Patent Publication Number: US-2022216766-A1

Title: Electric motor

Description:
The present invention refers to an electric motor, in particular to an axial-flow electric motor. The invention also refers to the electric vehicle mounting the motor. 
     Electric vehicles, especially high-performance ones, have very powerful electric motors. Universally the motor shaft is coupled to the stator via a ball or roller bearing, which is not lubricated and is highly stressed. That&#39;s why after a certain mileage the bearing must be replaced. 
     The maintenance, which is expensive and unwanted, is also accelerated by another problem, typical of these motors: the bearing is at the center of the motor, where it is very difficult to achieve adequate cooling. Thermal stresses too shorten the life of the bearing. 
     The main object of the invention is to improve the present state of the art. 
     Another object of the invention is to make a motor that does not suffer from the aforementioned problems. 
     Another object of the invention is to make a motor with less maintenance. 
     Another object of the invention is to make a motor with better cooling. 
     In particular, the invention is directed to an axial-flow electric motor, i.e. a motor having windings that generate a magnetic flux with a polar axis parallel to the rotation axis of the rotor. This type of motor has more complex structure than radial-flow motors but, the power being the same, it is lighter and smaller. 
     At least one of these objects is achieved by what is stated in the attached claims; advantageous technical characteristics are defined in the dependent claims. 
     An electric motor is proposed comprising: 
     a rotor, 
     a shaft integral with the rotor to transfer torque to a load, 
     a stator crossed coaxially by the shaft, 
     a plain bearing (or bush) placed between the stator and the shaft, and 
     a lubricant fluid circuit configured to transport lubricant fluid and wet a contact surface between the stator and the shaft with the fluid. 
     In this way, between the stator and the shaft there forms a film of lubricating fluid which not only guarantees the relative rotation between the stator and the shaft with reduced friction but also removes heat from this interface. Another advantage is that the oil also cools the shaft and consequently heat can be removed from the rotating disks and magnets, which suffer from high temperatures. 
     The circuit may be built or composed in various ways. 
     According to a preferred embodiment, the circuit comprises a (first) channel inside the shaft with a(n) (first) outlet on said surface; from such outlet the fluid can arrive on and/or return from said surface. So the circuit structure is simpler and the shaft is exploited to convey the lubricating fluid to the plain bearing, which is in a little accessible point. 
     The lubricating fluid can come out of the outlet, wet the contact surface and come out from the bushing e.g. dripping down the stator. 
     In a variant, the circuit comprises a second channel inside the shaft with a second outlet on said surface spaced from the first outlet of the shaft; the circuit being configured in such a way that the fluid exits from the first outlet going onto said surface and enters the second outlet to leave said surface. 
     In a variant, the circuit comprises a (second) channel inside the plain bearing with a (second) outlet on said surface spaced from the first outlet of the plain bearing; the circuit being configured so that the fluid exits from the first outlet of the plain bearing moving onto said surface and enters the second outlet of the plain bearing to leave said surface. 
     According to a preferred embodiment, the circuit comprises a channel inside the plain bearing with an outlet on said surface. From said outlet the fluid can arrive onto—and/or return from—said surface. 
     In a variant, a or each channel inside the plain bearing is a pass-through channel which radially passes through the thickness of the plain bearing. 
     In a variant, the or each channel inside the shaft and/or the plain bearing is connected to, or in general the circuit comprises, a reservoir of lubricating fluid, which advantageously can e.g. act as a purification and/or cooling environment. 
     Advantageously, the reservoir of lubricating fluid is comprised in a casing of the motor, e.g. a cup, and the casing is preferably externally finned in correspondence of the reservoir. 
     In a variant, the motor comprises a pump for circulating the lubricant fluid within the circuit. In particular, the pump is connected to the shaft to be operated by the shaft itself. The pump could also be electric and/or external to the motor. 
     The pump could also bring the fluid directly to a cooling-down radiator. 
     Another aspect of the invention refers to an electric vehicle mounting the motor, e.g. a car, a truck, a lorry, or a ship. In these cases the motor must have substantial power and/or with considerable stress, ergo the advantages of the invention are particularly significant. 
    
    
     
       Further advantages will become clear from the following description, which refers to a preferred embodiment of a motor wherein: 
         FIG. 1  shows a partial schematic view of an electric motor; 
         FIG. 2  shows a partial schematic view of a second electric motor; 
         FIG. 3  shows a partial schematic view of a third electric motor; 
         FIG. 4  shows a cross-sectional view of a fourth electric motor. 
     
