Abstract:
An in-wheel motor having an inner stationary portion (the stator), and an outer rotating portion (the rotor) that rotates around the stator and drives a wheel directly attached to the rotor. The stator may comprise an inner support structure around which a plurality of magnets having windings are disposed in a circumferential fashion. The rotor circumferentially surrounds the stator, and includes permanent magnets placed at an interval along a surface of the rotor. An intermediate layer between the rotor and the stator is comprised of a bearing that allows movement of the rotor relative to the stator. By attaching a wheel directly to the outer surface of the rotor, a compact and efficient wheel-mounted electrical motor may be provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. §119(d) to a corresponding patent application filed in India and having application number 1226/CHE/2009, filed on May 27, 2009, the entire contents of which are herein incorporated by reference. 
     BACKGROUND 
     Due to continued increases in the price of petroleum-based fuels, and concerns about by-products of burning petroleum-based fuels, electric and hybrid cars have become more popular with purchasers and more economical as well. 
     An electric car is a type of alternative fuel vehicle that utilizes an electric motor and motor controller instead of an internal combustion engine. A hybrid car is a type of alternative fuel car that includes both an electric motor or motors and an internal combustion engine. Currently, in most cases, electrical power is stored and derived from battery packs carried on board the vehicle. Fuel cells are also being used to power electrical motors. 
     In a pure electric vehicle, with no corresponding internal combustion engine, an electric engine replaces the internal combustion engine, providing a central power plant to provide power to a mechanical distribution system (a transmission) that then transfers the power to disparately placed wheels. 
     A similar system is used in hybrid vehicles, with the exception that both an electric motor and an internal combustion motor (albeit smaller than an internal combustion motor for an internal combustion-only vehicle) work together to perform the function of the traditional internal combustion motor. As in the case of the pure electric vehicle, a mechanical distribution system is utilized to transfer power from the centralized motor compartment to the disparate positions of the wheels. 
     In a conventional electric motor centralized at an engine compartment, the outer casing (the stator) is stationary while a rotating portion inside the stator (the rotor) rotates to generate mechanical energy. The transmission of the mechanical energy from the electrical engine in the centrally placed engine compartment of the vehicle to remote load locations at the wheels introduces losses into the system that reduce the efficiency of the electrical vehicle, and thereby decreases the overall range of an electrical vehicle. 
     Accordingly, advances in electric vehicle design are needed to further improve energy efficiency and reduce manufacturing and/or total ownership costs so as to increase the availability of electric and hybrid vehicles to consumers around the world. 
     SUMMARY 
     Disclosed herein is an in-wheel motor comprising an inner stationary stator including a plurality of magnets having windings, the magnets arranged at an outer circumference of the stator, an outer rotor surrounding the inner stator and including a plurality of magnets arranged at a circumference of the rotor, and a bearing layer positioned radially between the stator and the rotor for allowing rotational movement of the rotor relative to the stator, and for distributing forces applied to the outer rotor. A plurality of switches may be arranged correspondingly to the plurality of windings, and a controller may be disposed for applying a switching pattern to the switches to cause the rotor to rotate in a first or second axial direction. 
     A speed of the rotor may be controlled by varying a frequency of the switching pattern, and a torque of the rotor may be controlled by varying a pulse width of the switching pattern. An encoder may be attached to the rotor to determine a current position of the magnets on the rotor relative to the windings of the stator to aid in determining a proper switching pattern to apply to the switches. 
     The bearing layer may be comprised of bearings. In one example, the bearings could be a plurality of rolling ball-bearings. 
     The disclosed in-wheel motor could be used as a wheel on a train so as to cause the rotor to rotate over a metal rail. Alternately, a rubber tire may be attached to an outer circumference of the rotor to allow the wheel to be used on a roadway material such as pavement or cement. 
