Patent Publication Number: US-2021175759-A1

Title: Stator for an electric machine and electric machine

Description:
The present application relates to a stator for an electric machine and an electric machine. 
     Typically, electric machines comprise a stator and a rotor that is movable to it. Electric machines may function as a motor type or a generator type, wherein electric energy is converted into kinetic energy or vice versa. During operation, a magnetic field of the rotor interacts with a magnetic field of the stator. 
     In order to operate the electric machine efficiently, an objective is to generate a torque as high as possible. Moreover, losses should be reduced in the electric machine. For this purpose, for example, so-called flow barriers may be provided within the stator. The flow barriers partially extend through the stator and are filled with air. However, even when flow barriers are used, losses may occur due to the harmonic components of the magnetomotive force which are not utilized for generating the torque. 
     One task to be solved is to proposes a stator for an electric machine which can be operated in an efficient manner. A further task to be solved is to propose an electric machine which can be operated in an efficient manner. 
     The tasks are solved by the subject matters of the independent claims. Advantageous configurations and further developments are indicated in the dependent claims. 
     According to at least one embodiment of the stator for an electric machine, the stator comprises slots for receiving electric windings. The stator has a longitudinal axis. The slots may be recessed in the stator. The slots each may extend along the entire longitudinal axis of the stator. The slots may be arranged completely within the stator. In this case, the slots do not have openings to the outside of the stator. It is further possible that the slots each have at least one opening. The openings, for example, may be arranged on an inner side of the stator. For example, the openings may be arranged on a side of the stator, where a rotor of the electric machine may be arranged. The slots may be distributed along the circumference of the stator. For example, the slots may be evenly distributed along the circumference of the stator. 
     The stator furthermore comprises at least two teeth, wherein one tooth of the stator respectively is formed between two adjacent slots. Thus, a tooth and a slot are alternately arranged along the circumference of the stator. Within the slots, electric windings of the stator may be arranged. For this purpose, an electric winding is wound around each tooth of the stator, for example. In this case, the electric windings are arranged within the slots at least in some places. It is further possible for an electric winding to be wound around every second tooth of the stator. In these cases, this is a concentrated winding. Other concentrated winding systems are also possible. The electric windings each have an electrically conductive material. The electric windings may be connected to power electronics and be configured to generate a rotating field. The teeth may be evenly distributed along the circumference of the stator. Furthermore, the teeth each may have the same extension along the circumference of the stator. However, it is also possible for the teeth to be differently sized. 
     At least two of the teeth have a recess extending at least partially through the respective tooth. The recesses each may extend through the stator completely along the longitudinal axis. This means, the recesses each may extend in parallel to the adjacent slots. The stator can have a plurality of laminated sheet packages into which the slots and the recesses are introduced. The laminated sheet packages can have iron. Recess correspondingly means the absence of the material of the laminated sheet packages or the absence of material carrying the magnetic flux, such that the magnetic flux is inhibited in the area of the recess. 
     Within the recesses, two electric conductors each are arranged which are short-circuited to one another. The electric conductors each have an electrically conductive material. For example, the electric conductors each are wires. The electric conductors may extend along the longitudinal axis of the stator completely through the stator. The electric conductors arranged within the same recess are short-circuited to one another. Furthermore, electric conductors arranged within different recesses may likewise be short-circuited to one another. 
     During operation of the electric machine, a voltage is induced in the electric conductors within the recesses. The voltage in the electric conductors, for example, is generated by the fundamental wave of the stator&#39;s magnetic field. Thus, the electric conductors are self-excited by the fundamental wave. The voltage generated in the electric conductors results in a current and thus to an additional magnetic flux. Since the electric conductors are short-circuited to one another, current may flow and a magnetic flux is generated. It has been shown that this additional magnetic flux results in the torque of the electric machine being increased and rotor losses being reduced. Moreover, undesired harmonic components of the magnetomotive force may be reduced significantly. 
