Abstract:
A pancake type direct current motor is disclosed which comprises a motor drive shaft with one or more rotor assemblies secured along the motor drive shaft. An even number of spaced stator poles surrounds each of the one or more rotor assemblies. Each stator pole has an associated excitation winding, with all of the stator poles of a given stator assembly having the same polarization (i.e. north or south). Each of the one or more rotor assemblies comprises at least two pairs of rotor legs uniformly space and extending radially outward from the motor drive shaft. The angular spacing between each of said pairs of rotor legs being equal to or somewhat less than the spacing between adjacent stator poles. Each one of a pair of rotor legs has an excitation winding. The excitation windings of the two legs are oppositely polarized so that successive stator poles about the rotor are alternating north and south poles. A rotor position sensor reports the instant rotor position to a sequencing and control system. The control system responds to the rotor position by energizing and de-energizing the excitation windings to sustain the operation of the motor.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to electrical machines of the rotary type and, more particularly, to motors powered by direct current, preferably supplied from batteries. 
     DESCRIPTION OF THE PRIOR ART 
     Electrical motors are currently used to provide motive power in many familiar devices ranging from small actuators to large industrial systems and including transportation vehicles such as urban railroads. In many cases, provision of electrical power to such motors presents no serious problem such as in stationary motor installations or where the power requirements are small and battery power is feasible and relatively economical. In transportation vehicles, however, some difficulties arise due to the mobile nature of the application and the amount of power required. For that reason, the use of electrical motors in vehicles has only become widespread where power can be supplied through a stationary structure to which the vehicle&#39;s motion is constrained, such as in electrically powered railway vehicles. 
     If the vehicle motion is not so constrained, as in automobiles, power must be provided from batteries which are carried in the vehicle, adding significantly to vehicle weight in an amount often comparable to or greater than the payload of the vehicle. During use of the vehicle, the weight of the vehicle and payload, as well as the batteries, must be accelerated repeatedly, requiring substantial amounts of power simply for the transportation of the batteries themselves. Accordingly, efficiency of the motor becomes of paramount importance in such applications in order to develop an acceptable range and operating time of the vehicle for each recharge of the batteries. 
     The ability to control operating speed of a motor is also of special importance in many applications, including transportation vehicles. While alternating current motor designs have been able to achieve relatively high efficiencies, motor speed in alternating current machines is largely controlled by the frequency of the voltage used to power the machines and only a limited amount of slip (e.g. in induction motors) is tolerable. Variation of the power supply frequency is often impractical where the power is drawn from commercial electric power distribution systems and, in any event, the apparatus necessary for power frequency control over a wide range is extensive and eliminates much of the efficiency advantages of alternating current machines in applications where variable speed is required. 
     Direct current machines, on the other hand, can provide speed control by control of input voltage relative to the load with relatively simple electrical circuitry. In traditional DC motors using commutators, the geometry of the stator and rotor fields is substantially fixed and torque and speed vary with the applied voltage, the load which must be driven and the windage and other losses in the motor, itself. 
     In designs of stepping motors and in pancake motor designs, in particular, magnetic elements such as permanent magnets or elements of high permeance material are placed at periodically spaced locations on a rotor disk and a sequence of pulses applied to stators located periodically around the rotor and in registration with the path of the magnetic elements in order to attract and/or repel them to cause rotary motion of the rotor. 
     The availability of such d-c motors is particularly of interest at the present time for use in electric automobiles which are considered to offer a promising solution of the environmental problems associated with gasoline powered automobiles. 
     U.S. Pat. No. 5,545,936, issued Aug. 13, 1996 to the author of the present invention utilizes a pancake-like structure with the stators distributed about the circumference of the rotor in a manner similar to the arrangement of the presently disclosed structure. The present invention, however, employs pulsed electromagnets in the rotor whereas the device of U.S. Pat. No. 5,545,936 is a reluctance type machine. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a relatively high power motor that is operable from a relatively low voltage d-c source. 
     It is another object of this invention to provide such a motor in a form which is readily adaptable to applications requiring precise speed control over a wide range. 
