Patent Publication Number: US-10312783-B2

Title: Variable flux bridge for rotor an electric machine

Description:
TECHNICAL FIELD 
     The present disclosure relates to an electric machine assembly of an electrified vehicle. 
     BACKGROUND 
     Extended drive range technology for electrified vehicles, such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug in hybrid vehicles (PHEVs), is continuously improving. Achieving these increased ranges, however, often requires traction batteries and electric machines to have higher power outputs and associated thermal management systems with increased capacities in comparison to previous BEVs and PHEVs. Improving efficiency between electric machine stator cores and rotors may increase power outputs of the electric machine. 
     SUMMARY 
     An electric machine assembly for an electrified vehicle includes a stator core, a rotor, a first pair of magnets, a second pair of magnets, and a variable flux magnet. The stator core defines a cavity. The rotor is disposed within the cavity for rotation and includes a bridge. Each of the first pair of magnets is mounted to the rotor and spaced from one another on either side of a first D-axis. Each of the second pair of magnets is mounted to the rotor and spaced from one another on either side of a second D-axis. The first D-axis and the second D-axis are spaced from one another on either side of a Q-axis. The variable flux magnet is embedded in the bridge and located on the rotor to influence current associated with the Q-axis to control torque output of the rotor, and to pulse D-axis current to control a magnetization of the bridge. The magnets of the first pair of magnets or the second pair of magnets may be arranged with one another to define an inverted V shape. The assembly may further include a first side flux barrier disposed on a first side of the variable flux magnet and a second side flux barrier disposed on a second side of the variable flux magnet. The side flux barriers may be arranged with the variable flux magnet to prevent vertical current or flux associated with the Q-axis from influencing magnetization of the variable flux magnet. The first side flux barrier and the second side flux barrier may each be located to influence magnetic flux to flow in a substantially horizontal path through the variable flux magnet. The variable flux magnet may be one of AlNiCo, ferrite, and a low energy rare-earth metal. The variable flux magnet may be arranged with the first pair of magnets and the second pair of magnets such that magnetic flux associated with the Q-axis is diverted about the variable flux magnet to control the rotor torque output. 
     An electric machine assembly for an electrified vehicle includes a stator core, a rotor, a first pair of magnets, a second pair of magnets, and a trapezoidal-shaped variable flux magnet. The stator core defines a cavity. The rotor is disposed within the cavity and includes a bridge. The first pair of magnets are arranged with one another to generate current along a first D-axis when the rotor is rotating and the stator core is activated. The second pair of magnets are arranged with one another to generate current along a second D-axis when the rotor is rotating and the stator core is activated. The trapezoidal-shaped variable flux magnet is embedded in the bridge and arranged with the first and second pairs of magnets such that current associated with a Q-axis bisecting the variable flux magnet travels in a substantially horizontal path through the variable flux magnet. The variable flux magnet includes a first side and a second side. The first side is closer to an outer surface of the rotor and has a shorter length than a length of the second side. The trapezoidal shape of the variable flux magnet may create a first path and a second path thicker than the first path to influence magnetic flux to travel along the substantially horizontal path. The assembly may further include a first side flux barrier and a second side flux barrier each disposed on opposing sides of the variable flux magnet to block or minimize magnetic flux traveling in a substantially vertical flow path. 
