BACKGROUND OF THE INVENTION

The invention relates to a stator for an electric machine and a method for producing a stator. The invention in particular relates to an electric machine having a stator and a rotor.

From the state of the art, stators for electric machines such as, for instance, electric motors or electric generators are known, see application document US2010/0192357, for example.

Stators may be built up, for example, from a laminated stator sheet package with a substantially circular ring, the so-called yoke, from which webs, which form teeth, are directed inward. Between these teeth are free spaces, so-called grooves, into which the stator windings are introduced.

In stators according to the state of the art, the windings often must be laid around the teeth from the inside between the lateral ends of the teeth tips. On the one hand, this is quite complex, on the other hand it is difficult to achieve a high degree of filling in the winding spaces (grooves), which might require a larger structural form of the motors. This may furthermore also entail higher costs of a motor.

Moreover, the magnetic flux between the yoke ring and teeth is possibly not optimal in stators according to the state of the art so that the performance of an electric machine having such a stator may be restricted.

SUMMARY OF THE INVENTION

It is a task of the invention to solve the problems of the state of the art at least in part. In particular, it is a task of the invention to provide an improved stator. It is furthermore a task of the invention to provide a stator having increased torque, in particular having increased continuous torque. Furthermore, it is a task of the invention to provide a stator by means of which an improved and/or cost-efficient tooth winding process may be performed.

The task is solved by a stator as disclosed herein, an electric machine having a stator as disclosed herein, and a method for producing a stator as disclosed herein. Advantageous further developments and embodiments will result from the dependent claims and from this specification.

One aspect of the invention relates to a stator for an electric machine having a yoke ring, a plurality of teeth arranged side by side within the yoke ring in the circumferential direction, wherein each tooth has a yoke portion, wherein the yoke portions of the teeth support one another in the circumferential direction, wherein at least a part of the outer circumference of the yoke portion of each tooth deviates from a circle segment shape that is concentric to the central axis of the stator, and the outer circumference encloses at each point an angle of more than 45° with the radius defined by the central axis.

A further aspect relates to an electric machine having a stator in one of the typical embodiments described herein, and a rotor arranged within the stator and being concentric to the stator.

A further aspect relates to a method for producing a stator in one of the typical embodiments described herein for an electric machine. Typically, the production method comprises: arranging a plurality of teeth side by side along a circumferential direction, wherein each tooth has a yoke portion; joining a yoke ring to the arranged plurality of teeth so that the yoke portions of the teeth support one another in the circumferential direction, wherein the yoke ring is made of a ferromagnetic material permeated by an electric insulator for suppressing eddy currents. Typically, the yoke ring is punched as a compound die. A part of the outer circumference of the yoke portion of a tooth typically is a straight or curved portion of the outer circumference of a tooth.

Typically, by the term “outer circumference” that part of the yoke portion is designated which delimits the tooth towards radially outside, or that part which is adjacent to the yoke ring. In typical embodiments, these definitions designate the identical part of the tooth yoke portion.

Typically, the angle arises as a cutting angle between the tangent to the outer circumference at one point, and by a straight line generated by the radius through the central axis of the stator.

Typically, the angle enclosed by the outer circumference at one point and the radius through the central axis of the stator designates the smaller of the two angles. As far as angles are considered herein, “radius” typically designates a straight line which, for the angle determination, reaches beyond the outer circumference. Typically, the angle is defined by the outer circumference at one point and the radius through that point. Typically, the angle is related to the angle enclosed by the tangent of the outer circumference at this point and the radius at this point. Typically, the angle at each point of the outer circumference of the yoke portion of the tooth is at least 45°, at least 50°, at least 55° or at least 60° or a maximum of 90°. An advantage of such flat angles may be that the occurrence of undesired or unplanned constraining forces is avoided, or undesired or unplanned constraining forces are at least reduced. Such flat angles may also assist in avoiding or reducing mechanical repetition. The mentioned angle of at least 45° may be considered identical to the following definition: the tangent of the outer circumference runs at least as much in the circumferential direction as in the radial direction, typically more in the circumferential direction than in the radial direction.

