Abstract:
A single phase, rotary electromagnetic actuator comprising first and second stator assemblies, located in oppositely facing spaced apart positions along a common central axis, permits a magnetized disc magnet rotor to rotate about the common axis free of any magnetic attractive forces normally tending to move the disc magnet longitudinally along the axis, or alternatively to be located in a position to create a desired longitudinal attractive force. The entire assembly is maintained in operative positions by a circular belt which provides an inward facing lip on each side of which the stator assemblies are seated and which determines the magnetic airgap spacing for the disc. The invention may be implemented as a servo-actuator by the inclusion of an angular position sensor that uses the actuator rotor as the magnetic field emitter, and a receiver for the magnetic field and its contacts, located in the belt lip.

Description:
FIELD 
       [0001]    The invention relates to electromagnetic actuators and servo-actuators. 
       BACKGROUND 
       [0002]    Limited angle, brushless DC rotary actuators are well known and commercially available. One such actuator is disclosed in U.S. Pat. No. 5,512,871 issued Apr. 30, 1996. Another is disclosed in U.S. Pat. No. 6,313,553 issued Nov. 6, 2001. 
         [0003]    The actuators now available and as presented by the above-identified references, are known commercially as “torque motors”, and include a ferromagnetic yoke attached to a magnet comprising the rotating member. The yoke is deemed necessary in order to strengthen the rotating member sufficiently for operation, and to close the attached magnet&#39;s magnetic circuit. But the presence of a yoke results in a structure with a high moment of inertia, reducing dynamic performance, and having a single-sided stator structure which creates unbalanced magnetic forces on the rotating member attracting it toward the stator. 
         [0004]    One drawback of such an actuator is that approximately 20% or more of the power consumption is used to move its own inertia, reducing dynamic performance. Depending on the application duty cycle, this wasteful power consumption value can be even higher. 
         [0005]    A second drawback is that due to the unbalanced design, the rotor magnet has a magnetic attraction force toward the stator structure, which leads to the use of an expensive thrust ball bearing to perform an axial stop function yet allowing the requisite rotational freedom of the rotor. A part of this axial attraction force is useful to withstand vibration when used in certain applications, but in any case the rotor rotation is subjected to friction torque such that some of the magnetic force used to create rotation and output torque is wasted. 
         [0006]    A third drawback is the electromagnetic flux leakage. It can be clearly understood by seeing the structure of the prior art as in  FIG. 1  and  FIG. 2 , in that the 4 coils and stator poles are necessarily located very close to each other. Even with a small magnetic airgap between the rotor yoke and poles, when saturation appears at high currents necessary for the creation of high torque, most of the coil flux does not pass through the magnet, which would create the torque, but instead closes itself on the neighboring coil. 
         [0007]    A fourth drawback is that in servo applications, the actuator magnet cannot be used to activate the position sensor receiver, but a second, separate magnet is required to be attached to the yoke, adding cost and weight to the rotating member. 
         [0008]    A fifth drawback is that due to the physical space required for the construction and assembly of the stators and coils, the actual useful stroke of the prior art&#39;s 4-pole single-sided actuator is approximately 75 degrees compared to a theoretical stroke of 90 degrees, which would be preferable in most applications. Use of the prior art&#39;s 2-pole construction in the same physical actuator size could produce a 90 degree usable stroke, however the torque would be reduced by 50% rendering such an actuator undesirable and unusable in many applications. And, increasing the size of the actuator to attain the required torque would also render the actuator undesirable due to the resulting size, weight and cost. 
       SUMMARY OF THE INVENTION 
       [0009]    The following definitions are applicable in describing the invention unless the context indicates otherwise, and are known and understood by those skilled in the art of motor design: 
         [0010]    The term “stator” means a one or multi piece(s), high permeability ferromagnetic structure, which is fixed in linear or rotational motion. 
         [0011]    The term “active stator” means a “stator” with poles and adapted to receive excitation coil windings to produce a magnetic flux. 
         [0012]    The term “passive stator” means a “stator” that provides a path for a magnetic flux but does not incorporate any excitation coil windings. For example a “passive stator” can be high a permeability ferromagnetic plate. 
         [0013]    The term “stator circuit” means an “active stator” plus excitation coils placed on the poles. 
         [0014]    The term “stator assembly” means an overmolded “stator circuit” or an overmolded “passive stator”. 
         [0015]    The term “airgap” or “magnetic airgap”, with notation E, means the distance between axially spaced stators absent the rotor. 
         [0016]    The term “pole pair” means the north and south poles of a magnet. 
         [0017]    The term “multipolar” means a magnet that has been magnetized to have more than one pole pair. 
         [0018]    The term “rotor” or “rotor magnet” or “disc magnet rotor” means a multipolar disc magnet axially magnetized having pole pairs defined by a radial demarcation or transition line. 
         [0019]    The term “application” means a device to which the actuator is attached and which is operated by the actuator. 
         [0020]    The term “2 pole configuration” or “2 pole actuator” or the like means an embodiment in which there is at least a single 2 pole active stator on one side of the rotor and the rotor has two pole pairs. 
         [0021]    The term “4 pole configuration” or “4 pole actuator” or the like means an embodiment in which there is at least a single 4 pole active stator on one side of the rotor and the rotor has four pole pairs. 
         [0022]    The term “inertia assembly” means all the actuator parts that contribute to calculation of inertia for purposes of calculating the figure of merit AK. 