    
    
     Equal numbers in the figures indicate equal or substantially equal parts. 
       FIG. 1  partially illustrates an electric motor  10  which comprises a shaft  14  integral with a rotor (not shown) and rotatable about an axis X. The shaft  14  coaxially crosses a stator  12  with which it couples by sliding on a plain bearing  16  arranged between the stator  12  and the shaft  14 . 
     To transport a lubricating fluid (e.g. oil) and wet with the fluid a contact surface S between the stator  12  and the shaft  14 , the shaft  14  comprises at least one internal channel  18  with an outlet  20  on the surface S. E.g. the channel  18  comprises a central axial segment, and one or more radial segments which from the central segment reach the lateral surface of the shaft  14 . 
     From the outlet  20  the fluid can arrive onto—and/or return from—the surface S and form therein a film  24  of lubricant. 
     The plain bearing  16  comprises an internal channel  22  which radially crosses its thickness. The channel  22  has an outlet on the surface S for carrying fluid onto the surface S or to receive it from there. 
     The channel  18  and the channel  22  therefore form a circuit capable of circulating the lubricating fluid on the surface S. 
       FIG. 2  shows a different embodiment of such circuit. 
     The shaft  14  comprises a first internal channel  18  with an outlet  20  on the surface S and a second internal channel  30  with an outlet  32  on the surface S. The outlets  32 ,  20  are spaced from each other in the direction of the X axis 
     From the outlet  20  the fluid can arrive onto the surface S, forming a film  24  of lubricant, and can exit the channel  32 . 
       FIG. 3  shows another embodiment of the fluid circuit. 
     Here the shaft  14  does not comprise internal channels. 
     The plain bushing  16  comprises a first radial internal channel  40  with an outlet  42  on the surface S and a second radial internal channel  44  with an outlet  46  on the surface S. The outlets  42 ,  46  are spaced from each other along the direction of the X axis. 
     From the outlet  42  the fluid can arrive on the surface S, form a film  24  of lubricant thereon, and exit from the channel  44 . 
     The fluid circuits of  FIGS. 1-3  may be e.g. 
     closed on a pump (not shown), capable of pushing the fluid within the channels; and/or 
     connected to suck and/or bring fluid back from/to a reservoir of fluid, advantageous because it ensures an uninterrupted fluid supply and because it allows cooling effectively the heated fluid arriving from the film  24 . 
       FIG. 4  shows overall an electric motor MC which accomplishes completely the scheme of  FIG. 1 . 
     The motor MC is contained in a casing  60  from which a shaft  40 , rotatable about an axis X, protrudes. The shaft  40  is integral with two rotors  66 , from which it receives rotary torque, and coaxially crosses a stator  62 , responsible for the rotation of the rotors  66 . 
     The stator  62  e.g. comprises windings  64  for generating a magnetic field parallel to the axis X and capable of striking permanent magnets  68  mounted on the rotors  66 , which are facing—and coaxial to—opposite sides of the stator  62 . 
     The shaft  70  is slidingly coupled with the stator  62  by means of a plain bearing  90  placed between the stator  62  and the shaft  70 . 
     The shaft  70  comprises an internal channel formed by a central coaxial segment  74 , and one or more radial segments  72  which starting from the central segment  74  reach the lateral surface of the shaft  70  in contact with the plain bearing  90 . The central segment  74  also communicates with one or more radial segments  76  which starting from the central segment  74  reach the lateral surface of the shaft  70  externally to the plain bearing  90  and to the rotors  66 . The output of the one or more radial segment  76  is connected with a pump  80  supplied through a conduit by a reservoir of lubricating fluid  92  located at the base of the casing  60 , which functions as a well-known oil pan in an internal combustion engine. Preferably the base of the casing  60  is finned, to better dissipate the heat of the fluid. 
     What described above allows transporting the lubricating fluid (e.g. oil) and wet with it the contact surface S between the stator  62  and the shaft  70 . 
     In particular, the pump  80  circulates the fluid by withdrawing it from the reservoir  92 , and injects it into a channel  76 . From here the fluid runs through the channels  74  and  72 , to arrive on the surface S where it spreads to form a thin film. When the fluid has covered the lateral surface of the plain bearing  90 , it falls by gravity into specific ducts which are located under the walls of the stator  62  and returns to the reservoir  92 . 
     The solutions shown in  FIGS. 1, 2 and 3  can be used alone or in combination.