Motor stator for an electric motor and method for manufacturing the motor stator

The invention is related to a method for manufacturing a motor stator for an electric motor and to an associated motor stator for an electric motor.

Motor stators are used for electromagnetically driving the rotor of an electric motor, for example in an automotive electric coolant pump. The motor stator is provided with a number of stator teeth, each stator tooth being wound with an electroconductive wire to provide a plurality of electromagnetic stator coils.

The efficiency of the electric motor is generally depending on the fill factor of the stator coil winding. The higher the fill factor of the winding is, the better is the efficiency of the electric motor. With an orthocyclic winding the fill factor of a coil wire with a circular cross-section can be up to 90% resulting in a relatively high efficiency of the electric motor.

An orthocyclic automatic winding of conventional stator bodies is complicated and expensive. Because of the circular arrangement of the stator teeth, the adjacent stator teeth restrict the lateral accessibility of each stator tooth. As a result, the clearance between the adjacent stator teeth is not sufficient to allow an orthocyclic winding. For example, an inner-grooved stator cannot be wound orthocyclically, as it can only be wound by a needle winder.

For that reason, new stator designs have been provided to allow an orthocyclic winding of the stator teeth and to even allow the orthocyclic winding of inner-grooved stators being connected by a back-iron ring. EP 0 969 581 A2 discloses a stator body being assembled from several stator segments. These stator segments are wound with an electroconductive coil wire before assembling the stator body, so that the lateral accessibility of the stator teeth for an orthocyclic winding is ensured. The stator segments are connected by a detachable hinge, so that a circular ring-shaped stator body with inner grooves is formed.

EP 1 748 531 Al discloses a circular stator body, which is made of a substantially linear metal strip with a chainlike arrangement of the stator teeth being connected by film hinges. The metal strip is deformed to improve the accessibility of the stator teeth for the winding process. After being wound, the metal strip is re-deformed into a circular ring-shaped and inner-grooved stator body with the stator teeth being connected by a back- iron ring.

DE 10 2010 026 527 Al discloses a method for winding the coils of a stator with a pole-star stator body. The stator teeth are not wound directly, but are provided with detachable coil bodies being wound before attaching them to the pole-star.

All of these stator body designs allow an orthocyclic winding of the stator coils, but the segmented stator body or the stator with detachable coil bodies require an additional assembly step. Due to the deformation of the film hinges of the stator body made of the chainlike structure, the film hinges, which define the back-iron ring are plastically deformed, so that the magnetic permeability of the back-iron ring is reduced. Further, the diversity of the (electromagnetic) air gaps between the pole teeth additionally reduces and dehomogenizes the magnetic flux of the back-iron ring. It is an object of the invention to provide a cost-efficient motor stator for a high efficiency electric motor and a method for manufacturing the motor stator.

This object is achieved by a manufacturing method of a motor stator with the features of claim 1 and with a motor stator of one of the claims 5-9.

A manufacturing method of a motor stator for an electric motor according to the invention comprises the following manufacturing steps, wherein the motor stator is provided with a closed ring-shaped stator body, which comprises a plurality of stator teeth being connected by connection bridges with the two adjacent stator teeth:

In a first manufacturing step according to the invention, the closed circular ring-shaped stator body is mechanically deformed at the connection bridges connecting the adjacent stator teeth. The stator tooth, which is to be wound, is exposed by laterally folding away its adjacent stator teeth. The adjacent stator teeth are folded away such that the exposed stator tooth is laterally accessible by a winding machine, which allows an orthocyclic winding, for example by a flyer winding machine or a linear winding machine.

In a second manufacturing step according to the invention, an electroconductive coil wire is wound around the exposed stator tooth. Due to the improved lateral accessibility, the exposed stator tooth can be wound orthocyclically and substantially perpendicularly to the stator tooth centreline, for example by a flyer winding machine. This results in a relatively high fill factor of the winding.

In a third manufacturing step according to the invention, the first and second manufacturing step are repeated for every remaining stator tooth of the stator body. Accordingly, the stator body is again deformed for exposing every single stator tooth.

In the fourth manufacturing step according to the invention, after all stator teeth have been provided with a coil, the stator body is mechanically redeformed back into a circular ring-shape. The re-deformation of the stator body into a circular ring-shape is achieved, for example, by attaching the deformed stator body to a conical mandrel.

Preferably, two stator teeth of the stator body, which are opposite to each other are exposed pairwise and antiparallel. For example, the stator body can be deformed into an oval ring-shape. The two opposite and antiparallel stator teeth are arranged centrically to the longitudinal axis of the oval ring, so that the centrelines of the opposite stator teeth are co-linear and substantially co-axial with the longitudinal axis of the oval ring-shaped stator body. The number of the deformation steps of the stator body is thereby reduced by 50%, because with one deformation step two opposite stator teeth are simultaneously exposed and prepared for the orthocyclic winding process step. This reduces the total manufacturing time of the stator body.

Preferably, the pairwise exposed stator teeth are wound one after another. For this sequentially winding of the exposed stator teeth, only one winding machine is required. After winding the first exposed stator tooth, the stator body is, for example, rotated by 180°, so that the second antiparallel exposed stator tooth can be wound immediately afterwards.

More preferably, the pairwise exposed stator teeth are wound simultaneously. A simultaneous winding of two opposing stator teeth requires a winding machine with two machine heads or two separate winding machines, but additionally reduces the winding process time of the stator teeth by another 50%.