         [0023]    The present invention in one embodiment relates to an electromagnetic actuator comprising a rotary single-phase actuator that can produce a substantially constant torque and a torque proportional to current, on a limited angular travel known as its useful stroke, said useful stroke typically between 60 degrees and 110 degrees. The actuator comprises stators including 2 or 4 poles that are axially spaced apart, facing each other and their spacing establishing an airgap and a rotor consisting of a magnetized multipolar disc magnet of 2 or 4 pole pairs in the airgap. Other features and embodiments will be described below. 
         [0024]    In another embodiment, there is an active stator on one side of the rotor and a passive stator on the other side of the rotor. 
         [0025]    The end points of the travel of the application to which the invention is connected, whether rotary or linear, are mechanically connected to the appropriate beginning and end points of the actuator&#39;s useful stroke. The rotation of the actuator can also be limited to its useful stroke by internal stops. Applications of the actuator use its output torque to provide direct rotary motion, or may use a rotary-to-linear mechanism such as a cam and follower or crank and slider to convert the rotary motion&#39;s torque to a linear motion force. 
         [0026]    The invention produces a constant torque and a torque proportional to current over its useful stroke with equal or higher torque and faster dynamic response time, in a substantially equivalent size to actuators of the prior art. In one embodiment a 90° constant torque proportional to current, over a 90° useful stroke is available. In other embodiments a shorter stroke with constant torque is available. 
         [0027]    The invention finds particular application in controlling various automotive applications, such as air control and exhaust gas recirculation valves, and turbocharger vanes and waste gates. 
         [0028]    The invention is based on the realization that use of a stator on opposite sides of the rotor can enable greater dynamic effect than in the prior art in an equivalent size and space and avoid the problems seen in the prior art. In accordance with the principles of this invention, rather than attaching the rotating magnet to a ferromagnetic yoke, the yoke is eliminated. Two stationary, high permeability ferromagnetic magnetic stator assemblies, oppositely facing on either side of the rotor, are used. The use of stator assemblies on each side of the disc magnet rotor eliminates the ferromagnetic yoke utilized in the prior art. 
         [0029]    When at least one stator assembly is energized, actuator torque is achieved because of the affect of the stator assembly&#39; interaction with the rotor&#39;s magnetic field. In one embodiment the stator assemblies are alike; however embodiments with unlike stator assemblies are also useful as described below. 
         [0030]    The invention utilizes an airgap E between the closest surfaces of the axially spaced apart oppositely facing stator assemblies with the disc magnet rotor in the airgap defining a spacing e 1  and e 2  on either side of the disc magnet rotor. In one embodiment, e 1 =e 2 . However, as will be seen in the following description, there are times when it is beneficial to have unequal spacing such that e 1 ≠e 2 . 
         [0031]    In a magnetic structure such as this invention, there are “static” axial magnetic forces attracting the rotor magnet to the stator on each side, when there is no current applied to the stator excitation coils and also when the coils are energized. When current is applied to the coils, the coils are energized thereby generating their magnetic fields, and the interaction of those fields with the field of the rotor magnet creates the torque to rotate the shaft and drive the application. 
         [0032]    Management of the axial forces between the rotor magnet and the adjacent stator assemblies on each side is a feature of the invention. The static axial magnetic forces acting between the rotor magnet and the stator assemblies are determined by the type of stator assembly used on each side of the rotor, and/or the axial location of the rotor in the airgap E. In some applications such as automotive applications, it may be desirable to introduce an axial “pre-load” force on the shaft to help counteract axial vibrations. The introduction of such a biasing force is easily accomplished in this invention either by locating the rotor slightly closer to one stator assembly, or using two somewhat dissimilar stator assemblies to exert unbalanced axial forces to bias the rotor toward one stator assembly. The introduction of such a biasing force does not reduce the output torque of this invention. 
         [0033]    In an embodiment of the invention the positions of the stator assemblies on each side of the rotor is provided by a non-magnetic circular wrapping belt which has an inward-facing lip, which may be continuous or discontinuous, having a width equal to the magnetic airgap E. The lip has bearing surfaces against which the stator assemblies are seated thus allowing easy actuator assembly, and resulting in high dimensional precision, as well as low production cost. Thus, the magnetic airgap E is defined by the width of the inward-facing lip of the belt. 
         [0034]    In an alternative embodiment, the stator assembly on one side of the rotor can be a suitable high permeability ferromagnetic plate (a passive stator) of a thickness which is chosen to close the magnetic circuit. If a high permeability ferromagnetic plate is used, the amount of actuator torque is reduced from that provided by the embodiments having active stators on each side of the rotor since there are no coils on the plate for creating additional magnet flux. 
         [0035]    As described above the stator circuits are similarly overmolded in a non-magnetic material to make the stator assemblies, and along with the rotor and shaft, are assembled and connected by the aforementioned non-magnetic circular wrapping belt. 