     It is a further object of this invention to provide such a motor which will operate at high electrical efficiency. 
     A still further object of this invention is to provide such a motor in compact and light-weight form relative to its power capability. 
     Further objects and advantages of the invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be more readily described by reference to the accompanying drawings in which: 
     FIG. 1 is a functional illustration of a first version of the motor of the invention, this simplest form of the invention incorporating two pairs of rotor legs per rotor assembly, 
     FIG. 2 is a partially cut-away perspective drawing illustrating the geometries and physical arrangements of the rotor and stator magnetic core structures of the motor, 
     FIG. 3 is a longitudinal cross-sectional view of the motor of the invention illustrating additional details of construction including rotor and stator excitation, 
     FIGS.  4 A- 4 D are functional illustrations of the motor for different rotor positions, these illustrations being useful in the determination of rotor and stator excitation sequencing as required for effective and efficient motor operation, 
     FIG. 5 is a tabulation of rotor and stator excitation conditions as determined from FIGS.  4 A- 4 D and from an extension of this procedure through a complete rotor revolution, 
     FIG. 6 illustrates an optical sensor arrangement that may be employed to identify the instant rotor postion as needed to control rotor and stator excitations in the manner defined in FIG. 5, 
     FIG. 7 is a block diagram illustrating the power and control system of the motor. 
     FIG. 8 is a functional illustration of a second version of the motor of the invention, this version incorporating three pairs of rotor legs per rotor assembly. 
     FIG. 9 is functional illustration of one of the several stator assemblies employed in a motor assembly comprising three rotor assemblies of the type illustrated in FIG. 8, 
     FIG. 10 is a functional illustration of a third version of the motor of the invention, this version incorporating four pairs or rotor legs per rotor assembly, and 
     FIG. 11 is a functional illustration of a stator assembly of the type employed in the motor of FIG.  10 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring more particularly to the drawings by characters of reference, FIGS.  1 - 3  illustrate the basic structure of the preferred embodiment of the d-c motor  10  of the invention. The motor  10  which takes the general form of a pancake motor or a stack of pancake motors, comprises two rotor assemblies  11  and  11 ′ (as shown in FIG. 2 less their excitation windings) and eight stator members, ST 1 -ST 8  (again as shown in FIG. 2 with excitation windings omitted and with stator members ST 2 -ST 4  omitted to avoid obscuring other structural details). A magnetic spacer ring  21  separates the two rotor assemblies. 
     Each rotor assembly comprises a central magnetic ring  22  and four rotor legs, R 1 -R 4 . R 1  and R 2  form a first pair of legs; R 3  and R 4  form a second pair. The two pairs of legs are positioned diametrically opposite each other relative to the drive shaft  23  (FIG. 3) which passes through the central openings of spacer ring  21  and rings  22  of rotor assemblies  11  and  11 ′. The two legs of each pair are spaced 45 degrees (or less) apart with R 1  and R 3  linearly aligned and with R 2  and R 4  linearly aligned, all four legs extending radially outwardly relative to the shaft  23 . 
     Each of the rotor legs R 1 -R 4  has the general shape of a capital “T” with its top, radially-outward surface arcuately shaped to track the cylindrical inner bound  25  of the motor air gap  26  (FIG.  1 ). 
     The eight stator members ST 1 -ST 8  are uniformly spaced 45 degrees apart about the air gap. The width of each stator covers approximately 20 mechanical degrees, roughly matching the width of the top member of the T-shaped rotor leg. 
     As shown in FIG. 1, each rotor leg, R 1 -R 4  of rotor assembly  11  carries a rotor excitation winding  27 . The four excitation windings are shown serially connected across motor slip rings  28  (FIG.  3 ). As indicated in FIG. 1, the windings  27  of alternate rotor legs are oppositely polarized to produce alternate north (N) and south (S) rotor poles. Thus, for example, R 1  becomes a south pole and R 2  becomes a north pole with flux φ r  flowing inwardly through leg R 1  and flowing outwardly through leg R 2 . The excitation windings may be designed for serial connection as shown or they may be designed for parallel connection, as appropriate for a given application. 
