CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to International Patent Application No. PCT/EP2018/081527, filed on Nov. 16, 2018, and German Patent Application No. DE 10 2017 221 808.8, filed on Dec. 4, 2017, the contents of both of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to a method for producing a stator for an electric machine. The invention, furthermore, relates to a stator that has been produced by means of this method, and to an electric machine having such a stator.

BACKGROUND

Typically, conventional stators for electric machines comprise stator windings which, during the operation of the machine, are electrically energised. Such an electric machine can generally be an electric motor or a generator. The electric machine can be designed as external rotor machine or as internal rotor machine. During the operation of the machine heat is generated which, for avoiding overheating and damage or even destruction of the stator connected with this, has to be dissipated. To this end, it is known from conventional stators to equip the same with a cooling system for cooling the stator—in particular the said stator windings. Such a cooling system comprises one or more cooling passages, which are flowed through by a coolant and are arranged near the stator windings. By way of heat transfer from the stator windings to the coolant, heat can be dissipated from the stator. In this way, overheating of the stator windings and, connected with this, damage or even destruction of the stator, can be avoided.

In order to keep the production costs for providing the cooling passages mentioned above low it is known to overmould the core stacks of the stator forming the stator body including the stator teeth carrying the stator windings with a plastic mass and, during the course of the injection moulding operation, create the said cooling passages in the plastic mass. During the course of the overmoulding, the stator windings wound onto the stator teeth can be permanently fixed on the stator.

The fact that during the overmoulding of the stator body and of the windings arranged on the stator teeth it cannot be guaranteed that the windings formed so as to be electrically conductive do not lie against the—likewise electrically conductive—stator body, which are typically formed by electrically conductive shaped metal sheets that are stacked on top of one another proves to be problematic in this connection. The electrical connection between stator windings and stator body accompanied by this however causes an undesirable electrical short circuit.

This applies also for the case that is usual in practice that the stator windings are already produced with an electrical insulation, since these during the operation of the electric machine, because of high temperatures that can be caused by the high electric current flowing through the windings, can be partially damaged or even destroyed.

Likewise it cannot be excluded that the stator windings following the creation of the cooling passages by the injection moulding operation with plastic mass do not protrude into the cooling passages. In the event that the electrical insulation of the stator winding are damaged or even destroyed mentioned above, the stator windings can come into direct contact with the coolant conducted through the cooling passages, which has to be avoided in order to prevent an electrical connection of the stator windings with the coolant.

SUMMARY

It is therefore an object of the present invention to create an improved production method for producing a stator with cooling passages, with which the disadvantages mentioned above are largely or even completely overcome.

This object is solved through the subject matter of the independent claim(s). Preferred embodiments are subject matter of the dependent claim(s).

A method for producing a stator for an electric machine according to the invention comprises a first step a). According to step a), a stator is provided which comprises an annular stator body from which in turn multiple stator teeth arranged spaced from one another in a circumferential direction for receiving stator windings protrude radially to the inside. Between two stator teeth adjacent in the circumferential direction, an intermediate space, the so-called stator slot, is formed in each case.

According to a further step b), at least two stator teeth that are adjacent in the circumferential direction are at least partially overmoulded with a first plastic mass. In this way it is additionally ensured that the stator windings still to be wound onto the stator teeth are electrically insulated relative to the electrically conductive stator teeth after the winding operation.

For this reason, the circumferential sides of the stator tooth facing the intermediate spaces are preferentially overmoulded.

According to a further step c), at least one stator winding is arranged on at least one stator tooth. This operation corresponds to the winding of the stator windings onto the stator teeth. The stator windings can be realised as concentrated or distributed stator windings. According to a further step d), this at least one stator winding is fixed, i.e. permanently fastened to the stator tooth through at least partial overmoulding of this stator winding with a second plastic mass.