         [0036]    However, in another embodiment, in order to create an integrated stator assembly, the overmolding of a first stator circuit also incorporates on the base side of the stator circuit, commonly molded with the normal overmolding, portions of the belt that serve to allow attachment and spacing of the other stator assembly. The belt and a lip bearing surface along with mounting ears is commonly molded with the overmolding on the pole face side of the stator circuit to define the integrated stator assembly. There can be 2, 3, or 4 mounting ears, respectively spaced apart at 180°, 120°, or 90° as part of the common molding as well as other features of the belt that may be desired. In this embodiment, after assembling the rotor and shaft into the integrated stator assembly, the second separately overmolded stator assembly is seated against the belt&#39;s lip bearing surface to define the magnetic airgap E, again allowing easy assembly, high dimensional precision, and low production cost. 
         [0037]    The non-magnetic wrapping belt and the spacing lip may contain an embedded rotor position sensor receiver, locating the sensor proximate to the actuator&#39;s magnetic airgap E, to receive varying magnetic field information utilizing the actuator rotor&#39;s magnetic flux. In this embodiment, the actuator rotor magnet either has a non-circular cross section, e.g. elliptical, in order to present a varying airgap and thus a varying magnetic field for the sensor, or has a particular magnetization pattern on its edge. This embodiment eliminates the need for locating a second emitter magnet and sensor receiver, with their attendant cost and space penalties, at one end of the actuator shaft. 
         [0038]    Given the foregoing, the following basic description of a two-pole rotary actuator with two active stators according to the invention is provided. The output torque of the actuator is developed by applying the principles of the Lorentz Force Law, known to those skilled in the art of motor design. The rotor magnet is magnetized axially through its thickness. The magnetization is realized with a magnetizing head. The stator poles are wound with copper or aluminum magnet wire, but in opposite winding directions, so when energized, poles of different polarities will be induced in each stator assembly. A stator assembly is located on each side of the rotor being axially spaced apart and facing each other to define the airgap in which the rotor resides. When energized, the facing poles of the stator assemblies on each side of the rotor are of opposite polarity and each rotor magnet pole will be facing an opposite polarity stator pole. The magnetic flux created by the energized coils interacts with the magnetic flux of the rotor magnet to create the output torque of the actuator. 
         [0039]    With a two pole design, the invention will have a total stroke of 180 degrees and within that stroke will be a 90 degree period where the torque is constant and proportional to the applied current. This is the useful area for control of various applications such as automotive air control valves, exhaust gas recirculation valves, and automotive variable geometry turbochargers and wastegates. 
         [0040]    The invention can also be implemented in a 4 pole configuration, with 4 poles on at least one stator assembly having alternating polarity and 4 pole pairs in the rotor of alternating polarity. With a 4 pole design, the total stroke will be 90 degrees with a useful, constant torque and proportionality period of 50 degrees. 
         [0041]    The rotor magnet, while high strength to withstand shock and vibration forces, has low inertia compared to prior art designs utilizing a ferromagnetic yoke. The employment of stator assemblies on each side of the rotor providing a concentrated magnetic flux to interact with the rotor provides high output torque. Thus, the dynamic performance of this invention is superior to prior art designs and provides much more precise control of the application to which it is applied along with more torque. 
         [0042]    Other embodiments of the invention provide a means in the form of a belt with a lip to establish the airgap distance. 
         [0043]    Other features and embodiments of the invention will be described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]      FIG. 1  is a cross-section view illustrative of a prior art actuator. 
           [0045]      FIG. 2  is a view of a prior art stator, pole and coil configuration. 
           [0046]      FIG. 3  shows a perspective view of an exemplary actuator of the present invention. 
           [0047]      FIG. 4  is an exploded view of exemplary components for the present invention. 
           [0048]      FIG. 5  is a perspective view of an exemplary stator structure of the present invention. 
           [0049]      FIG. 6  is a perspective view of an exemplary stator circuit of the present invention. 
           [0050]      FIG. 7  is a perspective view of an exemplary overmolded stator assembly of the present invention. 
           [0051]      FIG. 8  is a cross section view through  8 - 8  of  FIG. 3 . 
           [0052]      FIG. 9  is a schematic side view from arrow A of  FIG. 5  of the stator structure. 
           [0053]      FIG. 10   a  is a view showing a non-circular rotor magnet as the magnetic emitter with a sensor receiver located in the belt to determine rotor angular position. 
           [0054]      FIG. 10   b  is a schematic view showing a portion of the rotor having varying magnetization along a peripheral portion as the magnetic emitter with a sensor receiver located in the coupling belt to determine rotor angular position. 
           [0055]      FIG. 11  is a perspective view of the coupling belt. 
           [0056]      FIG. 12  is partial perspective view of the stator coupling belt. 
           [0057]      FIG. 13  is an exploded perspective view of an embodiment of the present invention where the rotary position receiver is mounted to a printed circuit board or lead frame in the cover and a magnetic field emitter is mounted to the shaft. 
           [0058]      FIGS. 14   a  and  14   b  show the operation of a 2 pole embodiment of the invention in which  FIG. 14   a  shows the ready position at −45° from the middle of the stator pole and  FIG. 14   b  shows the final position when the coils are energized, at +45° from the middle of the stator pole. 
           [0059]      FIG. 15  is a graph of the torque curves for a 2 pole embodiment of the invention. 
           [0060]      FIG. 16   a - 16   c  show views of a 4 pole embodiment of the invention in which  16   a  is a perspective view;  16   b  shows the ready position at −25° from the middle of the stator pole;  16   c  shows the final position when the coils are energized, at +25° from the middle of the stator pole. 