     FIG. 3 shows the means by which stator excitation is provided for stators ST 1  and ST 5  and for the corresponding stators, ST 1 ′ and ST 5 ′ associated with rotor legs R 1 ′ and R 3 ′. Stator core member  31  which spans the air gap surfaces of rotor legs R 1  and R 1 ′ of rotor assemblies  11  and  11 ′, respectively, has a centered rectangular depression  32  which receives a stator excitation winding  33 . Winding  33  is connected across the terminals of a sequence and control circuit which provides a control voltage Vs, yet to be addressed. The resulting current passing through the winding  33  drives a flux, φ, which passes through the center of winding  33  to ST 1 , across the air gap, through rotor leg R 1 , through central ring  22  of rotor  11 , through spacer ring  21 , central ring  22 ′ of rotor leg R 1 ′, through the R 1 ′/St 1 ′ air gap to ST 1 ′ and back through the center of winding  33 . This establishes stator ST 1  as a north (N) pole and ST 1 ′ as a south (S) pole. In the same manner. ST 5  and ST 5 ′ are excited by means of a stator excitation winding  34  wound on stator core member  35 . Six additional stator core members and associated excitation windings provide excitation for the remainder of stator poles (ST 2 -ST 4 , ST 6 -ST 8 , and the corresponding poles associated with rotor assembly  11 ′. 
     It will be noted at this point that the angularly aligned stators ST 1  and ST 1 ′ are oppositely polarized, i. e. ST 1  is a north (N) pole while ST 1 ′ is south (S) pole; ST 2  is a south pole while ST 2 ′ is a north pole, etc. For this reason, corresponding legs of rotor assemblies  11  and  11 ′ must also be oppositely polarized, i. e. R 1  is a south pole, R 1 ′ a north pole, R 2  is a north pole, R 2 ′ is a south pole, etc. 
     Additional details of the motor assembly, as shown in FIG. 3, include the left and right housing members  36  and  37  which support the stator core members, and drive shaft bearings  38  and  39 . Rotor excitation is supplied by brushes (not shown) which ride upon the slip rings  28 . 
     Operation of the motor  10  is based upon the well-known principle that like poles (two north poles or two south poles) repel each other while two unlike poles (one north pole and one south pole) attract each other. 
     FIGS.  4 A- 4 D are useful in the determination of rotor and stator excitation sequencing requirements. The four figures show plan views of the motor  10  for four different rotor positions. As the rotor turns, it passes through eight sectors or periods in the course of each revolution, each period covering 45 degrees of rotation bounded by the center lines of two adjacent stator poles. The center line of rotor leg R 1  is employed as the rotational reference as indicated by the arrow  37 . 
     FIG. 4A shows rotor R 1  passing through period P 1  and rotating clockwise. As indicated by table  38 , all rotor poles R 1 -R 4  are energized during period P 1  and they remain energized throughout the complete revolution. The individual stator poles, however, are turned on or off during each period as appropriate for driving the rotor in the clockwise direction. 
     As shown in FIG. 4A, rotor leg R 1  is polarized as a south pole and is thus attracted by stator poles ST 1  and ST 2  when these stator poles are energized, with Sta urging R 1  counter-clockwise and ST 2  urging R 1  in the clockwise direction. For clockwise rotation, ST 1  is de-energized or turned off while ST 2  is turned on as shown for period P 1  of table  38 . 
     Stator ST 3  does not immediately interface with any rotor pole during P 1  and is therefore turned off during this period, again as shown in table  38 . 
     Rotor leg R 4 , which is energized as a north pole is repelled by both stator poles ST 4  and ST 5  with ST 4  urging the rotor clockwise and ST 5  urging the rotor in the counter-clockwise direction. ST 4  is thus turned on and ST 5  is turned off for clockwise rotation. 
     Stator pole ST 6  attracts the oppositely polarized rotor leg R 3  urging R 3  clockwise and is therefore turned on during period F 1 , again as shown in table  38 . 
     ST 7  does not immediately interface a rotor pole during P 1  and is therefore turned off as indicated. 
