Abstract:
A stator for an electric motor, in particular the steering motor of a motor vehicle, comprising a cylindrical stator yoke and a stator star joined therewith and having a number of radially outwardly directed stator teeth, the tooth tips thereof, in the assembly state, resting on the inner circumference of the stator yoke in corresponding connection points. The tooth tips on the stator star side, in the assembly state, in addition to being force-locked or frictionally locked with the connecting points on the stator yoke side in a press-fit, are also integrally bonded thereto.

Description:
[0001]    This nonprovisional application is a continuation of International Application No. PCT/EP2016/051280, which was filed on Jan. 22, 2016, and which claims priority to German Patent Application No. 10 2015 000 769.6, which was filed in Germany on Jan. 26, 2015, and which are both herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates to a stator for an electric motor, in particular for a steering motor of a motor vehicle, comprising a cylindrical stator yoke and a stator star joined therewith and having a number of radially outwardly directed stator teeth, the tooth tips of which rest on corresponding connection points on the inner circumference of the stator yoke when in the joined state. It also relates to a method for producing such a stator, in particular of a steering motor of a motor vehicle. 
       Description of the Background Art 
       [0003]    An electric motor comprises a stator forming the fixed motor part and a rotor forming the moving motor part. In an internal rotor motor, the stator is usually provided with a stator yoke, on which stator teeth are arranged, which project inwards and radially towards the center, and whose free ends facing the rotor form the so-called pole shoe. Coils are mounted on the stator teeth which generate a magnetic field during electromotive operation. 
         [0004]    In order to provide access to the stator teeth from the outside in the production of the stator for the winding of the stator teeth with the coils assigned to them, standard practice is to use a multi-part structure of the stator with stator teeth directed radially outwards from the pole shoe, as is known, for example, from DE 10 2013 003 024 A1 (which corresponds to US 2016/0111929), from DE 10 2013 007 730 A1 or from DE 10 2012 021 132 A1. For this purpose, in the case of the known stator, a laminated core with star-shaped stator teeth (star laminated core) is produced, which teeth are connected to one another by way of pole shoe webs in order to achieve a mechanically stable composite. In this case, the stator is produced from individual, punched stator laminated sheets, in that they are stacked into the star-shaped laminated core in a mechanically stable composite. 
         [0005]    Following the fitting of the stator teeth, which are accessible from the outside, with the windings (coil windings), preferably by means of so-called coil carriers, the star laminated core provided with coils or coil carriers, pushed radially from the outside onto the stator teeth, is inserted into the stator yoke forming a magnetic return ring and is fitted by means of pressing or shrinkage. The stator yoke can also be designed as a laminated core of annular stator laminations (annular laminated core). 
         [0006]    However, the technically advantageous separation between the star-shaped stator component, which is hereinafter referred to as stator star, and the (cylindrical) stator yoke as a further stator component has the acoustic disadvantage that in the case of an electric motor equipped with such a stator, the operating-induced electromagnetic forces excite vibrations throughout the stator. Due to the separation between the stator star and the stator yoke, a resonance frequency occurs in a range, in particular at approx. 1350 Hz, which, when using such an electric motor, in particular in the case of a steering motor, is transmitted as a body sound from engine compartment structures, for example, from the steering system over corresponding structures in the engine compartment into the interior of a motor vehicle where it is perceived as a disturbing air-borne noise. 
       SUMMARY OF THE INVENTION 
       [0007]    It is therefore an object of the invention to provide a stator of the above-mentioned type which is improved in terms of its acoustic behavior, in particular during its use and intended operation in an electric motor, preferably a steering motor of a motor vehicle. Furthermore, a suitable method for producing such a stator is to be provided. Furthermore, an electric motor, in particular a steering motor for a motor vehicle, is to be specified with such a stator. With regard to the stator, this object is achieved according to the invention with the features of claim  1 . With regard to the method, the stated object is achieved according to the invention according to a first variant with the features of claim  6  and according to a second variant with the features of claim  8 . Advantageous embodiments and further developments are the subject matter of the dependent claims. 