           [0061]      FIG. 17  is a graph of the torque curves for the 4 pole embodiment of the invention 
           [0062]      FIGS. 18   a - 18   c  are views of an embodiment of the invention using 2 asymmetric stator structures in which  FIG. 18   a  is a perspective view of the assembled apparatus;  18   b  is a perspective view of one the asymmetric stator structures of  FIG. 18   a  and  FIG. 18   c  is a perspective view of the other asymmetric stator structure of  FIG. 18   a.    
           [0063]      FIG. 19  is a view of an embodiment with an active stator on one side of the rotor and a passive stator in the form of a single plate on the opposite side of the rotor to close the magnetic circuit. 
           [0064]      FIG. 20  is a view of an embodiment where the actuator is directly driving an air control valve in rotary motion. 
           [0065]      FIG. 21  is a view of an integrated stator assembly embodiment in which the overmolding of one stator is commonly molded with the coupling belt. 
           [0066]      FIG. 22  is a partial view of an embodiment in which the spacing lip is discontinuous. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0067]      FIG. 1  is a cross section of an illustrative prior art actuator taken from FIG. 6 of U.S. Pat. No. 5,512,871. The actuator consists of a magnetized disc  102  which is glued to a ferromagnetic yoke  112  and thus constitutes the movable device  100 , which is connected to a coupling shaft  110 . The stationary part  108  comprises a stationary stator assembly. A thrust ball bearing  104  is necessary to limit the axial movement of the moveable device  100  toward the stationary stator assembly  108 . It is to be noted that the yoke rotates with the magnetized disc and thus introduces the problems mentioned above with respect to the prior art such as in U.S. Pat. No. 5,512,871 issued Apr. 30, 1996 and U.S. Pat. No. 6,313,553 the contents of which are incorporated in their entirety herein for all purposes. 
         [0068]      FIG. 2  is a view of a prior art stator circuit and shows the stator poles  206  mechanically pressed into a stator base  200 . The four stator poles  206  each have a pole shoe  202  at the level of their heads in order to reach the maximum angular travel as close as possible to the ninety degree theoretical travel, which in the case of this prior art actuator is approximately only 75 degrees. The electric supply coils  204  used for generating the magnetic flux for the actuator are placed on each of the four stator poles  206 . When saturation appears at high currents for the desired creation of high torque, most of the coil  204  flux does not pass through the rotor magnet, which would create the torque, but instead closes itself on the neighboring coil  204 . 
         [0069]      FIG. 3  shows a general view of the actuator  10  in an embodiment in accordance with the principles of this invention. The actuator comprises first and second like overmolded stator assemblies  12  and a coupling belt  14  and other components all as further described in  FIG. 4 . 
         [0070]      FIG. 4  is an exploded view of an exemplary embodiment of the present invention  10 . The actuator comprises first and second overmolded stator assemblies  12 , a coupling belt  14  and a magnetized disc rotor  16 . Disc rotor  16  is attached to shaft  18  by coupling member  20  to apply its rotation to the shaft. The rotor  16  is located in an airgap between the two stator assemblies  12  defined by the coupling belt  14  by an inward facing lip  22  and bearing surfaces  24  and  26  which are illustrated in  FIGS. 8 ,  11  and  12 . The first and second bearing surfaces  24  and  26  against which both stator assemblies  12  are seated defines the airgap E. Coupling belt  14  in one embodiment is configured as a sufficiently rigid circular belt as will become clearer hereinafter. It has cutout ears  28  with openings for engaging clips as will be described below. The stator assemblies  12  are positioned in the belt from opposite directions and seat on the corresponding bearing surfaces  24  and  26 , as shown, in a manner which defines a magnetic airgap E for disc magnet rotor  16  which is positioned with respect to the bearing surfaces  24  and  26 . The dimension e 1  and e 2  are the distances from the stator pole end faces  36  (see  FIG. 5 ) to the facing surface of the rotor. In typical embodiments, disc magnet rotor  16  is located in the center of the magnetic airgap E equally spaced from the stator assemblies, that is, e 1  equals e 2 . It is understood that the shaft  18  is axially fixed with respect to the stator assemblies  12 , and that the rotor  16  is also axially fixed and coupled on the shaft  18  so that when the unit is assembled the rotor  16  is in an axially fixed position within the magnetic airgap E. In typical applications, the rotor  16  will be maintained without any net axial force due to the symmetry of the magnetic forces provided by equal spacing and axially symmetrical like stator assemblies on each side of the rotor. However, in certain applications of the invention such as when there is a vibration environment, it may be advantageous to introduce an axial force on the rotor  16  to resist vibration in one direction and thereby to help maintain the application&#39;s load in its axial location. To resist vibration in one direction, the location of disc magnet rotor  16  on the shaft  18  can be axially adjusted, toward either stator assembly  12 , to provide the desired axial force on the rotor  16 , with no reduction of output torque. Another means for inducing an axial force on the rotor  16  is described below with reference to  FIGS. 18   a - 18   c . This adjustment of the axial force on the rotor can be implemented in both the 2 pole and the 4 pole configuration. 
         [0071]    It is to be noted that in the applications for which this invention is intended, a high dynamic response capability is an important requirement in order to position the application in as short a time as possible. A measure of the ability of the actuator to produce the required torque and to position the application to its commanded position is provided by the use of figures of merit, and herein, a figure of merit AK is defined which has an absolute numerical value equal to or greater than about 1,000 and is calculated by the ratio of Motor Steepness divided by Motor Inertia J m , where Motor Steepness is equal to the square of the Motor Constant K m . 
         [0000]    
       
