Abstract:
A method and apparatus in which a rotor ( 11 ) and a stator ( 17 ) define a radial air gap ( 20 ) for receiving AC flux and at least one DC excitation coil ( 23, 24 ) positioned near the stator end turn to produce DC flux in axial air gaps ( 21, 22 ) additive to the AC flux. Side magnets ( 16 ) and flux-guiding magnets ( 14 ) are provided as boundaries separating the side poles ( 12   a,    12   b ) of opposite polarity from other portions of the rotor ( 11 ) and from each other to define PM poles ( 12   a,    12   b ) for conveying the DC flux to or from the primary air gap ( 20 ) and for inhibiting flux from leaking from said pole portions prior to reaching the primary air gap ( 20 ). Side magnets ( 16 ), side poles ( 12   a  and  12   b ), flux-guiding magnets ( 14 ), ferromagnetic end plates ( 11   c ), non-magnetic end plates ( 12   c ), and ring bands ( 37 ) are optionally provided for performance improvement.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a Divisional Application of currently pending and allowed U.S. patent application Ser. No. 11/162,753 filed Sep. 21, 2005, entitled: “IMPROVEMENTS FOR HIGH STRENGTH UNDIFFUSED BRUSHLESS MACHINE AND METHOD,” which is a continuation-in-part of U.S. patent application Ser. No. 11/019,075 filed Dec. 21, 2004, which issued as U.S. Pat. No. 6,972,504 on Dec. 6, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 10/848,450 filed May 18, 2004, which issued as U.S. Pat. No. 6,989,619 on Jan. 24, 2006. Application Ser. No. 11/162,753 claims priority to U.S. Provisional Patent Application 60/675,419, filed Apr. 27, 2005 and is herein incorporated by reference in its entirety. This application is related to Hsu&#39;s previous U.S. Pat. Nos. 6,310,417 issued Oct. 30, 2001; 6,573,634 issued Jun. 3, 2003; and 6,700,297 issued Mar. 2, 2004, all herein incorporated by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    This invention was made with Government support under Contract No. DE-AC05000R22725 awarded to UT-Battelle, LLC, by the U.S. Department of Energy. The Government has certain rights in this invention. 
     
    
     TECHNICAL FIELD 
       [0003]    The field of the invention is brushless machines, including both AC and DC machines, including both motors and generators, and including permanent magnet (PM) machines and PM-reluctance machines. This invention specifically teaches flux guide technology for a High Strength Undiffused Brushless (HSUB) motor. 
       DESCRIPTION OF THE BACKGROUND ART 
       [0004]    There are three major types of brushless electric machines available for the electric vehicle (EV) and hybrid electric vehicle (HEV) drive systems. These are the induction machine, the PM machine, and the switched-reluctance machine. 
         [0005]    Permanent magnet (PM) machines with and without reluctance paths have been recognized for having a high power density characteristic. A PM rotor does not generate copper losses. One drawback of the PM motor for the above-mentioned application is that the air gap flux produced by the PM rotor is limited, and therefore, a sophisticated approach is required for high speed, field weakening operation. Another constraint is that inductance is low, which means that current ripple must be controlled. 
         [0006]    It is understood by those skilled in the art that a PM electric machine has the property of high efficiency and high power density. However, the air gap flux density of a PM machine is limited by the PM material, which is normally about 0.8 Teslas and below. A PM machine cannot operate at an air gap flux density as high as that of a switched reluctance machine. When the PM motor needs a weaker field with a reasonably good current waveform for high-speed operation, a sophisticated power electronics inverter is required. 
         [0007]    When considering a radial gap configuration for undiffused, high strength operation, several problems have to be overcome. It is desirable to provide a compact design with a shape similar to a conventional radial gap machine and to include laminated rotor-core structure. 
         [0008]    It would also be beneficial to further enhance the control of the field above that which is available with known PM rotor constructions. This would increase the motor torque. It is also an objective to accomplish this while retaining the compactness of the machine. 
         [0009]    The enhanced field weakening can reduce the field strength at high speed to lower the back EMF produced in the winding. Therefore, for a specified DC link voltage, the speed range of the machine can be increased over what it otherwise would be. This will meet the compactness objective and allow simplification of the drive system requirements. 
         [0010]    The permanent magnet (PM) motor is known to have higher power density among motors. However, the air-gap flux density of a PM motor is fixed due to the “permanent” nature of the magnet. The HSUB motor with the field enhancement and weakening capabilities can overcome the drawbacks of the PM motors. 
       SUMMARY OF THE INVENTION 
       [0011]    The electric machine may have at least one improved feature selected from the group consisting of at least one device selected from the group consisting of side magnets, side poles, flux-guiding magnets, ferromagnetic end plates, and ring bands. 
         [0012]    The electric machine may have at least one improved feature selected from the group consisting of flux-guiding magnets, side magnets, side poles, side ring, retaining rings, axial stationary flux path, and stationary excitation coils. Embodiments of the invention may incorporate a method and apparatus in which a rotor and a stator define a radial air gap for receiving AC flux. 