         [0008]    With regard to the stator, this stator can have a stator yoke as a cylindrical outer stator component and a stator star as a star-shaped inner stator component having a number of radially outwardly directed stator teeth, which are used to receive coils, in particular also in connection with coil elements of a stator winding. In the joined state of the stator star and the stator yoke, the free end side tooth tips of the stator teeth adjoin corresponding connection points on the inner circumference of the stator yoke. Between at least some of the tooth tips, preferably between all tooth tips, and the respectively corresponding connection point on the inner circumference of the stator yoke, an integral bond is produced in the joined state in addition to the force-locked or frictionally locked connection. The integral bond is preferably realized by means of an adhesive. Alternatively, this can also be produced as a welded connection. 
         [0009]    The invention is based on the consideration that, on the one hand, the acoustic behavior of such a stator with separation between the stator star and the stator yoke is attributable to a resonance frequency of typically less than 1500 Hz perceived within a vehicle as a body sound, and that on the other hand, an increase of this resonance frequency due to the frequency-dependent damping in a vehicle, the sound levels in the vehicle interior can be reduced. In fact this damping is known to occur from a frequency range of approximately 1500 Hz to 2000 Hz, so that an increase in the resonance frequency by a corresponding amount of typically only a few 100 Hz would already lead to a significant improvement in the acoustic behavior in the vehicle. 
         [0010]    A comparatively stiff assembly should be produced as a suitable measure for shifting the resonance frequency of the from the stator star and the stator yoke into the range of 1500 Hz to 2000 Hz. This can in turn be carried out in a reliable and simple manner by an additional connection technique, namely by gluing or welding, for pressing the stator star and the stator yoke. 
         [0011]    In addition to the force-locked or frictionally locked connection between the stator star and the stator yoke, both variants, namely gluing and welding, establish an integral bond between the stator teeth or their tooth tips and the connection points corresponding to the yoke side, so that, as compared to a bond comprising the stator star and the stator yoke, a substantially more rigid bond is formed with only one force-locked or frictionally locked connection. 
         [0012]    In an embodiment, the tooth tips of the stator teeth are formed with suitably wedge-shaped joining contours and the corresponding connection points on the inner circumference of the stator yoke are formed with diametrically opposed joining contours. In this way, on the one hand a position-accurate interfit of stator star and stator yoke is achieved. On the other hand, these joining contours offer comparatively large and in particular full-surface contact of the tooth tips on the corresponding connection points of the stator yoke. The term “abutment” of the star-side tooth tips on the connection points on the yoke side is therefore also understood to include the insertion of the tooth tips in the corresponding connection points, in particular when the corresponding joining locations are formed as a wedge or the like according to the advantageous embodiment. 
         [0013]    The stator yoke can be designed as a cylindrical solid body, while the star-shaped stator component, that is to say the stator star, which is disposed in the stator yoke in the stator mounting state, is formed as a laminated core, for example with alternately closed and at least partially open stator laminations. However, the stator yoke may also be formed as a laminated core of annular stator laminations stacked in the axial direction. 
         [0014]    An especially microencapsulated two-component hard adhesive is particularly preferred as an adhesive for the additional integral bond of the two components of the stator bond made up of stator star and stator yoke, in the region between the stator teeth or their tooth tips and the corresponding connection points on the inner circumference of the stator yoke. Also conceivable is a one-component silicone adhesive. However, this possibly increases the required pressing force when joining the stator star and the stator yoke as compared to the two-component hard adhesive (2-component adhesive, for example GP14). 
         [0015]    The use of such a microencapsulated two-component hard adhesive also offers the advantage that the corresponding adhesive can be applied to the tooth tips of the stator star, and the property is exploited that the adhesive is activated only by pressing the stator yoke on the stator star itself and that it cures at room temperature. Thus, the microencapsulated adhesive can already be applied to the stator teeth thereof, preferably over the entire area, during production of the stator star. 