     An electric machine assembly includes a rotor, a variable flux magnet, and first and second magnets. The rotor is disposed within a stator core and includes a bridge. The variable flux magnet is embedded in the bridge. The first and second magnets are arranged to define a D-axis therebetween and to define an inverted slope to focus magnetic flux associated with the D-axis into the variable flux magnet and increase a current effect associated with the D-axis on magnetization of the variable flux magnet. The assembly may further include a tangent axis defined by an outer surface of the rotor and an offset axis spaced parallel from the tangent axis. One of the magnets may define an edge axis and an angle of the edge axis relative to the offset axis may be selected to affect an amount of magnetic flux associated with the D-axis transferred into the variable flux magnet to influence a magnetization of the variable flux magnet. The angle of the edge axis relative to the offset axis may be between twenty-five and thirty-five degrees. The angle of the edge axis relative to the offset axis may be approximately thirty degrees. The first magnet and the second magnet may be arranged with one another to form an inverted V. The assembly may further include a first side flux barrier and a second side flux barrier each disposed on one of opposing sides of the variable flux magnet to retain flux of the variable flux magnet therebetween. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating an example of an electrified vehicle. 
         FIG. 2  is a perspective, exploded view of an example of a portion of an electric machine. 
         FIG. 3  is a graph showing an example of a torque speed curve for an electric machine. 
         FIG. 4  is a partial front view, in cross-section, of a portion of an example of a rotor for an electric machine. 
         FIG. 5  is a graph showing another example of a torque speed curve for an electric machine. 
         FIG. 6  is a schematic diagram showing an example of a relationship between a spring and sliding bridge of a rotor. 
         FIG. 7A  is a partial front view, in cross-section, of a portion of an example of a rotor and stator for an electric machine showing a bridge in a first position. 
         FIG. 7B  is a partial front view, in cross-section, of the portion of the example of the rotor and the stator for an electric machine of  FIG. 5  showing the bridge in a second position. 
         FIG. 7C  is a partial front view, in cross-section, of the portion of the example of the rotor and the stator for an electric machine of  FIG. 5  showing the bridge in a third position. 
         FIG. 8  is a partial front view, in cross-section, of a portion of another example of a rotor for an electric machine showing orientation axes and magnetic flux paths for various electric machine components. 
         FIG. 9  is a partial front view, in cross-section, of a portion of another example of a rotor for an electric machine showing an example of magnetic flux flow paths influenced by various electric machine components. 
         FIG. 10  is a partial front view, in cross-section, of a portion of yet another example of a rotor for an electric machine showing another example of magnetic flux flow paths influenced by various electric machine components. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present disclosure. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
       FIG. 1  is a schematic diagram illustrating an example of an electrified vehicle. In this example, the electrified vehicle is a PHEV referred to as a vehicle  12  herein. The vehicle  12  may include one or more electric machines  14  mechanically connected to a hybrid transmission  16 . Each of the electric machines  14  may be capable of operating as a motor or a generator. In addition, the hybrid transmission  16  is mechanically connected to an engine  18 . The hybrid transmission  16  is also mechanically connected to a drive shaft  20  that is mechanically connected to wheels  22 . The electric machines  14  can provide propulsion and deceleration capability when the engine  18  is turned on or off. The electric machines  14  may also operate as generators and provide fuel economy benefits by recovering energy that would normally be lost as heat in the friction braking system. The electric machines  14  may also provide reduced pollutant emissions since the vehicle  12  may be operated in electric mode under certain conditions. 
     A traction battery  24  stores energy that can be used by the electric machines  14 . The traction battery  24  typically provides a high voltage DC output from one or more battery cell arrays, sometimes referred to as battery cell stacks, within the traction battery  24 . The battery cell arrays may include one or more battery cells. The traction battery  24  is electrically connected to one or more power electronics modules  26  through one or more contactors (not shown). The one or more contactors isolate the traction battery  24  from other components when opened and connects the traction battery  24  to other components when closed. The power electronics module  26  is also electrically connected to the electric machines  14  and provides the ability to bi-directionally transfer electrical energy between the traction battery  24  and the electric machines  14 . For example, a typical traction battery  24  may provide a DC voltage while the electric machines  14  may require a three-phase AC voltage to function. The power electronics module  26  may convert the DC voltage to a three-phase AC voltage as required by the electric machines  14 . In a regenerative mode, the power electronics module  26  may convert the three-phase AC voltage from the electric machines  14  acting as generators to the DC voltage required by the traction battery  24 . Portions of the description herein are equally applicable to a pure electric vehicle. For a pure electric vehicle, the hybrid transmission  16  may be a gear box connected to an electric machine  14  and the engine  18  may not be present. 
