.

According to an embodiment, the channels inside the rotor core are formed by coils separators of the rotor core.

Advantageously, the method further comprises hardening the entire impregnation medium after the entire channels are filled with the impregnation medium. The impregnation medium, before being hardened, is in liquid form.

Preferably, the method comprises hardening the impregnation medium by means of heating, in particular by heating the rotor by performing an induction heating or current heating. The impregnation medium is thus hardened.

According to an embodiment, the method comprises hardening the impregnation medium by using UV (ultraviolet) lights emitted to the second end, so as to cure the impregnation medium from the bottom to the top of the rotor core, wherein the UV lights are emitted by a UV light source located below the rotor core. Advantageously, the method comprises hardening the impregnation medium by performing an induction heating or current heating to cure a remaining part of the impregnation medium which is not successfully hardened yet after the above-mentioned UV curing step.

These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood on reading the description that follows, and by referring to the appended drawings given as non-limiting examples, in which identical references are given to similar objects and in which:

Figure 1 illustrates a side elevational view of a rotor before impregnation according to an embodiment of the invention;

Figure 2 illustrates a first end of a rotor core of the rotor according to an embodiment of the invention;

Figure 3 illustrates steps of a method for impregnating rotor coils of the rotor according to an embodiment of the invention. Figure 4 illustrates a side elevational view of the rotor in a vertical position according to an embodiment of the invention.

DETAILED DESCRIPTION

Several embodiments of the present invention will be detailed hereafter with reference to the drawings. It will be apparent to those skilled in the art from this present disclosure that the following description of these embodiments of the present invention are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

Figure 1 illustrates a side elevational view of a rotor 1 according to an embodiment of the invention. The three axis “x”, “y”, “z” in Figure 1 represent three dimensions of a space where the rotor 1 . The “x” and “y” axis define a horizontal plane. The “z” axis is a vertical axis of the space and is perpendicular to the horizontal plane. It is noted that the three axis “x”, “y”, “z” of Figures 2 and 4 have same definitions of those of Figure 1 .

The rotor 1 comprises a rotor shaft 13, a rotor core 14 and at least one rotor winding. The rotor shaft 13, defined by a rotation axis 1 11 , is parallel with the horizontal plane defined by the “x” and “y” axis of Figure 1 . The rotor core 14 is mounted on the rotor shaft 13, and has preferably a shape of cylinder. The rotor core 14 has a first end 141 and a second end 142 (which is opposite to the first end 141 ). A longitudinal length of the rotor core 14 is defined by a distance measured along with the rotation axis 11 1 and between the first 141 and the second 142 ends. The longitudinal length of the rotor core 14 is smaller than a total length of the rotor shaft 13.

According to the present invention, the rotor 1 comprises rotor windings forming a plurality of coils 22, for example the four rotor coils 22 as shown in Figures 1 , 2, and 4. The invention is nevertheless not limited to a number of rotor windings or to a number of coils 22 of the rotor windings. The coils 22, hosted in the rotor core 14, are arranged to radially surround the rotor shaft 13 and may be visible at the first end 141 , as depicted in Figure 2. Figure 2 illustrates the first end 141 of the rotor core 14. The coils 22 are configured to be impregnated with an impregnation medium. The impregnation medium is preferably a resin.

In addition to the coils 22, the rotor core 14 comprises unimpregnated portions 18 intended to be free from the impregnation medium. The unimpregnated portions 18 are at least partially visible at the first end 141 , as depicted in Figure 2. Some elements of the rotor 1 , being located in the unimpregnated portions 18, are free from being impregnated with or being filled with the impregnation medium. For example, the rotor 1 may comprise balancing holes arranged for positive balancing. The balancing holes are located in the unimpregnated portions 18 of the rotor core 14 so as to avoid being filled with the impregnation medium or other materials. Furthermore, the rotor core 14 comprises channels in which the coils 22 are arranged. The channels, running along the rotor core 14 from the first end 141 to the second end 142 of the rotor core 14, are configured such that the impregnation medium flows through the channels along the coils 22 from the first end 141 to the second end 142. The channels comprise each two open ends respectively located at one of the first and second ends 141 , 142 of the rotor core 14. According to an embodiment, the channels are formed by coils separators of the rotor core 14. The coil separators are formed together with the rotor core 14 by, for instance, an injection molding process.

At least one of the ends 141 and 142, preferably the second end 142, is covered by an end cover configured to prevent the impregnation medium from running out from the channels inside the rotor core 14.

Preferably, the coils 22 and the unimpregnated portions 18 are alternately distributed on the rotor shaft 13. Especially, the coils 22 and the unimpregnated portions 18 radially surround the rotor shaft 13.