     In this case, all harmonic components are deemed as being undesirable which are not utilized as an operating wave. These may be higher harmonics and/or sub-harmonics, wherein the terms higher and sub-, each refer to the order of the harmonics utilized as an operating wave. The reduction of the undesired harmonic, for example the fundamental wave which has the ordinal number of 1 allocated, in turn leads to the efficiency degree of the electric machine being increased or undesired acoustic impairments and vibrations being reduced. 
     The additional magnetic flux generated by the electric conductors may result in the fundamental wave and further sub-harmonics of the magnetomotive force being reduced. At the same time, the harmonic component utilized for generating the torque, which consequently is utilized as the operating wave, may be increased. Thus, the nominal torque of the electric machine may be increased. 
     Furthermore, due to the electric conductors within the recesses, the iron losses and magnetic losses of the electric machine are reduced. Thus, the efficiency degree of the electric machine is higher as a whole. This means, the electric machine can be operated more efficiently. 
     The recess including the electric conductors does not require any significant additional effort during manufacturing, since the stator&#39;s laminated sheet packages usually are punched parts anyway and the recess can be punched out in the same work step. The electric conductors may subsequently be arranged within the slots. 
     According to at least one embodiment, the recesses each extend in a radial direction, wherein the radial directions each run in parallel to a radius in a cross-section through the stator, and the radius runs through the respective tooth. The cross-section through the stator runs perpendicular to the longitudinal axis of the stator. The stator may have approximately the shape of a cylinder. The stator then has the shape of a circle in cross-section. The radial directions each run in parallel to a radius within the circle. The radial directions, in which the recesses respectively extend, each run in parallel to a radius through the respective tooth. This means that a radius running centrically through the tooth is assigned to each tooth. Along the respective radial direction, the recesses may extend partially or completely through the stator. Apart from the electric conductors, air may be arranged within the recesses. Thus, the recesses act as flow barriers within the stator. By arranging the electric conductors within the recesses, the torque generated by the electric machine during operation is increased. Moreover, the electric machine as a whole can be operated more efficiently. 
     According to at least one embodiment, at least every second tooth has a recess. This means that at least every second tooth has one of the recesses along the circumference of the stator. Around the teeth having no recesses, the electric windings of the stator may be wound. Thus, an electric winding is wound around every second tooth. This structure enables an efficient operation of the electric machine. 
     According to at least one embodiment, each tooth has one of the recesses. 
     According to at least one embodiment, at least one of the electric conductors cannot be electrically contacted from outside the stator. This can mean that the electric conductor is completely arranged within the stator. Moreover, the electric conductor is not arranged on an outside of the stator. Thus, the electric conductor is not accessible from outside the stator. An access to the electric conductor from outside the stator is not possible. Consequently, the electric conductor is not connected to power electronics. Thus, the electric conductor within the recesses serves as an electrically conductive material in which a voltage is induced during operation of the electric machine. The induced voltage results in current and an additional magnetic flux. As described above, this enables the electric machine to be operated more efficiently. 
     According to at least one embodiment, the electric conductors respectively do not fill the recess completely. This means that not the entire volume of the recesses is filled with the electric conductors. Apart from the electric conductors, the recesses may be filled with air. Since the electric conductors do not fill the recesses completely, the electric conductors may be placed easily within the recesses. 
     According to at least one embodiment, electric conductors within two recesses are electrically connected together. In the cross-section through the stator, the recesses are distributed along the circumference of the stator. The two recesses are arranged at different positions along the circumference of the stator. The electric conductors within the two recesses each may form a closed ring which partially extends through the two recesses. The ring is arranged completely within the stator, for example, so that it cannot be contacted from outside the stator. Thus, a voltage may be induced in the electric conductors during operation of the electric machine. As explained above, this enables the electric machine to be operated more efficiently. 
     According to at least one embodiment, electric conductors within two recesses are electrically connected together which are opposite to one another in a cross-section through the stator. Two recesses which are opposite to one another in a cross-section through the stator extend in a cross-section through the stator along a straight line. 
     According to at least one embodiment, electric conductors within two further recesses are electrically connected together, wherein the electric conductors within the two recesses are electrically isolated from the electric conductors within the two further recesses. The further recesses may have the same structure as the recesses. Thus, the electric conductors may be arranged within the two further recesses as described for the recesses. 