     Also disclosed herein is an in-wheel motor having an inner stationary stator including a plurality of magnets including windings, the magnets arranged at an outer circumference of the stator, an inner support ring coupled to the magnets and extending in a direction parallel to a central axis of the in-wheel motor away from the magnets, an outer rotor surrounding the inner stator and including a plurality of magnets arranged at a circumference of the stator, a rotor projection portion extending in the direction parallel to the central axis of the in-wheel motor so as to surround the inner support ring; and a bearing layer positioned radially between the inner support ring of the stator and the projection portion of the rotor allowing rotational movement of the rotor relative to the stator, and for distributing forces applied to the outer rotor. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a perspective view of an in-wheel motor according to one embodiment; 
         FIG. 2  is a perspective view of a winding according to one embodiment; 
         FIG. 3  is a diagrammatic side-view of an embodiment of an in-wheel motor showing a magnetic flux field created by passing current through a winding; 
         FIG. 4  is a timing diagram setting forth an example method of driving windings of a stator of an in-wheel motor; 
         FIG. 5  is an example circuit diagram for producing drive signals to drive the windings of a stator of an in-wheel motor; 
         FIG. 6  is a perspective view of an in-wheel motor having rolling bearing elements between the rotor and the stator according to an embodiment; 
         FIG. 7  is a perspective view of an alternative bearing arrangement according to an embodiment; and 
         FIG. 8  is a reverse perspective view of the alterative bearing arrangement of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
       FIG. 1  sets forth an illustrative in-wheel motor  100 . The in-wheel motor  100  is comprised of two main components, a stationary stator  104  and a rotor  110 . The rotor  110  is positioned around the circumference of the stator  104  such that it is capable of rotation around the stator  104 . The stationary stator  104  is formed around the outer circumference of a circular mechanical support element  102 . A plurality of electromagnets  106  are positioned along an outer circumference of the stator  104 . The rotating rotor  110  circumferentially surrounding the stator  104  includes a number of magnets  112 . A bearing  114 , as discussed in more detail in regard to  FIG. 6 , is formed between the rotor  110  and the stator  104  to support the axial rotation of the rotor  110  relative to the stator  104 . As discussed in more detail below, the electromagnets  106  of the stator  104  can be energized in a controlled fashion to drive rotation of the magnetic rotor  110 . 
     The mechanical support element  102  could be formed in the shape of a ring, as shown in  FIG. 1 . Alternately, any shape could be used, including, for example, a hub-and-spoke shape in which the stator  104  is supported by spokes connecting to a central hub. The mechanical support element  102  may be formed of any rigid material that would provide sufficient rigidity to support the weight of a vehicle. For example, a composite, a solid metal, or a metal alloy material could be used. Alternatively, a rigid plastic material could be used, or a heterogeneous mix of any two or more materials. Other examples are possible as well. 
     A plurality of electromagnets  106  are placed along an outer circumference of the mechanical support  102  and stator  104 . Although  FIG. 1  shows a large number of electromagnets  106  along the outer circumference of the support  102 , any number of electromagnets  106  generally greater than two could be used depending on the particular application, including the desired speed and torque for the application. 
       FIG. 2  sets forth a more detailed view of the electromagnets  106 . In this embodiment, each electromagnet  106  is comprised of an E-shaped core  202  having a base  204  and a first outer finger  206  and second outer finger  210  extending perpendicularly from the base  204 . A third central finger  208  is formed between the two other fingers also extending perpendicularly from the base  204 . A winding  108  may be formed around the central finger  208  and connected to a switch (not shown) for supplying power to the winding  108 . The electromagnet  106 , when energized, imparts an electromagnetic force on the rotor  110 , which is spaced apart from the electromagnet  106 , as described in more detail in the embodiments below. 
     In other example embodiments, different shaped electromagnetic cores could also be used, including, for example, a bar-shaped, an F-shaped, or a C-shaped core. An advantage of the E-core is that it provides substantial room to bring in high current lead wires, and provides good heat dissipation. The E-shaped core  202  could be formed of an iron alloy, a cobalt alloy, ferrite, or any other suitable material. While  FIG. 2  illustrates equally-sized fingers  206 - 210 , one or more of the fingers  206 - 210  may differ in width and/or length. 