     In addition to providing energy for propulsion, the traction battery  24  may provide energy for other vehicle electrical systems. A typical system may include a DC/DC converter module  28  that converts the high voltage DC output of the traction battery  24  to a low voltage DC supply that is compatible with other vehicle loads. Other high-voltage loads, such as compressors and electric heaters, may be connected directly to the high-voltage without the use of a DC/DC converter module  28 . In a typical vehicle, the low-voltage systems are electrically connected to an auxiliary battery  30  (e.g., a twelve-volt battery). 
     A battery electrical control module (BECM)  33  may be in communication with the traction battery  24 . The BECM  33  may act as a controller for the traction battery  24  and may also include an electronic monitoring system that manages temperature and charge state of each battery cell of the traction battery  24 . The traction battery  24  may have a temperature sensor  31  such as a thermistor or other temperature gauge. The temperature sensor  31  may be in communication with the BECM  33  to provide temperature data regarding the traction battery  24 . 
     The vehicle  12  may be recharged by an external power source  36  such as an electrical outlet. The external power source  36  may be electrically connected to an electric vehicle supply equipment (EVSE)  38 . The EVSE  38  may provide circuitry and controls to regulate and manage the transfer of electrical energy between the power source  36  and the vehicle  12 . The external power source  36  may provide DC or AC electric power to the EVSE  38 . The EVSE  38  may have a charge connector  40  for plugging into a charge port  34  of the vehicle  12 . The charge port  34  may be any type of port configured to transfer power from the EVSE  38  to the vehicle  12 . The charge port  34  may be electrically connected to a charger or on-board power conversion module  32 . The power conversion module  32  may condition the power supplied from the EVSE  38  to provide the proper voltage and current levels to the traction battery  24 . The power conversion module  32  may interface with the EVSE  38  to coordinate the delivery of power to the vehicle  12 . The charge connector  40  may have pins that mate with corresponding recesses of the charge port  34 . 
     The various components discussed above may have one or more associated controllers to control and monitor the operation of the components. The controllers may communicate via a serial bus (e.g., a controller area network (CAN)) or via discrete conductors. 
     The battery cells of the traction battery  24 , such as a prismatic or pouch-type cell, may include electrochemical elements that convert stored chemical energy to electrical energy. Prismatic cells or pouch-type cells may include a housing, a positive electrode (cathode) and a negative electrode (anode). An electrolyte may allow ions to move between the anode and cathode during a discharge operation, and then return during a recharge operation. Terminals may allow current to flow out of the battery cells for use by the vehicle. When positioned in an array with multiple battery cells, the terminals of each battery cell may be aligned with opposing terminals (positive and negative) adjacent to one another and a busbar may assist in facilitating a series connection between the multiple battery cells. The battery cells may also be arranged in parallel such that similar terminals (positive and positive or negative and negative) are adjacent to one another. 
       FIG. 2  is a partially exploded view illustrating an example of portions of an electric machine for an electrified vehicle, referred to generally as an electric machine  100  herein. The electric machine may include a stator core  102  and a rotor  106 . As mentioned above, electrified vehicles may include two electric machines. One of the electric machines may function primarily as a motor and the other may function primarily as a generator. The motor may operate to convert electricity to mechanical power and the generator may operate to convert mechanical power to electricity. The stator core  102  may define an inner surface  108  and a cavity  110 . The rotor  106  may be sized for disposal and operation within the cavity  110 . A shaft  112  may be operably connected to the rotor  106  and be coupled to other vehicle components to transfer mechanical power therefrom. 