In the present disclosure, the yoke portions of the teeth support one another in the circumferential direction. In embodiments of the present disclosure, the yoke portions of the teeth can support one another directly. For example, when being directly supported, the yoke portion of a tooth is in direct contact with an adjacent yoke portion of a respectively adjacent tooth. The boundary surface between two teeth may in this case be planar, in particular a plane oriented in the radial direction, or be realized to be deviating from a plane, for example in the form of a tongue-and-groove arrangement or having a wedge shape.

According to the present disclosure, the yoke ring is made of a ferromagnetic material. For suppressing eddy currents, the ferromagnetic material of the yoke ring is typically permeated by an electric insulator. The yoke ring may be composed, for example, at least to 90% of a ferromagnetic material permeated by insulating material. According to one embodiment, the yoke ring can have a material interrupted by an insulating material.

According to embodiments described herein, the yoke ring may be pressed or shrunk onto the entirety of the teeth. The plurality of the teeth is thereby compressed radially to the inside by the yoke ring. Due to the arrangement of the yoke portions described herein, the teeth support one another in the circumferential direction. The arrangement of the yoke portions can be understood illustratively as a self-supporting arch of a building, for example, a round arch.

In further embodiments, adjacent yoke portions may support one another at least indirectly. An indirect support of the yoke portions may be realized as a connecting element, for example, which connects one yoke portion, in particular all of the yoke portions, to a respectively adjacent yoke portion.

In embodiments of the present disclosure, the ferromagnetic material of the yoke ring may be an SMC. In this case, SMC designates a material of a so-called “Soft Magnetic Composite”. SMC typically may be a material of soft magnetic composite materials of powder, wherein single particles of the material have an electrically insulating coating. The material of the SMC may comprise iron or iron alloy, for example. The material of the SMC may have an iron content of about 70% or more, about 75% or more, about 80% or more, or about 85% or more, for example. In further embodiments, the plurality of teeth may be made of an SMC.

In preferred embodiments, the yoke ring is made of a laminated material or of a laminated sheet package. In further preferred embodiments, also the plurality of teeth may be made of a laminated material or of a laminated sheet package. Laminated sheet package or laminated realization means a realization in which partial laminated sheet packages are composed of single thin sheets of metal, which can also be called lamellae. Here, a component manufactured from single sheets of metal is understood as a partial laminated sheet package, wherein the component is a subcomponent of the stator. The single lamellae of a partial laminated sheet package usually lie axially on top of each other and are typically electrically insulated from each other by a thin insulation layer so as to suppress eddy currents within the laminated sheet package.

A laminated sheet package, for example, may be built up of a plurality of single laminated sheet packages or a plurality of single sheets of metal. The yoke ring, for example, may be manufactured from a plurality of one-piece metal sheet rings. The sheet thickness of the single lamella typically is about 0.1 mm to about 1 mm. When the stator, for example, has an axial laminated sheet package length of 40 mm, each partial package, depending on the sheet metal thickness, is typically composed of 400 to 40 single lamellae. In embodiments, the laminated sheet package outer diameter of the yoke ring may be 100 mm to 200 mm, for example. The laminated sheet package is typically inherently form-fit and force-fit.

As a joining technique between the single lamellae of the partial laminated sheet packages, the Backlack technique may be used, for example, in which adjacent single lamellae are glued together substantially over the complete surface. In general, other joining techniques are also conceivable, e.g. punch-packing or welding. The Backlack technique may in particular have the advantage that the joining process of the partial packages is assisted since each partial package itself can have high rigidity and at the same time high shape accuracy.