     Returning to  FIG. 1 , the in-wheel motor  100  comprises the rotor  110  circumferentially surrounding the stator  104 . As previously mentioned above, the rotor  110  includes a plurality of periodically placed magnets  112 . The magnets  112  interact with the magnetic flux created by the stationary electromagnets  106  of the stator  104  to impart torque on the magnets of the rotor  110  and cause the rotor  110  to rotate in one of a clockwise or counter-clockwise direction relative to the stator  104 . The magnets  112  may be, for example, permanent magnets formed of a ferromagnetic material, including iron, cobalt or nickel. Alternatively, or additionally, the magnets  112  could be rare-earth magnets such as samarium-cobalt or neodymium-iron-boron. Other appropriate materials could also be used. While  FIG. 1  illustrates an in-wheel motor  100  having an equal number of electromagnets  106  and magnets  112  with each pair aligned in a radial direction, such an arrangement is not necessary. In another embodiment the number of electromagnets  106  could be unequal to the number of magnets  112 , and spaced in such a way that at least some of the magnets  112  are always un-aligned with some of the electromagnets  106 , in order to avoid potential starting problems. 
       FIG. 3  illustrates a magnetic flux field  302  generated by the electromagnets  306  in an example embodiment of an in-wheel motor  300 . For the purpose of illustration and discussion, the rotor  310  of the in-wheel motor  300  is shown to contain four poles corresponding to the four magnets  340 ,  342 ,  344 , and  346 . The rotor  310  magnetically couples the four poles so that there will be flux linkage for the magnetic flux generated by the windings L 1 -L 6 . The stator  304  contains six poles corresponding to the six windings L 1 -L 6  formed at an outer circumference of a mechanical support  302 .  FIG. 3  illustrates the magnetic flux  302  created when windings  1  and  4  of  FIG. 3  are switched on. As can be seen from the figure, the magnetic flux field  302  travels radially outward from the winding L 1  towards the rotor and then proceeds circumferentially around the rotor  310  to the winding L 4  on the opposite side of the stator  304 .  FIG. 3  is one non-limiting example configuration. 
       FIGS. 3-5  illustrate the driving means for driving the electromagnets  306  to cause the rotor  310  to rotate relative to the stator  304 . As shown in the circuit  500  of  FIG. 5 , each winding L 1 -L 6  of  FIG. 3  is controlled via a corresponding switch S 1 -S 6 . Although  FIG. 5  illustrates a one-to-one correspondence between the switches S 1 -S 6  and the windings L 1 -L 6 , such a relationship is not required, and a single switch S 1  may provide power to more than one winding L 1 -L 6 . 
     As set forth in  FIG. 5 , a control circuit  502 , such as a microcontroller, may be used to drive the switches S 1 -S 6  in a particular pattern. Alternately, a custom designed ASIC, FPGA, or other device could also be used to control the switching pattern of the circuit The switches S 1 -S 6  may be insulated gate bipolar transistors (IGBTs) or metal-oxide-semiconductor field-effect transistors (MOSFETs). Other switching devices could also be used. 
       FIG. 4  illustrates an example timing diagram for the switches S 1 -S 6  to drive the windings L 1 -L 6  of  FIGS. 3 and 5 . As shown in  FIG. 4 , switches S 1  and S 4  can be turned on substantially simultaneously in a first time period to energize windings L 1  and L 4 . Similarly, switches S 2  and S 5  can be energized substantially simultaneously in a second time period to energize windings L 2  and L 5 . Finally, switches S 3  and S 6  can be energized substantially simultaneously in a third period to energize windings L 3  and L 6 . This switching pattern can be repeatedly sequenced a number of times to drive the rotor  310  to rotate continuously relative to the stator  304 . Although  FIG. 4  illustrates square-wave pulses in the timing diagram, any other shape pulse could also be used, including for example, a sinusoidal pulse or a triangular pulse. 