     Windings  120  may be disposed within the cavity  110  of the stator core  102 . In an electric machine motor example, current may be fed to the windings  120  to obtain a rotational force on the rotor  106 . In an electric machine generator example, current generated in the windings  120  by a rotation of the rotor  106  may be used to power vehicle components. Portions of the windings  120 , such as end windings  126 , may protrude from the cavity  110 . During operation of the electric machine  100 , heat may be generated along the windings  120  and end windings  126 . The rotor  106  may include magnets such that rotation of the rotor  106  in cooperation with an electric current running through the end windings  126  generates one or more magnetic fields. For example, electric current running through the end windings  126  generates a rotating magnetic field. Magnets of the rotor  106  will magnetize and rotate with rotating magnetic field to rotate the shaft  112  for mechanical power. 
       FIG. 3  shows a graph illustrating an example of a torque speed curve for an electric machine, generally referred to as a graph  200  herein. An X-axis  204  represents a speed of rotor rotation and a Y-axis  206  represents torque for electric machine operation. Torque speed curve  210  represents a typical torque output versus rotor speed for an electric machine. Region  212  represents an area of a high torque performance requirement and region  214  represents an area of low torque drive cycle points. Electric machine function in automotive traction applications may require high torque for performance relative to an amount of torque required to operate through much of EPA efficiency cycles. Permanent magnet motors are often used due to their high efficiency provided by “free” rotor magnetic fields associated with permanent magnets. However, one drawback is that this free rotor magnetic field is always “on” and stator core loss in the electric machine is a function of the magnetic field. For high torque points, a large rotor field is needed to product a large amount of torque with low current. However, for low or zero torque points, a large rotor field may create high stator core loss. Consequently, for electric machines that require high maximum torque and low drive cycle torque, the constant permanent magnet rotor field is typically only optimized for one of the desired conditions. 
       FIG. 4  is a partial cross-sectional view illustrating an example of a portion of a rotor of an electric machine, referred to as a rotor  230  herein. The electric machine may operate with an electrified vehicle or a vehicle including only an internal combustion engine. The rotor  230  includes an assembly to create a permanent magnet machine with variable rotor flux by using a sliding bridge to create a rotor flux field that varies with rotor  230  rotational speed and a position of a bridge. Creating variable rotor flux provides both high and low torque outputs to accommodate varied torque demands in a vehicle drive cycle. With variable rotor flux, a torque output of a shaft coupled to the rotor  230  may be tuned based on a speed of rotation of the rotor  230 . For example, the rotor  230  may include a pair of first magnets  232 , a pair of second magnets  234 , and a channel  236  disposed between each of the pairs of magnets. Each of the magnets may be, for example, a rare-earth magnet such as a neodymium magnet. The channel  236  may be spaced substantially equidistant from the magnets. A first end of the channel  236  may be spaced from an outer surface of the rotor  230  a distance based on predetermined stress operating parameters of the rotor  230 . A bridge  238  may be disposed within the channel  236  for translation between at least first and second positions. For example, a centrifugal force created by rotation of the rotor  230  may influence movement of the bridge  238  within the channel  236 . The bridge  238  may be of a soft ferromagnetic material having a high susceptibility to magnetism and high permeability characteristics. Examples of materials for the bridge  238  include silicone steel, iron, cobalt, and ferrite. 