     Preferably, the stator has four further recesses, in which electric conductors are arranged. In this case, two further recesses respectively are opposite to one another in a cross-section through the stator. Moreover, the two recesses are opposite to one another in a cross-section through the stator. Electric conductors within recesses or further recesses, which are not opposite to one another in a cross-section through the stator, are electrically isolated from one another. Thus, a three-phase voltage develops within the electric conductors, which enables a constant additional torque. Thus, the electric machine as a whole can generate a higher torque during operation. 
     According to at least one embodiment, the electric conductors have a metal. The electric conductors, for example, have copper. Thus, the electric conductors constitute an electrically conductive material in which a voltage may be induced. This enables the electric machine to be operated efficiently. 
     According to at least one embodiment, the recesses each have an additional slot. This may mean that the recesses each are formed as an additional slot. The additional grove may be open towards an inside and/or towards an outside of the stator. It is further possible for the additional slot to be arranged completely within the stator sheet. The electric conductors arranged within the recesses enable the electric machine to be operated efficiently. 
     According to at least one embodiment, the recesses each have an additional slot which extends completely through the stator from an inside to an outside. The inside of the stator may be the side where a rotor of the electric machine may be arranged. In this case, the outside is the side of the stator facing away from the inside. Thus, the recesses extend further through the stator than the slots. The recesses thus act as flow barriers. Moreover, the electric conductors arranged within the recesses enable the electric machine to be operated efficiently. 
     Furthermore, an electric machine is proposed. According to at least one embodiment of the electric machine, the electric machine has a stator. Thus, all of the features of the described stator are also disclosed for the electric machine and vice versa. The electric machine further has a rotor that is movable relative to the stator. The rotor may be an internal rotor or an external rotor. If the rotor is an internal rotor, an outside of the rotor is facing the stator. The rotor may be arranged on a shaft of the electric machine. Between the stator and the rotor, an air gap may be arranged. The rotor may have permanent magnets. The permanent magnets may be arranged at the side of the rotor facing the stator. As described above, the electric machine has an increased efficiency degree and the losses are reduced. Thus, the electric machine may be operated more efficiently. 
     According to at least one embodiment of the electric machine, an operating wave of the magnetomotive force is different from a fundamental wave of the magnetic flux during operation. This means that a harmonic component of the magnetomotive force having an order of higher than 1 is used as the operating wave, for example. For example, the 7 th  harmonic of the magnetomotive force is used as the operating wave. This means that this component of the magnetomotive force is utilized during operation of the electric machine for generating torque. In conjunction with the recesses and the electric conductors within the recesses, the use of a higher harmonic component than the fundamental wave as an operating wave enables the electric machine to be operated efficiently. 
     According to at least one embodiment of the electric machine, the recesses are in connection with an air gap arranged between the rotor and the stator. This means that the recesses are open towards the air gap. Consequently, air is partially present within the recesses. The recesses thus form flow barriers. Furthermore, the recesses may be closed towards a side of the stator facing away from the rotor. This means that the recesses do not extend completely but only partially through the stator in the radial directions. This results in rotor losses being further reduced and thus the efficiency degree being increased. The electric machine may therefore be operated more efficiently. 
     According to at least one embodiment of the electric machine, the recesses are open towards the side of the stator facing away from the rotor. This means that the recesses may be open towards an outside of the stator. In addition, the recesses may be in connection with the air gap. In this case, the recesses extend completely through the stator in the radial directions. However, it is also possible for the recesses not to be in connection with the air gap. The recesses thus extend through the stator in some places in the radial directions. In each case, the electric conductors within the recesses enable the electric machine to be operated efficiently. 
    
    
     
       Hereinafter, the stator described herein and the electric machine will be explained in more detail in conjunction with exemplary embodiments and the associated Figures. 
       In  FIG. 1 , a cross-section through an exemplary embodiment of the stator is shown. 
       In  FIG. 2 , a cross-section through an exemplary embodiment of the electric machine is shown. 