         
           
             
               AK 
               = 
               
                 
                   
                     Motor 
                      
                     
                         
                     
                      
                     Steepness 
                   
                   
                     Motor 
                      
                     
                         
                     
                      
                     Inertia 
                   
                 
                 = 
                 
                   
                     
                       Motor 
                        
                       
                           
                       
                        
                       
                         Constant 
                         2 
                       
                     
                     
                       Motor 
                        
                       
                           
                       
                        
                       Inertia 
                     
                   
                   ≥ 
                   1 
                 
               
             
             , 
             000 
           
         
       
     
         [0000]    K m  describes the motor&#39;s ability to produce output torque based on input electrical power and is an intrinsic figure of merit useful to compare different motors. K m  is proportional to the ratio of output torque (T) to the square root of input power (W), i.e. 
         [0000]    
       
         
           
             
               K 
               m 
             
             = 
             
               
                 T 
                 
                   W 
                 
               
               . 
             
           
         
       
     
         [0000]    J m  is the sum of the rotor  16  inertia and the shaft  18  inertia and the coupling member  20  inertia as can be seen in  FIG. 4 . Motor constant K m , Motor Steepness, Motor Inertia J m , Torque T and input power W are terms and figures of merit known to those skilled in the art of motor design. 
         [0072]    An exemplary actuator of a 2 pole configuration as described herein may be constructed with parameters as in Table 1 to provide the figure of merit AK at least equal to 1,000. In the example given: 
         [0000]    
       
         
           
             
               AK 
               = 
               
                 
                   
                     
                       ( 
                       
                         1.73 
                         × 
                         
                           10 
                           
                             - 
                             1 
                           
                         
                       
                       ) 
                     
                     2 
                   
                   
                     1.85 
                     × 
                     
                       10 
                       
                         - 
                         5 
                       
                     
                   
                 
                 = 
                 1 
               
             
             , 
             618 
           
         
       
     
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Torque Motor comparison 
                   
                 PRIOR ART 
                 INVENTION 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Magnet remanence 
                 (T) 
                 1.2 
                 1.2 
               
               
                 Torque constant = Kt 
                 (Nm/A) 
                   
                 0.243 
               
               
                 Terminal resistance 
                 (Ohms) 
                   
                 1.98 
               
               
                 Motor constant = Km peak 
                 (Nm/W 1/2 ) 
                 1.50E−01 
                 1.73E−01 
               
