Abstract:
The invention relates to a synchronous motor with permanent magnets comprising a rotor ( 110 ) provided with permanent magnets a winding ( 120 ) formed by overlapping coils located inside a slotless stator ( 100 ), characterized in that the winding coils ( 120 ) are regularly distributed all around the 360° of the inside surface of the stator ( 100 ) and in that the ends of the coils are designed so as the winding has the same thickness throughout and in that the ends of the winding are at least partially inside the slotless stator ( 100 ).

Description:
[0001]    This application claims priority benefits of European Patent Application Number 10195053.3 filed Dec. 15, 2010, the entire disclosure of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates a synchronous motor to with permanent magnets comprising a rotor provided with permanent magnets, a winding formed by overlapping coils located inside a slotless stator. 
         [0003]    The main objective of the current invention is a synchronous motor with permanent magnets provided with a winding distributed continuously and homogeneously inside the stator without slots to achieve the minimum change of the torque capacity all around the movement of the rotor. Simplicity of mounting and recycling are also added values taken into account in this invention. 
       BACKGROUND OF THE INVENTION 
       [0004]    The present invention is based on the Laplace force equation (F=i(l̂B)) where it is stated that a current ‘i’ crossing a conductor is generating a force ‘F’ perpendicular to the conductor and the magnetic flux ‘B’ that is also crossing the conductor. 
       SUMMARY OF THE INVENTION 
       [0005]    The motor according to the present invention is characterized by the characterizing part of claim  1 . 
         [0006]    As the two ends of the winding do not present the usual protuberances due to the overlapping of the coils turns, the stator may be extended to face the ends of the winding. So we achieve a homogeneous torque capability, as no difference in reluctance appears and so the torque is only dependent on the winding designed. 
         [0007]    It is also necessary to adjust perfectly the wire diameters of the coils with the space available for the cooper that fulfills any possible lack of air that would not make the torque constant. Diameter where magnets are placed and internal diameter of the winding are also relevant in the design to achieve the optimal distribution of the wires. The design not only is taking into account the wires of the coils but also the thickness of the space for the copper so that it is optimized not to waste more quantity of magnet than required but also the quantity of cooper to achieve the maximum possible torque per volume available. 
         [0008]    Although some concepts are similar with the patent EP 0′123′347, this invention differs slightly from it in the way that the winding is being surrounded by laminated electrical steel or equivalent material to increment efficiency. 
         [0009]    According to a preferred embodiment the shape of the ends of the coils is deformed in the cross points of the coils by keeping their cross section surface constant and in that only two coils turns are crossed at a same location of the ends of the coils allowing to obtain said annular extensions. 
         [0010]    After a deformation of the coils in a way that the section of the winding all around the circumference is constant and that only two coils turns are crossed at a same location of the ends we have a winding with a constant width all along his length located inside the stator. Consequently, the length useful for the force of the wires to be applied as a torque is higher and consequently the power density. 
         [0011]    Further, winding heat dissipation through the stator is much better and although some increment of the resistance may appear due to the length increment of the coils, it can be admitted due to the increment of useful magnetic length and improvement in the dissipation. 
         [0012]    The use of windings having the same thickness throughout is possible for radial magnetic flux motors as well as for axial magnetic flux motors as defined in claims and as it will be described hereafter. 
         [0013]    According to a feature the winding may be made by graphene material. 
         [0014]    Other features are listed in the dependent claims. 
         [0015]    Preferred embodiments of the present invention will be described with reference to the attached figures 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a radial cross section of a radial magnetic flux motor; 
           [0017]      FIG. 2  is a usual representation of a motor winding diagram; 
           [0018]      FIGS. 3A and 3B  are an axial cross section and a side view of a prior art radial magnetic flux motor; 
           [0019]      FIGS. 4A and 4   b  are an axial cross section and a side view of a radial magnetic flux motor according to the present invention; 
           [0020]      FIG. 5  shows a plane and a side view of a prior art coil; 
           [0021]      FIG. 6  shows a plane and a side view of a coil according to the present invention; 
           [0022]      FIG. 7  is a radial cross section of the end the winding of a radial magnetic flux motor according to the present invention; 
           [0023]      FIG. 8  is a perspective view of a winding according to the present invention relating to a radial magnetic flux motor; 
           [0024]      FIG. 9  is a perspective view of a tubular slotless stator relating to a radial magnetic flux motor; 
           [0025]      FIG. 10  is an axial cross section of a prior art axial magnetic flux motor 
           [0026]      FIG. 11  is an axial cross section of axial magnetic flux motor according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    In  FIG. 1 , a radial cross section of a radial magnetic flux motor is shown. We see the tubular stator  1 , the tubular winding  2 , the permanent magnets  3  placed on the lateral surface of the rotor  4 . The windings of the three electrical phases U, V, W are represented all around the tubular winding  2  periphery. 
         [0028]    A perfect regular distribution of wires all around the inside surface of the stator allows to obtain a powerful and high efficiency motor able to produce a constant power torque all around his movement. Although there are some other patents like EP 0′159′069 which shows magnetic motor solutions similar to our invention in flat execution or EP 0′221′594, in our invention we distribute the wires perfectly all around the any possible position of the circumference so the torque produced is always constant. 
         [0029]    Further, standard designs in slotless or slotted motors, normally align the length of the magnets with the length of stator. As mainly the kind of winding used is overlapped (it allows higher range of speed due to the lower number of poles required), the turns of the coils for different phases of the motor are being crossed ( FIG. 2 ) and so they increment the thickness of the winding at his ends creating two protuberant annular parts. 