         FIG. 3  shows a cross-section through an example of a stator. 
       In  FIG. 4 , the magnetic flux density within the air gap is plotted for different harmonic components. 
       In  FIG. 5 , the torque over time is plotted for different electric machines. 
       In  FIG. 6 , a cross-section through a further exemplary embodiment of the electric machine is shown. 
     
    
    
       FIG. 1  shows a cross-section through an exemplary embodiment of the stator  20  for an electric machine  21 . The stator  20  has slots  22  for receiving electric windings  23 . In total, the stator  20  has twelve slots  22 . The slots  22  are arranged along the circumference of the stator  20 . Moreover, the slots  22  are open towards an inside  29  of the stator  20 . Within the slots  22 , electric windings  23  are arranged. It is illustrated in  FIG. 1  in which direction electric current flows within the electric windings  23  during operation of the electric machine  21 . The slots  22  extend partially through the stator  20  in radial directions r. The radial directions r each run in parallel to a radius in a cross-section through the stator  20 . The stator  20  has a plurality of laminated sheet packages  33  into which the slots  22  are introduced. 
     Moreover, the stator  20  has at least two teeth  24 , wherein one tooth  24  of the stator  20  is respectively formed between two adjacent slots  22 . The teeth  24  are arranged distributed along the circumference of the stator  20 . In total, the stator  20  has twelve teeth  24 . The electric windings  23  are wound around each tooth  24  along the circumference of the stator  20 . 
     The teeth  24 , around which none of the electric windings  23  is wound, each have a recess  25  extending at least partially through the respective tooth  24 . Thus, every second tooth  24  has a recess  25 . The recesses  25  each extend in a radial direction r, wherein the respective radial direction r runs through the respective tooth  24 . The recesses  25  each may comprise an additional slot  28 . The recesses  25 , like the slots  22 , extend completely through the stator  20  along a longitudinal axis of the stator  20 . Moreover, the recesses  25  or the additional slots  28  extend completely through the stator  20  from an inside  29  towards an outside  30  of the stator  20 . 
     Furthermore, at least two electric conductors  26  which are short-circuited to one another, are arranged within the recesses  25 . In this exemplary embodiment, five electric conductors  26  each are arranged within each recess  25 . The electric conductors  26  have an electrically conductive material, for example, a metal. The electric conductors  26  each do not fill the recesses completely. This means that, apart from the electric conductor  26 , air is arranged within the recesses  25 . At least one of the electric conductors  26  is arranged within the stator  20  such that the electric conductor  26  cannot be electrically contacted from outside the stator  20 . This means that this electric conductor  26  is not accessible from outside the stator  20 . 
     In  FIG. 1 , it is further illustrated, in which direction current flows in the electric conductors  26  during operation of the electric machine  21 . This is achieved in that electric conductors  26  within two recesses  25 , which are opposite to one another in a cross-section through the stator  20 , are electrically connected together. Electric conductor  26  in adjacent recesses  25  are electrically isolated from one another. Moreover, the stator  20  has four further recesses  27 . The further recesses  27  have the same structure as the recesses  25 . The electric conductors  26  within two further recesses  27 , which are opposite to one another in a cross-section through the stator  20 , are electrically connected together. This applies to all of the four further recesses  27 . Thus, the stator  20  has three pairs of recesses  25 ,  27 , in which the electric conductors  26  are short-circuited to one another for each pair. Moreover, in each pair of the recesses  25 ,  27 , the recesses  25 ,  27  are arranged at opposite sides of the stator  20 . 
     In  FIG. 2 , a cross-section through an exemplary embodiment of the electric machine  21  is shown. The electric machine  21  has the stator  20  and a rotor  31  that is movable relative to the stator  20 . The stator  20  has the structure shown in  FIG. 1 . The rotor  31  is arranged as an internal rotor at the inside  29  of the stator  20 . Between the stator  20  and the rotor  31 , an air gap  32  is arranged. The recesses  25 ,  27  of the stator  20  are in connection with the air gap  32 . Moreover, the recesses  25 ,  27  extend completely through the stator  20  in radial directions r, so that the recesses  25 ,  27  are open toward the side of the stator  20  facing away from the rotor  31 . The rotor  31  has  14  permanent magnets  34  arranged at an outside  30  of the rotor  31 . The outside  30  of the rotor  31  is facing the air gap  32 . In the electric machine  21 , the operating wave of the magnetomotive force is different from the fundamental wave of the magnetic flux during operation. This means that it is not the fundamental wave of the magnetic flux that is utilized for generating torque, but that it is the seventh harmonic component of the magnetomotive force. 