         [0016]    In order to produce such a stator, the or at least some of the connection points between the cylindrical stator yoke and the star-shaped stator component (stator star) are provided with an adhesive before the joining process, and the stator yoke and the star-shaped stator component are then bonded together and pressed, the stator yoke being applied to the star-shaped stator component or pressed into the stator yoke. 
         [0017]    For example, in the case of a manufactured stator star, the microencapsulated hard adhesive is applied as an adhesive to the free end tooth tips of the radially outwardly directed stator teeth, for example over the entire surface. In this case, the property of such an adhesive is utilized such that it becomes active with regard to its adhesive property only during the pressing of the stator star and of the stator yoke and also cures at room temperature following the bonding and pressing process. 
         [0018]    The advantages achieved with the invention include, for example, the fact that an additional adhesion of a stator star with radially outwardly directed stator teeth and a cylindrical stator yoke results in increased stiffness of a stator joined therefrom and that a particularly low body sound level in the electric motor is achieved during its intended electromotive application and motor operation. This in turn leads to a particularly low airborne sound level within a motor vehicle, in particular in the vehicle interior. 
         [0019]    The production tolerances of the individual stator laminations, which are unavoidable in practice, can also advantageously be used in that, due to the sheet tolerances at the impact points of the stator teeth, sheet gaps occur at the yoke-side connection points into which adhesive material can penetrate during the bonding and pressing of the two stator components (stator star and stator yoke). This leads to a further improvement in the acoustic behavior of the stator and of the electric motor equipped therewith. 
         [0020]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes, combinations, and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
           [0022]      FIG. 1  is a perspective view of a stator star with radial stator teeth with adhesive applied to its free end side tooth tips, 
           [0023]      FIG. 2  is a perspective view of the stator star which is inserted into a cylindrical stator yoke and is connected thereto without stator coils in a frictionally locked and force-locked press-fit, 
           [0024]      FIG. 3  is a diagram of the frequency-dependent oscillation or amplitude profile of a stator without an additional integral bond between the stator yoke and the stator star without coils, 
           [0025]      FIG. 4  is a representation according to  FIG. 3  of the frequency-dependent oscillation or amplitude profile of a stator according to  FIG. 2  with additional integral bond between the stator star and the stator yoke in the form of an adhesive bond with a comparatively soft silicone adhesive, 
           [0026]      FIG. 5  is a representation according to  FIG. 3  of the frequency-dependent oscillation or amplitude profile of a stator according to  FIG. 2  with additional integral bond between the stator star and the stator yoke in the form of an adhesive connection with a two-component hard adhesive (GP  14 ), 
           [0027]      FIG. 6  is a sectional view along the line VI-VI in  FIG. 2 , on a larger scale with plastic material pressed into sheet gaps between a stator tooth and the corresponding yoke-side connection point, 
           [0028]      FIG. 7  is a perspective view of the stator star according to  FIG. 1  with wound coil bodies mounted on its stator teeth, and 
           [0029]      FIG. 8  is a partial perspective view of an electric motor with an internal rotor as well as a stator according to  FIG. 6 , which is wound with coils in the stator yoke in a force-locked and frictionally locked press-fit. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]      FIG. 1  shows a star-shaped stator component, which is hereinafter referred to as stator star  1 , which in the exemplary embodiment is produced as a laminated core of stator laminations  2  stacked one above the other in layers. The stator laminations  2  are stacked on one another to form a central, cylindrical opening  3  in the stacking direction  4  and, for example, are stamped with one another. The stator star  1  is part of the unwound stator shown in  FIG. 2 , and the wound stator shown in  FIG. 7 , of an electric motor shown there. The laminated core of the stator core  1  terminates at the upper side  5  and lower side  6  of said stator core  1 , preferably in each case with at least one stator plate  2  which is closed in the circumferential direction. 
         [0031]    The stator star  1  comprises radially outwardly extending stator teeth  7 , which form a cylindrical pole shoe  8  on the inner side located radially towards the center. The pole shoe  8 , which faces the rotor of the electric motor shown in  FIG. 8 , is only partially closed on the circumferential side in the stacking direction  4 , with the formation of gaps  9  on the pole shoe side in order to reduce a magnetic short circuit. 