According to embodiments described herein, the winding upon the respective teeth from the plurality of teeth may be performed by a coil extending around the respective tooth prior to joining by the yoke ring. Thereby, a partial or complete automation of the winding process may be achieved. In particular, a direct winding upon the teeth may thereby be enabled.

The term “direct winding” herein describes a winding in which the winding wire is directly wound around the tooth. In case of a non-direct winding, for example, the coil is first wound on a device and shifted upon the tooth after the winding on the device is completed.

A direct winding may further result in a higher copper filling factor, whereby the continuous torque of the electric machine can be increased. In embodiments, the continuous torque may be increased by at least 30%, for example.

In typical embodiments, the method may comprise at least one of pressing or shrinking the yoke ring upon the plurality of the arranged teeth, casting and/or impregnating.

According to embodiments described herein, each tooth has a radially inner tooth tip. Typically, adjacent tooth tips do not touch one another. The tooth tips may in particular be separated by groove slots or so-called tooth tip gaps.

In typical embodiments, the outer circumference of at least a part of the yoke portions of the teeth is deviating from a circle segment shape that is concentric to the central axis of the stator. In particular, the outer circumference or a part of the outer circumference of at least one tooth may deviate such that the at least one tooth is centered in the yoke ring in the circumferential direction. In embodiments, the outer circumference of each tooth of the stator may deviate from a circle segment shape. In typical embodiments, all of the teeth or at least 90% of the teeth are formed to be identical or at least substantially identical. Typically, the geometry of the yoke portions and the yoke ring are selected, for example, in an embodiment having partial laminated sheet packages, such that a favorable distribution of the mechanical tensions may be achieved in the entire laminated sheet package. An elliptical deformation of the stator or the yoke ring can be avoided.

According to embodiments described herein, at least a part, in particular a substantial part of the yoke portions may have an in particular outward directed wedge shape in cross section. In embodiments, a wedge shape having an obtuse angle of larger than 90° and smaller than 180° or smaller than 150° is possible. The cross section here refers to a cross-sectional plane perpendicular to the central axis of the stator. In embodiments, all of the yoke portions may have an in particular outward directed wedge shape. In embodiments, at least a part of the yoke portions may have at least a radially inward directed wedge shape, or in addition or instead a radially outward directed wedge shape in cross section.

Typically, the yoke portions of the teeth have a continuous increase of the radial cross section from the outer edges of the yoke portions to the centers of the yoke portions in the circumferential direction. At the outer edges, the yoke portions, in particular of different or adjacent teeth, abut directly or indirectly in typical embodiments. In this manner, the yoke portion may have an outward directed wedge shape, for example, also with a kink of the outer circumference on both sides of the center. Typical yoke portions or typical teeth are constructed to be symmetrical to a radially oriented center line. Typical yoke portions have an outer circumference which is formed to be symmetrical to a radially oriented center line of the tooth or the yoke portion.

In embodiments of the present disclosure, a form closure is present in the circumferential direction in particular between at least a part of the teeth, in particular the respective yoke portions of the teeth, and the yoke ring.

In typical embodiments, the yoke ring can be shrunk or pressed upon the teeth. This allows a close form closure between the yoke ring and the teeth or between the yoke ring and the respective yoke portions of the teeth to be achieved. The magnetic flux guidance may thus be improved.

In embodiments, the inner side of the yoke ring may deviate from a circular shape. In embodiments having outward directed wedge shapes of the yoke portions, the inner side of the yoke ring may have a recess that is complementary to the wedge shape. This allows the accuracy of the position of the teeth to be improved in the circumferential direction. Typically, the inner side of the yoke ring in the portion of a tooth has a shape that is complementary to the outer circumference of the yoke portion of the tooth.

The outer circumferences of typical exemplary embodiments may serve the purpose of circumferentially centering each tooth in the yoke ring. This allows the torque transmission between teeth and yoke ring caused by the form closure to be secured or improved even in case of low surface pressure. Due to typical outer circumferences of the yoke portions of the teeth, the yoke ring generates normal forces obliquely relative to a radial direction, while the yoke ring itself may have a high width and stability between the teeth, i.e. in the angle area of the grooves situated between the teeth.