According to the invention, a first mask is introduced into at least one intermediate space between the two stator teeth prior to the fixing of the at least one stator winding according to step d), preferentially prior to the overmoulding with the first plastic mass according to step b). This mask covers a surface portion of the stator body bounding the intermediate space radially outside, so that the same during the overmoulding according to step d) is not covered with the second plastic mass, preferentially not with the first plastic mass either. Thus, the region filled out by the first mask forms a hollow space which following the removing of the mask can be flowed through as coolant passage by a coolant.

The cooling of the stator windings can thus take place with a stator produced by means of the method introduced here through the transport of waste heat generated in the stator windings, in particular in the axial end portions of these through the first, second and/or third plastic mass to the coolant passages formed in the stator body. There, the waste heat is absorbed by the coolant flowing through the coolant passages.

Preferably, the procedure described above is applied to multiple of the stator teeth and to multiple of the stator windings. Particularly preferably, the procedure described above is applied to all stator teeth that are present in the stator body and to all stator windings arranged on the stator teeth.

According to a preferred embodiment, the first mask is introduced into a radially outer end portion of the intermediate space concerned.

Following the introducing into the radially outer end portion of the intermediate space, the first mask particularly preferably completely fills out the radially outer end portion.

According to an advantageous further development, the method comprises an additional method step e), according to which the first mask, following the overmoulding with the second plastic mass, is again removed from the intermediate space, so that a hollow space formed following the removing of the first mask forms a coolant passage for a coolant to flow through.

According to a further preferred embodiment, the method comprises an additional method step f). According to step f), the second plastic mass bounding one of the hollow spaces or one of the coolant passages and—alternatively or additionally, the stator winding fixed on the stator tooth by means of the second plastic mass and—alternatively or additionally—a surface portion of the stator body covered by the (first) mask prior to the removal of the same is overmoulded with a third plastic mass. This is preferably carried out in such a manner that the hollow space or coolant passage is fluidically insulated, i.e. separated from the adjacent intermediate space not later than after the overmoulding with the first plastic mass. In this way, any stator windings, protruding out of the second plastic mass are insulated from the coolant flowing through the coolant passage. Preferably, this procedure can be applied to multiple of the existing hollow spaces or coolant passages. Particularly preferably, this procedure can be applied to all of the existing hollow spaces or coolant passages.

Following the carrying out of step f), the coolant passage concerned is thus preferably exclusively bounded by the third plastic mass. An impermissible electrical/mechanical contact of the stator windings with the coolant is excluded in this way.

Particularly preferably, the overmoulding with the third plastic mass is carried out in such a manner that following the overmoulding the hollow space or coolant passage is no longer bounded at any point directly by a stator winding and/or by the stator body. An impermissible electrical/mechanical contact of the stator winding with the coolant is excluded in this way.

Practically, the overmoulding with the third plastic mass is carried out after the removing of the first mask. Thus it is ensured that the surface portions of the stator body covered by the first mask are not covered with the third plastic mass.

According to a preferred embodiment, at least two stator teeth of the stator body provided in step a) that are adjacent in circumferential direction each comprise at an end portion facing away from the stator body at least one extension protruding in the circumferential direction. In this embodiment, the two extensions of the stator teeth that are adjacent in the circumferential direction are situated opposite one another in the circumferential direction. In this way, the two extensions, forming a passage slot, partially bound the intermediate space formed between the stator teeth radially inside. Prior to the overmoulding with the first plastic mass according to step b), a second mask is introduced in an additional method step c′) into the passage slot and, alternatively or additionally, into a region of the intermediate space following the passage slot of the radially inner end portion radially outside. This second mask covers a surface portion of the stator body bounding the intermediate space radially inside, so that the same during the overmoulding according to step d) is not covered by the second plastic mass, preferentially not by the first plastic mass either. Thus, the region filled out by the second mask forms a hollow space out of which later on a coolant passage can be formed. Preferably, the procedure described above is applied to multiple of the stator teeth and to multiple of the stator windings. Particularly preferably, the procedure described above is applied to all of the stator teeth existing in the stator body and to all stator windings arranged on the stator teeth.