         [0030]    In order to increase the useful area which is in front of the magnets and not to align the wires there so that the torque produced for the current crossing the wires is maximum, the crosses of the turns of the coils are being done in what we call ‘end of the coils’ out of the stator. However, it implies that the end of the winding increases his volume in standard designs and stator cannot be placed there. It has a significant importance as the heat being produced in this part of the motors is hardly evacuated. Some inventions like patent EP 1′715′562 capsulate the windings to help the heat go out of the motor although the efficiency of them cannot be compared with heat dissipation of the iron or aluminum. 
         [0031]    Being conscious of this behavior, and of the importance to have the coils of the winding close to the housing (normally aluminum) or to the stator, the present invention shows a way to design the winding optimizing this phenomenon. 
         [0032]    A comparison of volumes in standard designs and our invention is shown in  FIGS. 3A ,  3 B,  4 A and  4 B. 
         [0033]    In  FIGS. 3A and 3B  they are represented: a tubular slotless stator  10 , a tubular winding  12  with the annular protuberances  12 A located in the crossing of the turns of the coils and the rotor with the permanent magnets  11 . 
         [0034]    In  FIGS. 4A and 4B  they are represented the same elements: a tubular stator  100 , a tubular winding  120  without the annular protuberances located at the crossing of the turns of the coils and the rotor with the permanent magnets  110 . 
         [0035]    It is easy to see that in  FIGS. 4A and 4B  the stator  100  is covering nearly all the winding  120 . Indeed for an overall diameter D and length L which are the same for both motors we have a length stator Ls′&gt;Ls, a length of the magnets Lm′&gt;Lm thanks to the removal of the annular protuberances  12 A. To achieve this goal we have to deform the ends of the coils and to cross the turns of only two coils at same location. 
         [0036]    Modifying the shape of the coils when being made by press deformation, we must keep the surface of the section (b×a) of the coil constant but without the need of keeping values of ‘b’ and ‘a’ constants. So if we modify these parameters all along the coils, we are able to achieve longer coils but in total winding having the same section. ( FIGS. 5 and 6 ). 
         [0037]    In  FIG. 5  a usual coil is represented with a rectangular section. The length of the coil before the turn is ‘l’, the height of the turn is ‘h’ and the dimensions of the rectangular section in the entire length of the coil are ‘a’ and ‘b’. So the surface of the coil section is equal to A=‘b’×‘a’. As it is important to keep the value A constant, in  FIG. 6  the turn coil is deformed so that even the parameters ‘a’′, ‘h’′ are modified the surface A′ of the section in turn coil is equal to A. 
         [0038]    The objective is to reduce the thickness of the coils fundamentally at the point where the turns of two coils are being crossed in the winding diagram ( FIG. 2 ). So we do not increase the radial thickness of the winding and it is kept constant all along the winding length. That allows increasing the length of the stator, and obtaining more torque as more length is useful for the torque. 
         [0039]    Another advantage is the improvement of the heat evacuation as the ends of the coils are in contact with stator material instead of the air. Stator material is much more conductive for the heat and so heat will be evacuated much easily. 
         [0040]    Depending on the wires used, and section required, coils of the winding will be deformed in order to adjust his profile will the following coil next to it. The objective is that the crosses are only being experimented by two different coils. Taking for example the wire distribution of the  FIG. 1 , one possible shape of the ‘end of the coil’ could be the one shown in  FIG. 7 . This particular shape of the turns of the coils makes possible to have the same thickness all along the winding. It can be seen that there are two crosses all around a circumference. Never the turns of the coils of the three coils have a coincidence in any point. There are maximum two. It is clear that the height of the coil is being modified as shown in FIG.  6  and the copper volume is the same as we let the coils increase in axial direction. So thickness of the winding is constant all along the stator as internal and external diameter of the winding does not suffer any increment of cupper. For this reason the length of the stator can cover all the ends of the coils. Winding is covering a volume of a perfect cylindrical. This particular property allows to construct the stator not only with magnetic steel, but also with magnetic powder like in EP 1′715′559. It is also possible to use a magnetic wire coiled to produce the tubular stator as described in EP 0′313′514. Such a coiled stator reduce the cost for producing stators significantly as it uses less quantity of raw material. 
         [0041]    This type of construction has several advantages. It simplifies significantly the structure of the winding, as it can be mounted separately from the stator, and so the assembly is much easier. In an opposite way, whenever needed to destroy, it is easy to separate the cooper of the winding from the stator. It is possible then to do a recycling much efficient. 
         [0042]      FIG. 8  shows a tubular winding according the invention. In  FIG. 9  a slotless tubular stator is shown. It is made by stacking punched ring shaped laminations of magnetic steel. The press used to punch slotless rings is less expensive as his live is increased. 
         [0043]    In  FIG. 10  an axial cross section of axial magnetic flux motor is shown. A disk shape rotor  50  is provided with permanent magnets  80  hold by magnet holders  81 . The slotless stator comprises two annular parts  60  made by magnetic material laminations. The winding  60  comprises two annular parts presenting at their ends embossed parts  71  due to the crossing of the turns of the coils. 
         [0044]    In  FIG. 11  an axial magnetic flux motor according to the present invention is shown. A disk shape rotor  50 ′ is provided with permanent magnets  80 ′ hold by magnet holders  81 ′. The slotless stator comprises two annular parts  60 ′ made by magnetic material laminations. The windings  60 ′ have the same thickness throughout. By comparing the motors having the same overall diameter and length it is obvious the active surface of the winding is greater facing a greater surface of the stator and a greater surface of the permanent magnets. So we have a more powerful motor. The stator as previous may be made by any kind of magnetic material. 
         [0045]    The wires of the winding may be made by using graphene. This material has a bigger current density value than copper, so more power can be obtained. Further graphene presents a higher thermal conductivity than copper and so it will be easier to transfer the heat out of the motor.