In embodiments of the present disclosure, each tooth typically has a coil extending around the respective tooth, such as a copper coil, for example.

Typically, in the radial cross section, the yoke ring at the edges of the outer circumference of each tooth, is at least 1.3 times, at least 1.5 times, more than 1.5 times, at least 2.5 times or at least 3.5 times or at maximum 5 times or at maximum 3.5 times as thick in the radial direction as the yoke portion of the tooth at the same point in the circumferential direction. In typical embodiments, the yoke ring is in the radial cross section in the center of the respective outer circumference of each tooth at least 0.5 times or at least 0.7 times or at most 1.5 times or at most 1.3 times as thick as the yoke portion at the same point in the circumferential direction.

These dimensions each are advantageous for the shape accuracy of the stator, in particular when the yoke ring and the teeth are laminated. Moreover, high magnetic flux guidance can be achieved, during which magnetic asymmetries are avoided.

In embodiments, the radial extension of the yoke ring and yoke portions at the edge of a yoke portion may have a ratio of at maximum 6:1 and/or at minimum 2:3. For example, at the joint between two adjacent teeth or yoke portions, a ratio of the yoke ring to yoke portions may be at maximum 4:1 and/or at minimum 3:2. This allows high magnetic flux guidance to be achieved.

Typically, the outer circumference of the yoke portion of a tooth respectively comprises at least two straight portions. Typical embodiments having straight portions may be punched at higher process safety than having curved portions.

Typically, the outer circumference of the yoke portion of a tooth is respectively made up from not more than ten straight portions or comprises not more than ten straight portions. In addition to the straight portions, at least one or exactly one curved, in particular outward curved portion, also referred to as a fillet, may further be present in embodiments, or exclusively straight portions may be present in embodiments.

In typical embodiments, a fillet is provided at the wedge shape or between respectively the middle sections of an outer circumference of a tooth. Typically, the fillet points radially outward, and thus is curved to the outside as seen from the tooth. Typically, between the straight portions joining the fillet and the fillet there is no kink. In further embodiments, a kink is provided at the transition from the straight portion to the fillet.

In typical stators of exemplary embodiments, the outer circumference of the yoke portion of a tooth comprises respectively at least or exactly four straight portions.

At the respective center of the outermost portions, the outer circumference typically encloses respectively an angle of at least 70°, more than 75°, more than 80°, or more than 83°, and at most 85°, and/or less than 90° with the radius defined by the central axis. The outermost portions are respectively the straight portions starting at the edges on both sides of the yoke portion. The center of a portion respectively designates the center of the straight line of this straight portion. The angle, if possible, is the smaller angle enclosed by the straight line of the straight portion, and the radius running through the central axis and the center of the portion. The central straight portions are the portions each lying closest to the center of the outer circumference of the yoke portion of a tooth and are each adjacent to a centrally arranged fillet or abutting directly in the center. Typically, the outermost straight portions are only slightly inclined or less inclined than the central portion relative to the circumferential direction. In this way, a stabilization of the position of the tooth in the yoke ring may be achievable.

At the respective center of the central portions, the outer circumference typically encloses respectively an angle of at least 45°, at least 55°, at least 60°, or at most 75° with the radius defined by the central axis. Hence, the central portions are typically steeper relative to the circumferential direction than the outer portions. In case of more than two portions on both sides of the center, the slope of the straight portions with respect to the circumferential direction typically increases toward the center.

Advantages of typical embodiments may comprise: more material at the yoke ring, in particular in embodiments having four straight portions of the outer circumference, a statically determined accommodation of the teeth in the yoke ring, a greater length of the outer circumference so that the magnetic flux can be improved, as well as mutual interlocking of the yoke ring and the yoke portions.