     Where the relative rotor  310  and stator  304  are in the positions shown in  FIG. 3 , energizing windings L 3  and L 6  will cause the rotor  310  to move in the counter clock-wise position as the electromagnets  306  associated with windings L 3  and L 6  repel against magnets  310  and  312 , respectively. Alternately, given the same rotor  310  and stator  304  positions of  FIG. 3 , energizing windings L 2  and L 5  instead will cause the rotor  310  to move in the clockwise direction as the electromagnets  306  associated with windings L 2  and L 5  repel against magnets  310  and  312 , respectively. In practice, an optical or mechanical encoder may be used to provide a position indication of the rotor  310  to the control circuit. The control circuit could use the position indication in determining the proper timing of pulses to provide to the windings L 1 -L 6  to cause a desired clockwise or counter-clockwise movement of the rotor  310 . 
     A braking operation can also be implemented to cause an already rotating rotor  310  to slow down and/or stop. For example, we can assume that the rotor  310  of in-wheel motor  300  is already moving in a clockwise direction, and that  FIG. 3  shows a split second view of the relative rotor  310  and stator  304  positions. In this situation, the controller  502  can cause windings L 6  and L 3  of electromagnets  306  to be energized at the exact moment shown in  FIG. 3 . The energizing of windings L 6  and L 3  will cause the stator  304  to apply an electromagnet force against the magnets  342  and  340  in a rotational direction opposite the clockwise rotation of the rotor  310 . The remaining windings L 1 , L 2 , L 4 , and L 5  are driven in a similar manner as they approach corresponding magnets  340 - 346 . The driving pattern can then be repeated for each cycle of the rotor  310  around the stator  304 . This braking driving method will cause the rotor  310  to slow down and eventually stop. The amount of breaking will depend upon the pulse width of the switching pattern. 
     In an example embodiment, variation of the frequency of the pulses in the timing diagram of  FIG. 4  can be used to control the rotational speed of the rotor  310 . An increase in the frequency of the pulse trains applied to the windings  308  will cause a corresponding increase in speed of the rotor  310 . The duty cycle of the pulse trains applied to the windings  308  can be varied to control the torque applied to the rotor  310 . An increase in the duty cycle will cause a commensurate increase in the torque applied to the rotor  310 . 
       FIG. 6  illustrates a close-up view of the bearing  114  between the rotor  110  and the stator  102 . The bearing  114  allows relative axial rotation of the rotor  110  relative to the stator  102 . The bearing  114  may be a solid ring-shaped rubbing surface that, along with a lubricating material, allows the rotor  110  to slide relative to the stator  102 . Alternatively, and as shown in  FIG. 6 , the bearing  114  may be a rolling element bearing. Potential rolling element bearings include ball bearings, cylindrical roller bearings, tapered roller bearings, needle bearings, or spherical roller bearings. Other types of bearings can also be used, including, for example, liquid, gas, or magnetic bearings.  FIG. 6  illustrates an embodiment utilizing ball bearings. 
     The bearing  114  can support a radial load applied to the bearings from a vehicle attached to the wheel motor, and can support a thrust load applied during vehicle cornering. In the case of rolling element bearings, the bearings may be made from steel or stainless steel. Depending on the weight requirements of the application and bearings, other compositions such as polymers or ceramics could also be used. A lubricant such as grease or oil may be provided to decrease an amount of friction generated in the bearing  114 . Additionally, retainer rings or grooves may be provided on the rotor  110  or the stator  104  to maintain the bearings  114  in a proper position. 
       FIGS. 7 and 8  illustrate another embodiment of an in-wheel motor  700 .  FIG. 7  provides a front-view, while  FIG. 8  provides a rear-view of the same in-wheel motor  700 . The in-wheel motor  700  includes a stator projection ring  702  that extends orthogonally from a plane defined by the mechanical support  102 . As shown in  FIG. 7 , the stator projection ring  702  may be attached to portions of the stator  104 . The rotor  110  further includes a rotor projection ring  704  that extends orthogonally from a plane defined by the rotor  110  and surrounds the stator projection ring  702 . The in-wheel motor  700  includes a bearing  114  positioned between the stator projection ring  702  and the rotor projection ring  704 . By slightly offsetting the bearing  114  from the gap directly between the rotor  110  and the stator  104 , a bearing  114  can be utilized with reduced concerns about interfering with the magnetic interaction or coupling between the electromagnets  106  and the magnets  112 . 