According to a further preferred embodiment, the method can comprise a further additional method step e1). According to this step e1), the second mask, following the overmoulding with the second plastic mass, is removed from the passage slot. In this way, a hollow space is created out of which a coolant passage for a coolant to flow through can be created.

According to a further advantageous further development, the method can comprise a further additional method step f1). According to the additional method step f1), the second plastic mass bounding the additional coolant passage and—alternatively or additionally—the stator winding fixed to the stator tooth by means of the second plastic mass and—alternatively or additionally—the surface portion of the stator teeth covered by the (second) mask prior to the removing of the same, is overmoulded with a third plastic mass. This is carried out in such a manner that an additional coolant passage is formed which, following the overmoulding with the third plastic mass at the latest, is fluidically separated from the adjacent intermediate space. In this way, any stator windings protruding out of the second plastic mass are insulated from the coolant flowing through the coolant passage.

Particularly preferably, the additional coolant passage is exclusively bounded by the third plastic mass. An impermissible electrical contact of the stator windings with the coolant is excluded in this way.

Practically, the overmoulding with the third plastic mass is carried out in such a manner that following the overmoulding, the hollow space or coolant passage is not directly bounded by the stator winding and/or by the stator body at any point. An impermissible electrical contact of the stator windings with the coolant is excluded in this way.

Preferentially, the second mask is designed in such a manner that it not only fills out the passage slot formed between the two stator teeth that are adjacent in the circumferential direction, but additionally protrudes radially to the outside into the remaining intermediate space between the two stator teeth. The second mask in this version additionally fills out a radially inner end portion of the intermediate space following the passage slot.

Practically, the second mask, in a cross section of the stator perpendicularly to its centre longitudinal axis, comprises a T-like geometry with a vertical and a horizontal portion. Here, the vertical portion fills out the passage slot whereas the horizontal portion fills out the radially inner end portion of the intermediate space.

The first and/or second mask prove to be particularly producible and thus cost-effective when the same by an insert preferentially formed plate-like or platelet-like, preferentially of steel.

According to an advantageous further development, the method can comprise a further following, additional method step g), according to which at least one outer circumferential side of the body can be overmoulded with a fourth plastic mass.

According to an advantageous further development, axially extending extensions provided on the outer circumferential side of the stator body are also overmoulded with the fourth plastic mass during the overmoulding according to step g), from which axially on the end side, threaded rods for fastening a receptive bearing shield to the stator body, protrude in each case.

The thermal conductivity of both thermosetting plastic and also thermoplastic is adjustable by the choice of the material composition. Thus, the thermal conductivity of a thermoplastic can be equal or greater than that of a thermosetting plastic and vice versa. Usage of thermoplastics has various advantages compared with the use of thermosetting plastics. For example, thermoplastics, as a consequence of the reversible shaping process applied during its processing are better recyclable or compared with thermosetting plastics, are less brittle and have improved damping properties. Since thermoplastics however are usually more expensive in procurement than thermosetting plastics, thermoplastics have to be employed selectively.

According to a preferred embodiment, the first and/or the second and/or the third and/or the fourth plastic mass comprises a thermoplastic or is a thermoplastic in order to exploit the abovementioned advantages.

A further preferred embodiment provides that the first and/or the second/and/or the third and/or the fourth plastic mass comprises a thermosetting plastic or is a thermosetting plastic, by way of which the cost advantages mentioned above can be exploited.

According to a further preferred embodiment, the plastic material of the first, second and/or third plastic mass therefore comprises a thermosetting plastic or is a thermosetting plastic. In contrast with this, the plastic material of the fourth plastic mass in this embodiment comprises a thermoplastic or is a thermoplastic.

According to an advantageous further development, the heat conductivity of the fourth plastic mass is lower than the heat conductivity of the first, second and/or third plastic mass.

According to an advantageous further development, the first, second and third plastic mass has the same thermal conductivity. Alternatively to this, the first, second and/or third plastic mass can each have different thermal conductivities.