         [0032]    The stator teeth  7  are provided on the free end side with wedge-shaped tooth tips  10 , forming contact surfaces  11  which are located to the left and right of a tooth tip wheel. An adhesive  13 , preferably a microencapsulated two-component hard adhesive, is applied to these contact surfaces  11  and thus to the tooth tips  10  after or in the course of the manufacture of the stator star  1 . In this case, both contact surfaces  11  or even only one of the contact surfaces  11  of the respective tooth tip  10  can always be coated with the adhesive  13 . 
         [0033]      FIG. 2  shows the stator  14 , which is joined in a force-locked/frictionally locked press-fit from the stator star  1  and a stator yoke  15  by means of a pressing operation, wherein additionally, by means of the microencapsulated adhesive  13  applied to the tooth tips  10  of the stator teeth  7 , an integral bond between the stator star  1  and the stator yoke  15  is made. The integral bonds are produced by means of the adhesive which cures after the joining process between the tooth tips  10  and the connection points  16  corresponding thereto, on the inner circumference  17  of the stator yoke  15 . 
         [0034]    The stator yoke  15  can be a cylinder jacket made of solid material or else made from stacked magnetic return ring laminations. In the assembled state, the windings, which, again, are not visible here, are laid around the stator teeth  7  of the stator star  1 . Before the stator star  1  and the stator yoke  15  are joined, according to  FIG. 7 , the windings are mounted on winding carriers  19  as coils  18  and with said carriers  19 , are placed on the stator teeth  7 . Each of the frame-like winding carriers  19  carries a coil or coil winding  18  as part of the stator winding. In each case, two successive coils  18  are connected continuously and form a coil pair with the coils  18  in a series connection. The coil pairs are each contactable via two coil ends  20 ,  21 . The overall twelve coil ends  20 ,  21  shown are oriented axially, i.e., in the axial direction A (direction of the motor axis), for further contacting by means of an interconnection element  22  which can be seen in  FIG. 8 . In electromotive operation, the energized windings produce the stator-side magnetic field, which interacts with permanent magnets of the rotor  23  of the brushless electric motor  24  rotating around the central stator or motor axis A. The small interconnection element  22  serves for contacting and interconnecting the coil ends  20 ,  21 . 
         [0035]      FIGS. 3 to 5  show in each case three oscillation curves over a frequency range from 0 Hz to 3000 Hz, which according to  FIG. 2 , were metrologically measured by a laboratory test upon introduction of oscillations on an unwound stator  14  without coils. The mechanical vibrations were introduced at the outer side of the stator yoke  15  by means of a suitable device in the form of a so-called micro-shaker. For this purpose, the stator  14  was freely suspended by means of a laboratory cord. The waveform of the introduced vibrations was white noise in the frequency range from 50 Hz to 5000 Hz. The generated vibrations were recorded on the outer side of the stator yoke  15  by means of three measurement sensors (uniaxial sensor). In this case, the measuring positions were radially aligned with stator teeth  7  in the stator star  1 , the sensors being arranged offset by 60° (angular degree). 
         [0036]      FIG. 3  shows the frequency-dependent oscillation curve, which is metrologically measured by means of the three measurement sensors. The three measurement sensors are therefore each assigned one of the three waveforms shown. The same is true for the metrologically measured waveforms shown in  FIGS. 4 and 5 . While the waveforms in  FIG. 3  show a standard and thus conventional stator without an additional integral bond between the stator star  1  and the stator yoke  15 ,  FIGS. 4 and 5  show the metrologically identical situation in the case of a stator  14  with an additional integral bond between the stator star  1  and the stator yoke  15 .  FIG. 4  shows the use of a comparatively soft single-component (1 k) silicone adhesive (type Q3 6611; Decosil) as an adhesive between the stator-side tooth tips  10  and the corresponding yoke-side connection points  16 .  FIG. 5  shows the measurement-technical result when using a two-component hard adhesive (2-component adhesive GP14; hard). This is a microencapsulated adhesive which advantageously unfolds its adhesive effect after prior application of the adhesive  13  to the tooth tips  10  of the stator star  1 , only during the joining of the stator star  1  and the stator yoke  15  in a pressing process, and then cures at room temperature. 