Figure 3 illustrates steps 210 to 230 of a method 200 for impregnating the coils 22 of the rotor 1 with the impregnation medium according to an embodiment of the invention. The method 200 comprises positioning (step 210) the rotor 1 in a vertical position, such that the first end 141 is located above the second end 142, as shown in Figure 4. In this way, the rotor shaft 13 is in parallel with to “z” axis. Figure 4 illustrates a side elevational view of the rotor 1 in a vertical position according to an embodiment of the invention. In particular, the rotation axis 11 extends in a vertical direction while the rotor 1 is in the vertical position.

The first end 141 and the second end 142 are thus respectively a top end and a bottom end of the rotor core 14. The ends of the channels, respectively located at the first end 141 and the second end 142, are upper ends and lower ends of the channels.

The method 200 comprises applying (step 220), while the rotor 1 in the vertical position, the impregnation medium to the coils 22 from the first end 141 , such that the impregnation medium flows through the channels along the coils 22 from the first end 141 to the second end 142 due to gravity. Moreover, while applying the impregnation medium, the rotor 1 is preferably still so that the impregnation medium can be accurately applied onto the coils 22.

In addition, before applying the impregnation medium, at least one medium feeder 35 used to apply the impregnation medium, is positioned to be above at least one of the coils 22 and not above any one of the unimpregnated portions 18. In this way, the impregnation medium can be accurately applied to the coils 22 while keeping the unimpregnated portions 18 free from the impregnation medium. The impregnation medium would not wrongly drop into the unimpregnated portions.

A number of medium feeders 35 is determined according to the number of coils 22. The number of medium feeders 35 can be equal to 1 or an integer smaller than or equal to the number of coils 22. In an embodiment where only one medium feeder 35 is used, the coils 22 are impregnated with the impregnation medium one by one until all of the coils 22 are impregnated. In other words, each time it is necessary to precisely position the medium feeder 35 to be located above one of the coils 22.

In another embodiment where it is wished that the coils 22 are impregnated with the impregnation medium all at one time to save time, a plurality of medium feeders 35 are used, wherein the number of medium feeders 35 is equal to the number of coils 22. The medium feeders 35 are respectively positioned to be precisely located above one of the coils 22.

According to an embodiment, the method 200 comprises, while applying the impregnation medium, a trickle impregnation 221 configured to trickle the impregnation medium onto the coils 22 according to a vertical and downward direction 31 . The medium feeder(s) 35 are for example nozzle(s) 35 utilized to trickle the impregnation medium. The trickle impregnation 221 allows a precise control over the quantity and flow of the impregnation medium.

Alternately to the trickle impregnation 221 , the method 200 may comprise, while applying the impregnation medium, a flood impregnation performed in a way that the impregnation medium is then flooded in chamber(s) where the coils 22 are located. For example, the rotor is then closed and sealed by means of a bottom cover. Various types of resin can be used to perform the flood impregnation 222.

The impregnation medium, before being hardened, is in liquid form. The second end 142 of the rotor core 14 is, as mentioned above, covered by the end cover which prevents non-hardened impregnation medium from running out from the second end 142 (i.e. the bottom end of the rotor core 14 in the vertical position).

The method 200 comprises thus, hardening (step 230) the impregnation medium, while applying it onto the coils 22, at the second end 142 only, in order to plug the second end 142 by the hardened impregnation medium while allowing to fill up the channels with the impregnation medium. With the end cover which covers the second end 142, the impregnation medium at the second end 142 is firstly cured without running out from the second end 142. The cured impregnation medium plugs then the lower ends of the channels, which allows, on one hand, to prevent the impregnation medium from running out from the channels, on the other hand, to fill up the remaining channels up to the upper ends of the channels with the impregnation medium. The method 200 further comprises hardening the entire impregnation medium after the entire channels are filled with the impregnation medium.

According to an embodiment, the method 200 comprises hardening the impregnation medium by performing an induction heating or current heating to heat (step 231 ) the rotor 1.

According to an embodiment, the method 200 comprises hardening the impregnation medium by using UV lights 55 (step 232) emitted to the second end 142, so as to cure the impregnation medium from the bottom to the top of the rotor core 14, wherein the UV (ultraviolet) lights 55 are emitted by a UV light source located below the rotor core 14. The impregnation medium in the present embodiment must be curable through UV lights.

After the above UV curing step (step 232), it may still remain, probably in an upper portion of the channels of the rotor core 14, a remaining part of the impregnation medium which is not successfully hardened yet. The method 200 comprises thus hardening the impregnation medium by performing an induction heating or current heating to cure (step 233) the remaining part of the impregnation medium.

Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure.

The method for impregnating rotor coils according to the present invention provides multiple advantages regarding the manufacturing point of view. Without strict manufacturing requirements, the impregnation quality is also improved. For example, unimpregnated portions (where, for example, the balancing holes are located) of a rotor can be entirely free from the impregnation medium.

Furthermore, the design for mechanical strength is not restricted by the method according to the invention. In addition, the manufacturing cost can be reduced because compared to conventional methods for impregnating rotor coils, the present invention does not lead to a waste of an impregnation medium.