     In  FIG. 3 , a cross-section through an example of a stator  20  is shown. The example shown in  FIG. 3  is not an exemplary embodiment. In contrast to the stator  20  shown in  FIG. 1 , no electric conductors  26  are arranged within the recesses  25  in the example in  FIG. 3 . 
     In  FIG. 4 , the magnetic flux density within the air gap  32  is plotted for different harmonic components. The order of the harmonic components is plotted on the x-axis. The magnetic flux density is potted in Tesla on the y-axis. The white bars indicate the magnetic flux density for the example of a stator  20  shown in  FIG. 3 , and the black bars indicate the magnetic flux density for the exemplary embodiment of the stator  20  shown in  FIG. 1 . Thus,  FIG. 4  illustrates the advantages of the exemplary embodiment of the stator  20  shown in  FIG. 1 . 
     In an electric machine having the stator  20  shown in  FIG. 1 , the 7 th  harmonic component of the magnetomotive force is used as an operating wave. This means that the component is utilized for generating torque. Other components of the magnetomotive force have the effect of losses. Consequently, it is advantageous to reduce the magnetic flux density of sub-harmonics and higher harmonics. As compared to an electric machine having the stator  20  of  FIG. 3 , the magnetic flux density for the fundamental wave is significantly reduced in an electric machine having the exemplary embodiment of the stator  20  of  FIG. 1 . Further, the magnetic flux density for the harmonic components of the orders  3 ,  5  and  9  is reduced. Moreover, for an electric machine having the stator  20  of  FIG. 1 , the magnetic flux density of the 7 th  harmonic component is higher than for an electric machine having the stator  20  of  FIG. 3 . Thus, with an electric machine having the stator  20  of  FIG. 1  and the exemplary embodiment of the electric machine  21  of  FIG. 2 , a higher torque may be generated during operation, and the losses are reduced as compared to an electric machine having the stator  20  of  FIG. 3 , which has no electric conductors  26 . Thus, the electric conductors  26  enable an electric machine having the stator  20  of  FIG. 1  and the electric machine  21  of  FIG. 2  to be operated more efficiently than an electric machine having the stator  20  of  FIG. 3 . 
     In  FIG. 5 , the torque over time is plotted for two different electric machines  21 . Time is plotted in seconds on the x-axis. The torque is plotted in Nm on the y-axis. The dashed line shows the torque for an electric machine having the stator  20  of  FIG. 3 . The solid line shows the torque for an electric machine having the stator  20  of  FIG. 1 . For the stator of  FIG. 1 , the torque shows a longer transient response, however in total, the torque has a higher value than for the stator  20  of  FIG. 3 . Thus, the electric conductor  26  within the recesses  25  advantageously enable a higher torque to be generated. 
     In  FIG. 6 , a cross-section through a further exemplary embodiment of the electric machine  21  is shown. In contrast to the exemplary embodiments shown in  FIGS. 1 and 2 , the recesses  25  extend not completely but only partially through the stator  20  in radial directions r. The recesses  25  each are open towards the air gap  32 . Towards an outside  30  of the stator  20  facing away from the air gap  32 , the recesses  25  are closed. 
     This structure to a decrease of the magnetic resistance for the magnetic flux developed by the voltage induced in the electric conductors  26 . Thereby, the losses in the electric machine  21  are further reduced. The torque has the same value as the exemplary embodiment of the electric machine  21  shown in  FIG. 2 . Consequently, the efficiency degree and thus the efficiency for the exemplary embodiment shown in  FIG. 6  is higher than for the exemplary embodiment shown in  FIG. 2 .