               
                 Rth 
                 ° C./W 
                   
                 2.50 
               
               
                 Continuous torque @ 25° C. 
                 (Nm) 
                   
                 1.221 
               
               
                 and 12 V 
               
               
                 Continuous torque @ 130° C. 
                 (Nm) 
                   
                 0.430 
               
               
                 and 12 V 
               
               
                 Peak torque @ 130° C. and 
                 (Nm) 
                   
                 0.906 
               
               
                 12 V 
               
               
                 Stroke 
                 (°) 
                 75 
                 &gt;90 
               
               
                 Electrical time constant 
                 (ms) 
                 9.5 
                 4.3 
               
               
                 Inertia 
                 (kg.m 2 ) 
                 6.50E−05 
                 1.85E−05 
               
               
                 Mechanical time constant 
                 (ms) 
                 2.9 
                 &lt;1 
               
               
                 Diameter 
                 (mm) 
                 60 
                 60 
               
               
                 total height 
                 (mm) 
                 50 
                 72 
               
               
                 total weight 
                 (g) 
                 640 
                 550 
               
               
                 Magnet weight 
                 (g) 
                 46 
                 50 
               
               
                 Iron weight stator 
                 (g) 
                 340 
                 360 
               
               
                 Iron weight rotor 
                 (g) 
                 140 
                 0 
               
               
                 Copper weight (all coils) 
                 (g) 
                 60 
                 80 
               
               
                   
               
             
          
         
       
     