     Although not shown in the Figures, a tire may be attached directly to an outer surface of the rotor  110 . The tire, for example, may be comprised of a rubber or rubber/composite compound, and may be inflated with air to maintain a particular tire pressure. The tire may include additional load-supporting sidewalls or plastic load-bearing inserts to allow the time to run safely for a limited range at a limited speed. In this embodiment, the rotor  110  may be formed so as to include flanges at outside edges of the outer surface that the tire may interface and bond width to secure the tire and rotor  110  together. 
     Alternately, although not shown, a cover may be provided circumferentially over the outside of the rotor  110  in order to protect the magnets  112 . Any additional support structure may be provided between the rotor  110  and the cover, such as a solid support, a plurality of spokes, or any other structure that can support a large weight load such as a locomotive. An outer surface of the cover may then directly contact a metal rail in operation so that rotation of the rotor  110  causes a locomotive or similar vehicle to move in a forward or reverse direction. In such an embodiment, the wheel may include a profile and flange on an inside portion to facilitate maintaining the wheel on the rail. In other example embodiments the rotor  110  may employ an additional mechanical support to a circumferential rim upon which a tire can be mounted. For example, the in-wheel motor may be implemented within a hub from which spokes extend radially outward to a rim with appropriate flanges to mount a tire. The hub includes rotor magnets (see in  FIG. 1  as  112 ) that are driven by the electromotive force of the stator magnets (see in  FIG. 1  as  106 ). The stator can be implemented integral with as a center axle. Bearings such as see in  FIG. 1  between the hub and the stator allow the hub to rotate around the stator. 
     Specifically, for example, a plurality of in-wheel motors  100  or  700  could be provided at predetermined vehicle locations. At rest, none of the switches S 1 -S 6  are energized. An encoder provided on the wheel or coupled to the wheel provides a position indication of the electromagnets  106  relative to the magnets  112  to a controller  502 . The controller  502  may then determine which electromagnets  106  are properly offset from corresponding magnets so as to avoid a driving deadlock situation. Once the controller  502  determines which electromagnets  106  to begin driving with, the controller  502  begins outputting a pulse pattern similar to that of  FIG. 4 . The pulse pattern is sequenced to avoid deadlock while causing rotation in a clockwise or counter-clockwise direction. The clockwise direction may correspond to a forward vehicle direction, while the counter-clockwise direction may correspond to a reverse vehicle direction, for example. 
     As noted earlier, a variation in the frequency of the switching pattern applied may be used to vary the speed of the rotor, while a variation in the pulse width of the switching pattern may be used to vary a torque applied to the rotor  110 . The switching pattern may continue at one or more frequencies until a braking operation is implemented. In order to brake, the controller  502  will apply a braking switching pattern to the switches that will result in an electromagnet force applied to the magnets  112  in a rotational direction opposite the current rotational direction of the rotor. The braking switching pattern may continue until the rotor  110  reaches a desired speed, or until the rotor reaches a complete stop. 
     In this manner, an in-wheel motor  900  can be provided that directly drives an outer tire or cover, eliminating transmission losses from a centralized engine, decreasing the overall weight of the vehicle, and increasing a range of an electric vehicle incorporating the in-wheel motor. Additionally, during vehicle braking, the in-wheel motor can provide regenerative power to pump energy back to a storage battery for use during a subsequent acceleration, further increasing the range of the electric vehicle incorporating the in-wheel motor. This also increases space efficiency since no separate centralized space is required for the motor. 
     The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds compositions or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. 
     With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 
     It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. 
     For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). 
     In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” 
     As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth. 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.