         [0037]    According to  FIG. 3 , significant oscillation amplitudes can be seen at approx. 1660 Hz. The reason for the deviation of the resonance frequency that is expected there at approximately 1350 Hz is due to the fact that the stator used as a test was designed without coils on its stator star  1 . On the basis of the comparison of the signal profiles according to  FIGS. 3 to 5 , however, it can be clearly seen that the additional integral bond between the stator star  1  and the stator yoke  15  causes a displacement of this significant resonant frequency by 320 Hz to a frequency of 1980 Hz ( FIG. 4 ) when using the silicone adhesive, and that when using the preferred microencapsulated hard adhesive, the resonance frequency is shifted by a frequency of about 600 Hz to an even higher frequency of about 2250 Hz. 
         [0038]    A further increase in amplitude at approximately 1250 Hz of the stator produced without additional integral bond is also detectable. This increase in amplitude at about 1250 Hz, illustrated in  FIG. 3 , was also shifted toward higher frequencies when using an additional integral bond, namely when using a silicone adhesive, by about 100 Hz to 1350 Hz, and when using the hard adhesive, by about 250 Hz to 1500 Hz, as is again illustrated in  FIGS. 4 and 5 , respectively. 
         [0039]    In the described experimental modal analysis, i.e., excitation by means of a micro-shaker as well as measurement of the generated body sound on the stator test specimen, it is thus shown that the occurring resonance frequency increases by approximately 600 Hz by means of a hard-curing, two-component adhesive. As already mentioned, no coils and no decoupling ring were mounted on the stator  14  during the laboratory measurement, which is the reason for the deviation of the resonant frequency as compared to typical, series production motor measurements. In the measurement result shown in  FIG. 3 , this deviation is approximately 310 Hz as compared to the typical resonance frequency of 1350 Hz mentioned above. Nevertheless, the frequency due to the additional integral bond between the stator star  1  and the stator yoke  15  is clearly shifted in the acoustically comparatively uncritical range over 1500 Hz that was mentioned above. This resonance frequency shift, which is positive overall in terms of the noise behavior of the electric motor  24 , at least in its perception within the interior space of a vehicle, is attributable to the significantly increased stiffness of such a stator  14  achieved by the additional integral bond as compared to a stator or electric motor with only pressed stator stars and stator yoke. 
         [0040]      FIG. 6  shows, in a not to scale view, a typical integral bond between one of the teeth  7  of the stator star  1  and the stator yoke  15  at the corresponding yoke-side connection point  16  with the tooth tip  10  of this stator tooth  7 . Due to the practically unavoidable tolerances which are typical during production and manufacture, the stator laminations  2  arranged one above the other in the stack of laminations in the stack direction  4  can be seen not completely aligned with one another in the region of the respective tooth tips  10 . This leads to the formation of pockets or lamination gaps  25  whose expansion in the axial direction A of the sheet thickness of the respective stator plate  2  and expansion in the radial direction R correspond to the respective tolerance dimension. 
         [0041]    In the course of the joining process, namely the pressing process of the stator yoke  15  with the stator star  1 , adhesive material has entered in the lamination gaps or pockets  25  so that these are at least partially filled with adhesive  13 . This filling of the production-related, pocket-like lamination gaps  25  between the stator teeth  7  of the stator star  1  and the connection points  16  of the stator yoke  15  during production of the additional integral bond between these stator components  1 ,  15  are thus used to improve the acoustic behavior of the stator  14  and of the electric motor  24  equipped with the latter in a positive and amplifying manner. 
         [0042]    The invention is not limited to the embodiments described above. Rather, other variants of the invention can also be derived from those skilled in the art without departing from the scope of the invention. In particular, all the individual features described in connection with the exemplary embodiments can also be combined with each other in another manner without departing from the subject matter of the invention.