         [0073]      FIG. 5  is a view of the stator structure  30  of the present invention which advantageously may be made by the sintered powder metal process. In this exemplary version, the stator structure  30  has two poles  32  and a base  34 . The poles  32  have end faces  36 . The stator structure  30  defines a U-shaped configuration. 
         [0074]      FIG. 6  is a view of a stator circuit  40  of a 2 pole configuration of the present invention showing coils  42  wound on molded bobbins  44  and terminated in pins  46  to provide access for electrical connection. The bobbins  44  are mounted on the poles  32  of the stator structure  30 . 
         [0075]      FIG. 7  is a view of the overmolded stator assembly  12  of the present invention for a 2 pole configuration. In this view stator pole end faces  36  and coil connections  46  are visible. 
         [0076]    The overmolding material  44  may be a thermoplastic polymer of the Liquid Crystal Polymer (LCP) type, a commercial example being Zenite, or a thermoplastic polyamide formulation, commercially known examples being Stanyl and Zytel. The overmolding  44  makes it possible to provide a mechanical connection of the overmolded stator assembly  12  with the belt  14  or a cover  48  ( FIG. 13 ) by the presence of fastener elements in the form of protruding grippers or clips  50  on which mating fastener elements in the form of cutout ears  52  ( FIG. 11 ) of the coupling belt  14  or the cutout ears  54  of the cover  48  ( FIG. 13 ) are fastened. While the mating fasteners hold the parts together, it is the lip  22  ( FIGS. 11 and 12 ) that defines the precise dimension of the airgap E. The airgap E is the distance between facing stator pole end faces, or between stator pole end faces on one side and a passive stator on the other side of the rotor as will be described in more detail below. In the present embodiment, because the overmolding is coplanar with the stator pole end faces, the dimension E is determined by the width of the lip  22  having its bearing surfaces  24  and  26  bearing on the overmolding of the stator assemblies. In any configuration the width of the lip may be adjusted to ensure that the dimension E is the distance between pole end faces or pole end faces and a passive stator as the case may be. It should be noted that in addition to the mechanical connection of the stator assemblies  12  with the coupling belt  14 , there is a magnetic axial force between the stator assemblies  12  and the rotor  16  which contributes to holding the actuator  10  together and in particular to cause the stator assemblies  12  to firmly seat on the bearing surfaces  24  and  26  of the lip  22 . 
         [0077]      FIG. 8  is a cross section view through  8 - 8  of  FIG. 7 . In this view, the U-shape of the cross section through the stator poles  36  is evident. The magnetic airgap E is determined by engagement of the lip sides  24  and  26  with the overmolded stator assemblies  12 . The magnetic flux circuit FC flows efficiently through the stators. 
         [0078]      FIG. 9  is a schematic view along arrow A of  FIG. 3  of the stator structure  30  showing the U-shaped cross section and defining key dimensions D and H. Dimension D is the spacing between the poles  36  and is in the range of about 2 to 5 times the magnetic airgap E, and preferably is about 4 times the magnetic airgap E providing sufficient spacing to prevent electromagnetic flux leakage between the energized coils. Dimension H is the height of the stator pole  36  above the base  34  and is less than about 8 times the magnetic airgap E and preferably about equal to or less than 6 times the magnetic airgap E allowing the energizing coil to have sufficient copper volume for operation of the invention. 
         [0079]    It is also to be noted that prior art rotary actuators may also be equipped with angular position sensors. This type of configuration is often called a servo-actuator. Such a sensor requires an additional magnet mounted on the rotating yoke and a sensor receiver attached to the actuator cover. A feature of actuators in accordance with the principles of this invention is the absence of the additional magnet. A sensor receiver is located in a position in the belt  14  in energy coupling relationship to the magnetized disc magnet rotor  16  as is discussed below. 
         [0080]      FIG. 10   a  is view showing a non-circular magnet rotor  56  functioning as the magnetic emitter for the sensor receiver  58  to determine rotor angular position. The sensor  58  is mounted in the belt  14 . The use of a non-circular, for example elliptical, rotor creates a varying distance between the rotor  16  and the sensor receiver  58  whereby the consequent varying magnetic field strength information is utilized to determine angular position information. The non-circular configuration is illustrated by the dimension D 1  being greater than the dimension D 2 . 
         [0081]      FIG. 10   b  is another way to provide the varying magnetic flux signal to the sensor  58 . In this embodiment, a portion  60 N and  60 S of each pole is magnetized with a progressively or discretely varying changing magnetic field strength as the magnetic emitter so that the sensor  58  receives the varying flux as a varying signal, the dash lines schematically depicting the variation. 
         [0082]      FIGS. 11 and 12  are views of the belt  14 . The belt material may be of a thermoplastic polyester, such as DuPont Crastin PBT. The central lip  22  spaces the stator assemblies  12  apart to fix the magnetic airgap E as seen in  FIG. 8 . Cutout ears  52  are used to clip onto grippers  50  of the stator assemblies  20 . Electrical connections to the stator circuit coil pins  46  are carried out in the areas  62 . If a sensor receiver  58  is mounted in the belt  14 , areas  62  may also be used for its electrical connections. The lip  24  is shown as a continuous element, but it could be discontinuous so long as there are enough portions of the surfaces  24  and  26  to maintain the airgap E. This is illustrated in  FIG. 22  in which lip segments  64  are spaced apart. 
         [0083]      FIG. 13  is an exploded view of another embodiment of the present invention  10  where the angular position receiver  58  is mounted to a printed circuit board or leadframe  66  in the cover  48  and a magnetic field emitter  68  is mounted to the end of shaft  18 . Cutout ears  54  mechanically fix the cover  48  to the stator assembly  20  by clipping onto grippers  50 . 
       Now the Operation of the Actuator Will be Described. 
       [0084]      FIGS. 14   a  and  14   b  show schematic views of the magnetic poles of the stators  36   a  and  36   b  and the two pole pairs  70  of rotor  16  in the various operating positions for a 2 pole configuration. The demarcation or transition of the magnetic pole pairs in the rotor  16  is shown at  72 . In  FIG. 14   a  the rotor  16  is in a ready position relative to the stators  36   a  and  36   b , which in an initial ready state are not energized. The ready position is at nominally −45° to the center of the pole  36   a . The rotor  16  is at one end of its useful stroke because of its connection to one extreme position of the user application, e.g. an air valve “fully open”. As seen in  FIG. 8 , to operate the actuator the stators  36   a  and  36   b  will be energized as N and S poles respectively and the stators  36   c  and  36   d  will be energized as S and N poles respectively. That will cause the rotor to rotate in the direction of the arrow R. This will rotate the shaft  18  to operate the user application.  FIG. 14   b  shows the position of the rotor  16  after rotation to the other end of its useful stroke, to a final position at nominally +45° to the center of the pole  36   a  which is the other extreme position of the application, e.g. an air valve “fully closed”. If the current is removed from the coils, a mechanical means such as a spring may be employed to cause the actuator to return to the first ready position. Typically the application equipment will provide the return spring, although the actuator can have it built-in. 