     By predictably controlling a position of the bridge  238  within the channel  236 , shunt flux path thickness may be changed depending on positioning of the bridge  238 . A first non-magnetic guide  242  and a second non-magnetic guide  244  may each be disposed on opposing sides of the channel  236  at or near a substantially central channel region. The first non-magnetic guide  242  and the second non-magnetic guide  244  may be of a material having a low friction coefficient and non-magnetic characteristics, such as a polymer. For example, the low friction coefficient may assist in influencing an easier translation of the bridge  238  in comparison to a material of the rotor  230  or other higher friction coefficient materials. The bridge  238  may be positioned in an at rest region  246  when the rotor  230  is at rest. The bridge  238  may slide through a transitional region to an active shunt flux region  248  when the rotor  230  is rotating due to the centrifugal force. The bridge  238  is in a full shunt region when positioned at or near an upper wall of the channel  236 . The bridge  238  may be disposed within the channel  236  such that air pockets are defined on either side of the bridge  238 . The air pockets may operate as flux barriers to block rotor flux leakage until the bridge  238  is in the active shunt flux region  248 . 
     The first non-magnetic guide  242  and the second non-magnetic guide  244  may assist in blocking magnetic flux leakage traveling in a direction from the bridge  238  toward one of the pairs of magnets, represented by arrows  245 . A shape of each of the first non-magnetic guide  242  and the second non-magnetic guide  244  may vary based on an angle or orientation of the magnets mounted to the rotor  230  and located adjacent thereto. For example, each of the non-magnetic guides may include a guide edge substantially parallel with a magnet edge of one of the adjacent magnets of the pair of first magnets  232  or the pair of second magnets  234 . In this example, each of the non-magnetic guides are shown having a substantially elongated triangular shape, however it is contemplated that the non-magnetic guides may have other shapes, such as a substantially rectangular shape in an embodiment in which adjacent magnets are oriented to define an edge or plane parallel with a rectangular side of the non-magnetic guides. 
     Optionally, a spring  250  may be disposed within the channel  236  to bias movement of the bridge  238  in a predictable fashion. For example, the spring  250  may be oriented within the channel  236  to predictably influence centripetal force to oppose the centrifugal force acting on the bridge  238  when the rotor  230  is rotating as mentioned above. Additionally, the spring  250  may operate to retain the bridge  238  in the at rest region  246  when the rotor  230  is not rotating. The spring  250  may be secured to one end of the bridge  238  and to an interior surface of the channel  236 . The spring  250  may operate to predictably influence the bridge  238  to be located within the active shunt flux region  248  under certain conditions such as a speed at which the rotor  230  is rotating. The bias of the spring  250  may be tuned based on a size of the rotor, a centrifugal force range based on operating conditions of the rotor  230 , and motor torque speed specifications. 
       FIGS. 5 and 6  illustrate an example of a mechanical relationship between a spring, bridge, and rotor such as the spring  250 , the bridge  238 , and the rotor  230 . In  FIG. 5 , an X-axis  251  represents revolutions per minute (RPM) and a Y-axis  252  represents torque. Line  253  represents a torque speed curve. Rotational speed of the rotor is represented at line  254  for RPM1, at line  255  for RPM2, and at line  256  for RPM3. As mentioned above, centrifugal force (represented in  FIG. 6  by force arrow F c ) created by rotation of the rotor  230  may influence movement of the bridge  238  within the channel  236 . The bridge  238  may be in the rest position when the rotor  230  is rotating at RPM1. The bridge  238  may be in between the transition region and the active shunt region when the rotor  230  is rotating at RPM2. The bridge  238  may be in a full shunt position when the rotor  230  is rotating at RPM3. 
     To influence positioning of the bridge  238  within the channel  236 , a spring constant of the spring  250  may be based on a mass of the bridge  238  and desired movement of the bridge  238 .  FIG. 6  shows a schematic representation of the rotor  230 , the bridge  238 , and the spring  250 . Line  257  at X1 may correspond to the at rest position of the bridge  238 . Line  258  at X2 may correspond to a bridge  238  position between the transitional region and the active shunt region. Line  259  at X3 may correspond to the full shunt position of the bridge  238 . 
     A force equation for the spring  250  may be represented by
 