In a motor stator for an electric motor manufactured by a method according to the invention, the connection bridges between the adjacent stator teeth preferably have been plastically deformed. This plastic deformation results from the deformation process step during the manufacturing of the motor stator to expose the stator teeth for an orthocyclic winding of the stator coils. The plastic deformation of the connection bridges results in a distortion of the crystalline grid structure of the connection bridges material, so that the reluctance in the connection bridges is increased. The increased reluctance and the resulting decrease of the magnetic permeability of the plastically deformed connection bridges reduce the iron losses resulting from the magnetic short circuit over the connection bridges between the adjacent pole shoes. The magnetic permeability is thereby reduced by at least 50%.

Preferably, the stator body is made of a stack of metal sheets. The metal sheets are, for example, punched out of large sheet metal coils with an electrical insulation coating. The identical metal sheets are stacked together and are mechanically connected to a solid stator body, for example, by an adhesively bonding connection or by a form-locked connection like punch-packing.

Preferably, the motor stator defines a circular central rotor opening. The motor stator is thereby preferably used in an electric motor with an inner motor rotor rotating within the central rotor opening. The circular central rotor opening defines a constant circular ring gap between the motor stator and the circular motor rotor. Preferably, the stator body is defined by an outer-grooved pole star. Accordingly, the stator teeth are not directly connected over the outer circumference of the stator body. As a result, the stator coils can be wound from the outside, so that winding methods are applicable, which allow an orthocyclic winding of the stator coils, for example flyer winding or linear winding.

Preferably, the stator body is not provided with an integral back-iron ring. Accordingly, the back-iron ring is a separate component, which is assembled after completely winding all stator coils. The mechanical connection between the adjacent stator teeth is preferably provided by connection bridges between the pole shoes of the stator body.

An embodiment of the invention is described with reference to the enclosed drawings, wherein figure 1 shows an embodiment of the motor stator in a not deformed state in a top view, figure 2 shows the motor stator of figure 1 in a deformed state with two exposed stator teeth in a top view, and figure 3 shows the motor stator of figure 1 in a cross-sectional view.

Figure 1 shows an embodiment of the motor stator 10 with a substantially circular star-shaped ferromagnetic stator body. The outer-grooved stator body 15 comprises six radially oriented and equiangularly arranged stator teeth 20. Each stator tooth 20 comprises a substantially arc-shaped pole shoe 22 with an inner plane coil flange 23, a cuboid-shaped winding section 25 extending radially outwards from the pole shoe 22 to an arc-shaped stator tooth tip 27 with a stator tooth flange 28. The stator teeth 20 are connected to each other by a strut-type and arc-shaped connection bridge 30, so that the arc-shaped pole shoes 22 and the arc-shaped connection bridges 30 define a circular central rotor opening 18.

Figure 2 shows the motor stator 10' with a deformed stator body 15' of figure 1. The stator body 15' is deformed into an oval closed ring-shape by deforming all connection bridges 30 between the stator teeth 20. The two longitudinal oriented stator teeth 20A, 20B are exposed pairwise by laterally folding away the adjacent stator teeth 20C, 20D, 20E, 20F so that the exposed stator teeth 20A, 20B are oriented antiparallel and are oriented perpendicularly to the other non-exposed stator teeth 20C, 20D, 20E, 20F. Thereby the connection bridges 30' of the exposed stator teeth 20A, 20B are deformed by up to 30° each, because the angle between the stator teeth 20A and 20C, between 20A and 20F, between 20B and 20D or between 20B and 20E changes from 60° to 90°. As a result, the centreline Cl of the stator tooth 20A and the centreline C2 of the stator tooth 20B are co-linear and are coaxial to the longitudinal axis L of the oval ringshaped stator body 15'. The remaining connection bridges 30" between the stator teeth 20D and 20F and between 20C and 20E are deformed even more by up to 60°, as they are oriented parallel to each other after the stator teeth 20A and 20B have been exposed. In addition, the connection bridges 30" connecting the non-exposed stator teeth 20C, 20D, 20E, 20F are deformed in opposite folding direction compared to the folding direction of the other connection bridges 30'. After all stator teeth 20A, 20B, 20C, 20D, 20E, 20F have been wound, all connection bridges 30', 30" have been deformed by 30° in a first direction and by 60° in the second opposite direction referred to the original star-shaped arrangement of the stator teeth 20 of figure 1. As a result, the total deformation angle of each connection bridge 30', 30" is nearly 90°. Due to the exposing of the stator tooth 20A, the winding section 25 of the stator tooth 20A is laterally accessible, so that the winding space W, which is circumferentially surrounding the winding section 25, is not restricted by the adjacent stator teeth 20. As a result, the stator tooth 20A can be wound orthocyclically with an electroconductive coil wire 50, for example, by a flyer winding machine 55. The resulting stator coil 52 extends between the stator tooth flange 28 and the coil flange 23 over the complete winding section 25. After the stator tooth 20A has been wound, the oval stator body 15' is rotated by 180° in the cross plane for winding the second exposed opposite stator tooth 20B. After winding the second stator tooth 20B, the stator body 15' is deformed in the same manner to expose the next pair of stator teeth 20C, 20D for the winding process. After another deformation step, the remaining pair of stator teeth 20E, 20F is exposed for winding. Finally, after all stator teeth 20A-F have been wound, the stator body 15' is re-deformed into the circular star-shaped motor stator 10, which is shown in figure 1.

Figure 3 shows the stator body 15 of the motor stator 10 of figure 1 in a cross-sectional view. The stator body 15 is made of a stack 40 of mechanically connected identical star-shaped metal sheets 45, which are made of a ferromagnetic material. The single metal sheets 45 are electrically insulated by an insulation coating (not shown).