         [0085]      FIG. 15  is a graph of a 2 pole rotary actuator according to the invention that is, 2 stator poles on each side of the rotor and the rotor having 2 pole pairs. In the graph, the 90° useful stroke has substantially constant torque, and the torque is proportional to the applied current, and in the art is taken as a constant torque actuator. 
         [0086]      FIGS. 16   a - 16   c  illustrate a 4 pole configuration  74  of the invention; that is 4 stator poles on each of the stator assemblies  76   a  and  76   b  on each side of the rotor  78  and the rotor  78  having 4 pole pairs. Although the belt  14  is not shown in this figure, when installed it would define the airgap space E.  FIG. 16   b  shows the start position for the 4 pole configuration, at nominally −25° from the center of the stator pole, and  FIG. 16   c  shows the final position at nominally +25° from the center of the stator pole. Typically the 4 pole configuration has a useful stroke for constant torque of approximately 50 to 65 degrees. 
         [0087]      FIG. 17  is a graph of a 4 pole rotary actuator according to the invention. In the graph a 50° useful stroke of constant torque is depicted. 
         [0088]      FIGS. 18   a - 18   c  show an asymmetric embodiment  80  of the invention. In the asymmetric embodiment as shown by comparing  FIGS. 18   b  and  18   c , the stator poles  82  on one side of the rotor  16  are larger than the stator poles  84  on the other side. This results in an axial attraction force on the rotor  40  toward the larger stator poles, which is useful to resist vibration from the user application. Although a 2 pole configuration is shown, the asymmetry can be similarly implemented in a 4 pole configuration. 
         [0089]      FIG. 19  shows another embodiment  90  of the invention in which the rotor  16  has a stator assembly  12  on one side of the airgap E and a passive stator assembly  94  exemplified with a ferromagnetic plate  96  on the other side. This embodiment provides a lower cost actuator but with lower torque. The passive stator can be constructed in any form that has a surface opposite the end faces of the active stator assembly. For example a 2 pole stator without coils could be used. It can appreciated that with a passive stator the airgap dimension E is the distance between the end faces of the active stator poles and the opposite surface of the passive stator. This is shown in  FIG. 19  in which the stator assembly  12  is on one side of the rotor  16  and a passive assembly  94  is on the opposite side with the plate  96  serving as the passive stator. The actuator may be attached to an operated device of the type in which the equipment directly drives the application in a rotary movement, or converts the rotation of the shaft to linear motion.  FIG. 20  schematically shows the actuator  10  attached to an operated device  100  of the type in which an operated part  102  is directly rotated by the rotation of the shaft  104 , along with a stop mechanism  106 . This would be exemplified by an on-off butterfly air valve. 
         [0090]    Either of the types of equipment, rotary or linear, can be used with the servo actuator version of the invention in which the amount of rotation or linear movement of the equipment and the amount of rotation of the rotor is sensed by the sensor and commands are given by a control system to change the rotational position of the rotor and consequently of the served equipment. 
         [0091]    Examples of rotary control applications using the actuator&#39;s output torque are air or exhaust gas recirculation (EGR) control valves, turbocharger variable geometry vane or waste gate control, or throttles utilizing a “butterfly valve” configuration. 
         [0092]    Rotary-to-linear motion may be accomplished via a “crank and slider” mechanism or by a rotating cam with a roller follower producing the linear motion and force. EGR valves of the pintle type and variable geometry turbochargers are examples of automotive applications that can utilize this invention. 
         [0093]    These applications typically have a “home” position, maintained with no power applied to the actuator, and a powered end-of-stroke position where the application is at its maximum value. The invention will be controlled to take a position anywhere along the stroke, and will rapidly move back and forth along the stroke as commanded. A “fail safe” return spring is often incorporated in the application to return the actuator to its home position in the event of a power failure and when power is purposely shut down. In the absence of a return spring, the actuator can hold its end-of-stroke position, at either end, without power being applied. 
         [0094]      FIG. 21  illustrates an integrated version of the invention in which the overmolding  44  of the stator assembly is molded commonly with the belt  14  to create an integrated part  110  that is, the belt and stator assembly as an integrated structure. In this embodiment, the shaft, the rotor and the opposite stator assembly are conveniently assembled to the integrated part  110 . This enables easy assembly and eliminates one dimensional tolerance variation in establishing the airgap space E. 
         [0095]      FIG. 22  illustrates the embodiment of the belt  14  in which the lip is discontinuous as shown by the spaced apart lip segments  64 . 
         [0096]    The foregoing Detailed Description of exemplary and preferred embodiments is presented for purposes of illustration and disclosure in accordance with the requirements of the law. It is not intended to be exhaustive nor to limit the invention to the precise form or forms described, but only to enable others skilled in the art to understand how the invention may be suited for a particular use or implementation. The possibility of modifications and variations will be apparent to practitioners skilled in the art. No limitation is intended by the description of exemplary embodiments which may have included tolerances, feature dimensions, specific operating conditions, engineering specifications, or the like, and which may vary between implementations or with changes to the state of the art, and no limitation should be implied therefrom. This disclosure has been made with respect to the current state of the art, but also contemplates advancements and that adaptations in the future may take into consideration of those advancements, namely in accordance with the then current state of the art. It is intended that the scope of the invention be defined by the Claims as written and equivalents as applicable. Reference to a claim element in the singular is not intended to mean “one and only one” unless explicitly so stated. Moreover, no element, component, nor method or process step in this disclosure is intended to be dedicated to the public regardless of whether the element, component, or step is explicitly recited in the Claims. No claim element herein is to be construed under the provisions of 35 U.S.C. Sec. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for . . . ” and no method or process step herein is to be construed under those provisions unless the step, or steps, are expressly recited using the phrase “comprising step(s) for . . . ”