 F   s   =kx.  
 
     A force equation for the sliding bridge  238  mass under acceleration may be represented by
 
 F   c   =mrω   2   =mr πRPM 2 /30.
 
     An equation of the system may be represented by 
     
       
         
           
             k 
             = 
             
               
                 
                   
                     mr 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     π 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       RPM 
                       2 
                     
                   
                   
                     30 
                     ⁢ 
                     x 
                   
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 or 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 x 
               
               = 
               
                 
                   
                     mr 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     π 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       RPM 
                       2 
                     
                   
                   
                     30 
                     ⁢ 
                     k 
                   
                 
                 . 
               
             
           
         
       
     
     To identify a spring constant of the spring  250  and deformation, desired speeds for transitions RPM1, RPM2, and RPM3 are defined based on performance requirements of the rotor  230 . X1 may then be selected and k may be solved for at RPM1. Using k, X2 may be solved for at RPM2 and X3 may be solved for at RPM3. 
       FIGS. 7A through 7C  illustrate examples of positions for the bridge  238  to generate different magnetic flux paths relative to a stator core  260  having end windings  262 . Magnetic shunt flux generated by one of the pair of first magnets  232  and one of the pair of second magnets  234  adjacent to one another is represented by flow path  261 . Magnetic flux generated by the stator core  260  is represented by flow path  263 . In  FIG. 7A , the bridge  238  is shown not engaged with the flow path  261  and in the at rest position in the rest region  246 . In this position, the bridge  238  promotes a flow of magnetic flux to the stator core  260 . In  FIG. 7B , the bridge  238  is shown partially engaged with the flow path  261  in the transition region en route to the active shunt flux region  248 . In  FIG. 7C , the bridge  238  is shown engaged with the flow path  261  and in the active shunt position in the active shunt flux region  248 . In this position, the bridge  238  promotes magnetic flux flow generated by the pair of first magnets  232  and the pair of second magnets  234  to minimize induced voltage and magnetic loss by retaining magnetic flux within the rotor  230  while minimizing interaction with the end windings  262 . 
       FIGS. 8 through 10  are partial cross-sectional views illustrating another example of a rotor, generally referred to as a rotor  300  herein. The rotor  300  may operate within an electric machine of an electrified vehicle or a vehicle having only an internal combustion engine. The rotor  300  includes an assembly to create a permanent magnet machine with variable rotor flux. For example, the rotor  300  may include a pair of first magnets  304 , a pair of second magnets  306 , and a variable flux magnet  310  embedded in a bridge  312 . Each of the pair of first magnets  304  and the pair of second magnets  306  may be, for example, a rare-earth magnet such as a neodymium magnet. The variable flux magnet  310  may be, for example, a magnet having lower coercive force properties such as AlNiCo, ferrite, or a low energy rare-earth metal as further described herein. Each of the pair of first magnets  304  may be arranged with one another to form an inverted V. Each of the pair of second magnets  306  may be arranged with one another to form an inverted V. Spaces  316  may be defined by the rotor  300  on either side of each of the pair of first magnets  304  and spaces  318  may be defined by the rotor  300  on either side of each of the magnets the pair of second magnets  306 . The spaces  316  and the spaces  318  provide a structure to assist in orienting the pair of first magnets  304  and the pair of second magnets  306  relative to the variable flux magnet  310 . 
     Magnetic shunt flux generated by one of the pair of first magnets  304  and one of the pair of second magnets  306  adjacent to one another is represented by flow path  315 . Magnetic flux generated by a stator core (not shown) is represented by flow path  317 . 
     Embedding the variable flux magnet  310  within the bridge  312  assists in shunting magnetic flux when high torque is not needed by preventing excess magnetic flux from reaching the adjacent stator core. Depending on a magnetization state of the variable flux magnet  310 , flux from a primary path along a Q-axis from the rotor  300  to a stator may be added, subtracted, or ignored. The variable flux magnet  310  may have characteristics to resist magnetic flux from the primary path while also being controlled with a reasonable D-axis current. For example, AlNiCo is a material which may be used due to lower coercive force characteristics and a higher insensitivity to temperatures. Ferrite or a weaker/thinner rare earth grade material may also be used. 
     The variable flux magnet  310  may be wedge-shaped to assist in controlling magnetic flux when the rotor  300  is in operation. For example, the variable flux magnet  310  may have a trapezoidal shape in which an outer side  319  has a length less than an inner side  321  as shown in  FIG. 8 . It is also contemplated that the outer side  319  may have a length greater than the inner side  321  in another assembly example. This trapezoidal shape may assist in providing magnetic flux paths of varied length to control magnetization characteristics as system efficiency may be improved with increased control of interchanging north and south poles of the variable flux magnet  310 . For example, thinner paths may require a smaller field to magnetize or demagnetize the variable flux magnet  310  to create a smaller D-axis current. Thicker paths may require a larger field to magnetize or demagnetize the variable flux magnet  310  to create a larger D-axis current. The D-axis current may be pulsed to assist in controlling magnetization of the bridge  312 . For example, the D-axis current may be pulsed at a transition between a low torque output to a high torque output (or vice versa) to control bridge magnetization appropriate to an amount of magnetic flux shunting required. 