         [0013]    Embodiments of the invention provide increased power and torque without increasing the size of the machine. 
         [0014]    Embodiments of the invention are applicable to both AC and DC machines, and to both motors and generators. 
         [0015]    Embodiments of the invention are applicable to both PM machines with and without reluctance paths, respectively. The reluctance paths are known for producing reluctance torque components. 
         [0016]    Embodiments of the invention are applicable to both PM machines with and without stationary excitation field coils and stator axial flux paths. 
         [0017]    Embodiments of the invention provide a compact electric machine structure for application to electric or hybrid vehicles. 
         [0018]    Other objects and advantages of the invention, besides those discussed above, will be apparent to those of ordinary skill in the art from the description of the preferred embodiments which follows. In the description reference is made to the accompanying drawings, which form a part hereof, and which illustrate examples of the invention. Such examples however are not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0019]      FIG. 1  is a longitudinal section view of a HSUB machine with brushless excitation; 
           [0020]      FIGS. 2 and 3  are end views of the rotor incorporated in the assembly in  FIG. 1 ; 
           [0021]      FIGS. 2   a  and  3   a  are close-ups of the rotor face at the axial gaps; 
           [0022]      FIG. 4  is a longitudinal section view of a HSUB machine without brushless excitation; 
           [0023]      FIGS. 5 and 6  are end views of the rotor incorporated in the assembly in  FIG. 4 ; 
           [0024]      FIGS. 5   a  and  6   a  are close-ups of the rotor face at the axial gaps; 
           [0025]      FIG. 7  shows the flux-guide magnets on the rotor. As an option, the magnet strength on the left hand side can be chosen to be different from the right hand side. 
           [0026]      FIG. 8  is an end view of the rotor seen in  FIG. 7 ; 
           [0027]      FIG. 8   a  is an end view of a pole having multiple sets of flux-guide magnets for improving reluctance-torque production. 
           [0028]      FIGS. 9 and 10  show the rotor with and without both reluctance poles and additional side magnets, respectively; 
           [0029]      FIGS. 11 ,  12 , and  13  are another view of the improved features of the invention with the excitation coil flux shown. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    The principle of a high strength, undiffused brushless machine has been previously disclosed in the Hsu, U.S. Pat. No. 6,573,634, issued Jun. 3, 2003, Hsu, U.S. patent application Ser. No. 10/688,586 filed Sep. 23, 2003, and Hsu U.S. patent application Ser. Appl. No. 10/848,450 filed May 18, 2004, the disclosures of which are hereby incorporated by reference. 
         [0031]    For a conventional PM machine the air-gap flux density is about 0.6 to 0.8 Teslas and cannot be weakened without the aid of some sophisticated power electronics. Both the stationary excitation coil and the PM material in the rotor maximize rotor flux in the PM machines of the embodiments of the present invention. These embodiments can produce two to three times the air gap flux density of a conventional PM machine. Because the PM torque produced by an electric machine is directly proportional to the air gap PM flux density, a higher torque, more powerful machine is provided with only small additions to size and weight. 
         [0032]      FIG. 1  shows a longitudinal section view of a radial gap, high strength undiffused machine  10  with eight side poles  12   a,    12   b  in a rotor assembly  11 .  FIGS. 2 and 3  each show the eight side poles  12   a  and  12   b  attached to the sides of the rotor core in an area bounded by eight sets of flux-guiding magnets  14  that consist of three pieces of magnets for guiding flux towards the radial air gap  20  for the sample eight-pole machine. The eight side magnets  16  help to prevent leakage flux at the rotor sides. Optionally, reluctance side poles  15  are provided by the portions of the rotor positioned in between the side magnet  16  and side pole  12   a  and  12   b  and between the flux-guiding magnets  14  without contacting the flux-guiding magnets  14 . The reluctance side poles  15  allow the flux produced by a stator  17  to go through these reluctance side poles  15  easier than the path going through the side poles  12   a  and  12   b.    
         [0033]    The rotor assembly  11  is preferably made as described in the disclosures cited above, namely, the rotor has a hub  11   a  and a plurality of laminations  11   b  of ferromagnetic material are mounted and stacked on the hub  11   a  and clamped by non-magnetic end plates  12   c.  The rotor laminations  11   b  and ferromagnetic end plates  11   c  have keyed projections  11   d  for insertion in keyways in the rotor hub  11   a.  The ferromagnetic end plates  11   c  can be made of solid mild steel or stacked laminations. 
         [0034]    The side poles  12   a,    12   b  are made of ferromagnetic material. The flux-guiding magnets  14  can be pre-formed pieces or the injected type. Between pieces of flux-guiding magnets  14 , an epoxy material can be used to fill gaps. Side magnets  16  are separate pieces attached to the ends of the rotor assembly  11 . Bolts (not shown) are used to hold the side poles  12   a,    12   b  and ferromagnetic end plates  11   c  in position. Ring band  37  can hold the side poles  12   a,    12   b,  side magnets  16 , and ferromagnetic end plate  11   c  in place to withstand the centrifugal force. 