According to a further advantageous further development, a coolant resistance of the third plastic mass is greater than the coolant resistance of the second or first plastic mass.

According to a further advantageous further development, the heat conductivity of the first and of the second plastic mass is higher than the heat conductivity of the third and of the fourth plastic mass.

According to another preferred embodiment, two bearing shields, located axially opposite, are fastened, in an additional method step, to the stator body, by means of the overmoulded threaded rods. This is carried out in such a manner that a first bearing shield seals a first hollow space provided in the third and/or fourth plastic mass, which forms a coolant distribution space and for this purpose fluidically communicates with the existing cooling passages. The fastening is additionally performed in such a manner that a second bearing shield seals a second hollow space provided in the third and/or fourth plastic mass, which forms a coolant collection space and for this purpose fluidically communicates with the existing cooling passages. The two bearing shields can be formed in the manner of end plates which are located opposite one another in the axial direction and axially extend the stator body. In one or in both bearing shields, a recess can be provided which expand the respective hollow space provided in the third and fourth plastic mass.

According to a further preferred embodiment, the method comprises two additional method steps h1, h2. According to the additional method step h1, a coolant distribution space and a coolant collection space are provided on and/or in the stator, which via the at least one coolant passage and/or the at least one additional coolant passage fluidically communicate with one another. The coolant distribution space serves for distributing the coolant over the cooling passages, the coolant collection space for collecting the coolant following the flow through the cooling passages. The coolant distributor and the coolant collection space can be arranged in the axial extension of the stator body and lie opposite one another along the axial direction. The coolant distribution space and the coolant collection space can be arranged or formed at least partially in the second plastic mass. Although the electrically conductive stator windings are usually surrounded with an electrical insulation even during their production in order to prevent that upon contact individual winding portions with one another, electrical short circuits are created. However it cannot be ensured that following the manufacture and assembly of the stator windings, all these windings are continuously equipped with such an insulation. According to the additional method step h2, the second plastic mass bounding the coolant distribution space and/or the coolant collection space and/or the axial end portions of at least one stator winding, preferentially all stator windings present in the stator, are therefore overmoulded and/or sprayed with an electrically insulating insulation material. Preferably, an electrically insulating varnish is used for this purpose. Alternatively or additionally, a plastic mass, in particular the third plastic mass and/or the fourth plastic mass, can also be used. In this way, an undesirable electrical short circuit of the coolant present in the coolant distribution space or in the coolant collection space with the electrically conductive stator windings can be prevented.

Particularly, the overmoulding or spraying according to step h2) is carried out in such a manner that following the overmoulding or spraying neither the second plastic mass nor the axial end portions of the at least one stator winding, preferentially of all stator windings, directly bound the coolant distribution space or the coolant collection space. In this way, an undesirable electrical connection of the electrically conductive stator windings with the coolant present in the coolant distribution space or coolant collection space is excluded.

Particularly preferably, the axial end portions of the at least one stator winding are fixed on the at least one stator tooth in step d) of the method or offset in time thereto, i.e. prior to carrying out step d) or after carrying out step d), by means of a plastic mass, preferentially by means of the second plastic mass.

The invention, furthermore, relates to a stator that has been produced by means of the method explained above. The advantages of the method according to the invention explained above therefore apply also to the stator according to the invention.

The invention, furthermore, relates to an electric machine having the stator mentioned above, which consequently is produced by means of the method according to the invention. The advantages of the method according to the invention explained above therefore apply also to the electric machine according to the invention. Besides the stator, the electric machine also comprises a rotor which is rotatable about an axis of rotation relative to the stator.

Further important features and advantages of the invention are obtained from the subclaims, from the drawings and from the associated figure description by way of the drawings.

It is to be understood that the features mentioned above and still to be explained in the following cannot only be used in the respective combination stated but also in other combinations or by themselves without leaving the scope of the present invention.

Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description.