     A first D-axis  324  may be defined between the pair of first magnets  304  and spaced equidistant from edges of each of the adjacent spaces  316 . A second D-axis  326  may be defined between the pair of first magnets  304  and spaced equidistant from edges of each of adjacent spaces  318 . Each of the first D-axis  324  and the second D-axis  326  represent a centerline of a magnetic pole. For example, the pair of first magnets  304  may represent a south pole and the pair of second magnets  306  may represent a north pole. It is contemplated that similar D-axes would be dispersed throughout the rotor  300  in similar locations relative to other adjacent pairs of magnets. 
     A Q-axis  332  may be defined between one of the pair of first magnets  304  and one of the pair of second magnets  306 , spaced equidistant from edges of the space  316  and the space  318  adjacent one another, and disposed between the first D-axis  324  and the second D-axis  326 . It is contemplated that similar Q-axes would be dispersed throughout the rotor  300  in similar locations relative to other adjacent magnets. The variable flux magnet  310  may be bisected by the Q-axis  332  or may be offset in either direction from the Q-axis  332 . Current flowing along the Q-axis  332  may assist in controlling torque output of the rotor  300 . 
     The first D-axis  324  may be perpendicular to a first tangential axis  340 . The first tangential axis  340  may represent a tangent of an outer surface of the rotor  300 . The second D-axis may be perpendicular to a second tangential axis  342 . The second tangential axis  342  may represent another tangent of the outer surface of the rotor  300 . The Q-axis may be perpendicular to a third tangential axis  344 . The third tangential axis  344  may represent yet another tangent of the outer surface of the rotor  300 . 
     A first offset axis  350  may be spaced parallel from the first tangential axis  340  and perpendicular to the first D-axis  324 . The first offset axis  350  may intersect with a corner of each of the pair of first magnets  304 . Each of the pair of first magnets  304  may include an edge  352  defining a first edge axis  354 . Each of the first edge axes  354  may be arranged relative to the first offset axis  350  at an angle between zero and ninety degrees, represented by angle  358 . In one example, each of the first edge axes  354  is arranged at a thirty-degree angle relative to the first offset axis  350 . 
     A second offset axis  360  may be spaced parallel from the second tangential axis  342  and perpendicular to the second D-axis  326 . The second offset axis  360  may intersect with a corner of each of the pair of second magnets  306 . Each of the pair of second magnets  306  may include an edge  362  defining a second edge axis  364 . Each of the second edge axes  364  may be arranged relative to the second offset axis  360  at an angle between zero and ninety degrees, represented by angle  368 . In one example, each of the second edge axes  364  is arranged at a thirty-degree angle relative to the second offset axis  360 . 
     Each of the inverted V shapes defined by the pair of first magnets  304  and the pair of second magnets  306  assist in focusing D-axis flux into the variable flux magnet  310  to allow a magnification of the D-axis current effect on magnetization. In  FIG. 9 , each of the pair of first magnets  304  and the pair of second magnets  306  are arranged to not interfere with magnetic flux generated by the stator core and represented by flow path  365 . This arrangement assists in directing the flow path  365  into the variable flux magnet  310 . 
     Various orientations of each of the pair of first magnets  304  and the pair of second magnets  306  are available to arrange the magnets to assist in directing the flow path  365  into the variable flux magnet  310 . For example, an upper outer corner  370  of one of the pair of first magnets  304  and an upper outer corner  372  of one of the pair of second magnets  306  may be spaced from the outer surface of the rotor  300  at a distance based on predetermined stress operating parameters of the rotor  300 . An upper inner corner  374  of one of the pair of first magnets  304  and an upper inner corner  376  of one of the pair of second magnets  306  may be spaced from the outer surface of the rotor  300  at a distance based on predetermined stress operating parameters of the rotor  300 . 
     Each of a first side flux barrier  380  and a second side flux barrier  382  may be mounted to the rotor  300  on opposing sides of the variable flux magnet  310 . The first side flux barrier  380  and the second side flux barrier  382  may assist in preventing Q-axis current or flux from influencing a magnetization state of the variable flux magnet  310 . For example, the first side flux barrier  380  and the second side flux barrier  382  may influence magnetic flux flowing through the variable flux magnet  310  to be substantially horizontal (as represented by flow path  390  in  FIG. 10 ) in comparison to substantially vertical (as represented by flow paths  392  in  FIG. 10 ). The first side flux barrier  380  and the second side flux barrier  382  may also provide a measure of separation from D-axis flux from the stator and D-axis flux from the first pair of first magnets  304  and the second pair of second magnets  306  to assist in facilitating better magnetization control of the variable flux magnet  310 . While in this example the first side flux barrier  380  and the second side flux barrier  382  are shown having three barriers of a substantially straight shape, it is contemplated that a greater number of barriers may be utilized having a curved shape. 
     The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments may be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.