         [0035]    The machine  10  optionally has brushless excitation as shown in  FIGS. 1 and 4 . Brushless excitation of  FIG. 1  is provided by stationary coils  23  and  24  and stationary flux collectors  25  and  26 . No brushless excitation is used in  FIG. 4  wherein the machine  10  is absent stationary coils and stationary flux collectors. 
         [0036]    The rotor assembly  11  rotates with a main drive shaft  19  around an axis of rotation  19   a.  The stator  17  is disposed around the rotor  11  and has a laminated core  17   a  and windings  17   b  as seen in a conventional AC machine. The rotor assembly  11  is separated from the stator  17  by a radial air gap  20 , which is also referred to herein as the primary air gap. AC flux is produced in this air gap  20  by the stator field. With brushless excitation, the rotor assembly  11  is separated from the stationary flux collectors  25  and  26  by axial air gaps  21  and  22 , respectively. These air gaps  21 ,  22  are oriented perpendicular to the axis  19   a  of the rotor  11 . DC flux will be produced in these air gaps  21 ,  22  by excitation coils  23  and  24 . Stationary flux collectors  25  and  26  are disposed at the axial air gaps  21 ,  22 . The laminated option of stationary flux collector can further smooth the DC flux component and reduce the possible occurrence of eddy currents. 
         [0037]    The drive shaft  19  is supported by bearings  31  and  32 . A short internal shaft  30  is also coupled to the rotor  11 . A shaft encoder  33  and a pump  34  for lubricant for the motor  10  are situated inside a passageway  35  through the hollow center of the excitation coil  24 . A housing cover  36  closes the passageway  33 . 
         [0038]    Referring to  FIG. 2 , the DC flux produced by the excitation coils  23 ,  24  is conducted into the rotor from one set of the ferromagnetic side poles  12   a  attached to the N polarity of the rotor, and then turns to flow radially outward across the main air gap  20  into the stator core  17   a,  then loops and returns radially inward and is conducted axially outward through adjacent side poles  12   b  attached to the S polarity at the other end of the rotor  11  ( FIG. 3 ). The DC flux produced by the excitation coils does not pass through the reluctance side poles  15 . The DC flux return path  38  (labeled in  FIG. 11 ) goes through the frame that is made of magnetically conducting material. 
         [0039]    Referring to  FIGS. 2 and 3 , the flux-guiding magnets  14  together with the excitation current going through the excitation coils  23  and  24  produce the north (N) and south (S) poles on the exterior of rotor  11  that faces the stator  17  and the radial air gap  20 . This rotor flux in the radial air gap  20  can be either enhanced or weakened according to the polarity of the DC excitation in the excitation assemblies  23 ,  24  that face the ends the rotor  11 . Subsequently, the radial air gap  20  receives the rotor flux from the rotor  11 , which interacts with the primary flux induced by the stator windings  17   b  to produce a torque. 
         [0040]      FIGS. 7 and 8  show the flux-guiding magnets  14  inside the rotor lamination  11   b.  As an option, a strong flux guiding magnet set  14   a  and a weak magnet  14   b  can be chosen. 
         [0041]      FIG. 8   a  shows a rotor assembly  11 ′ illustrating that the flux-guiding magnets  14  can be modified to consist of multiple sets of magnets for each pole disposed on multiple grooves to increase the reluctance torque value. 
         [0042]      FIGS. 9 and 10  show the rotor with and without reluctance side poles  15  installed, respectively. 
         [0043]      FIGS. 11 ,  12  and  13  illustrate an embodiment of the improvements of the current invention. 
         [0044]    The functions of each optional improvement are described as follows. The flux-guiding magnets  14  and side magnets  16  are used to conduct the axial fluxes and to block the unwanted axial leakage flux during field enhancement. The flux-guiding magnets  14  are typically thin with respect to the width of the grooves in which they are situated. A thinner magnet can reduce the cost of permanent magnets. During field enhancement the higher air-gap flux density is produced by the brushless field excitation. Therefore, a weaker and thinner PM can do the job as part of the flux-guiding barriers to discourage the flux going across the grooves. The ferromagnetic end plate  11   c  smoothes the axial flux and produces a return path for the side magnets  16 . The ring band  37  prevents the side poles, side magnets and end pieces from flying apart due to the centrifugal force. 
         [0045]    The HSUB technology is for electric vehicle and hybrid electric vehicle applications. However, the HSUB technology certainly can be used for other applications where the use of electricity to produce torque and motion is involved. 
         [0046]    The invention is applicable to both AC synchronous and DC brushless machines and to both motors and generators. 
         [0047]    This has been a description of the preferred embodiments of the invention. The present invention is intended to encompass additional embodiments including modifications to the details described above which would nevertheless come within the scope of the following claims.