     ST 8  repels the north pole or rotor leg R 2  urging the rotor clockwise and is therefore turned on during P 1 . 
     During period P 2  as shown by FIG. 4B, stator poles ST 1 , ST 3 , ST 5  and ST 7  urge the rotor clockwise and are therefore turned off. Stators ST 4  and ST 8  do not interface the rotor during period P 2  and are also turned off. 
     The same procedure is applied to periods P 3  and P 4  as illustrated, respectively, by FIGS. 4C and 4D, and the same procedure is employed for the remaining periods, P 5 -P 8 . 
     The motor  10  can also be made to rotate in the counter-clockwise direction by appropriately energizing and de-energizing the stator poles. For counter-clockwise rotation the rotor poles will again be energized continuously and the stator poles will be turned on and off in a pattern that is complementary to that of table  38 , i. e. those stators that are turned off during nay given period for clockwise rotation will be turned on for counter-clockwise rotation and those that are turned on for clockwise rotation will be turned off for counter-clockwise rotation. 
     The conditions shown in table  38  for rotor poles R 1 -R 4  and for stator poles ST 1 -ST 8  apply also to rotor poles R 1 ′-R 4 ′ and stator poles ST 1 ′-ST 8 ′, respectively. 
     In order to control the rotor and stator excitation in accordance with table  38 , it is necessary to identify at all times the instant rotor position. A position sensor  39  for identifying the instant position of the rotor is shown in FIG.  6 . The position sensor  39  comprises a sensor plate  41 , a light source plate  42  and a revolving shield  43 . 
     Sensor plate  41  comprises a stationary disk secured to the frame of the motor in alignment with the eight stator poles, ST 1 -ST 8 , the central openings  40  providing clearance for the motor drive shaft  23 . Mounted on the disk in a circle about the periphery of the disk are eight photo-transistors, Q 1 -Q 8 , each transistor occupying a sector of the disk corresponding with one of the eight periods, P 1 -P 8 , respectively, of FIGS.  4 A- 4 D at a location just clockwise of the counter-clockwise edge of each period. 
     Light source plate  42  is identical with sensor plate  41  except that, in place of the eight transistors of the sensor plate, the light source plate has eight light-emitting diodes (LEDs). In the mounted positions of sensor plate  41  and light source plate  42 , the eight LEDs, D 1 -D 8 , are aligned, respectively, with the eight photo-transistors, Q 1 -Q 8  of sensor plate  41 . 
     Revolving shield  43  comprises a metal disk approximately the same diameter as sensor plate  41  and light source plate  42 . A 45 degree window  44  is cut into the outer edge of the disk. 
     Sensor plate  41  and light source plate  42  are mounted in close alignment with each other, the photo-transistors facing the corresponding LEDs so that with no opaque intervening shield the photo-transistors will be turned on. The two plates  41  and  42  are spaced just far enough apart to allow clearance for the revolving shield  32  to be mounted in between. 
     Shield  43  is secured to the motor drive shaft  23  angularly referenced with respect to rotor leg R 1  such that the arrow  45  shown in FIG. 6 is aligned with arrow  37  of FIGS.  4 A- 4 D. In the rotational position of shield  43  shown in FIG. 6 with the rotor and shield rotating in the clockwise direction the leading edge  46  of window  44  has just uncovered D 1  turning on photo-transistor Q 1  and signaling the entry of rotor leg R 1  into period P 1  (note the broken line reflection  44 ′ of window  44  on light source plate  42 ). With another 45 degrees or rotation, the trailing edge  47  of window  44  will cover diode D 1  to signal the end of period P 1  as the leading edge  46  uncovers diode D 2  to signal the beginning of period P 2 . 
     The block diagram of FIG. 7 illustrates the sequencing and control system  48  employed for the operation of motor  10 . The functional blocks of system  48  comprise a d-c source  49 , a voltage control means  51 , positioning sensor  39  and sequence and control network  52 . 
     The d-c source  49  might be rectified a-c from a utility power line or in the case of portable or mobile applications it might be a battery or a bank of batteries. In the latter case, recharging means might be incorporated. 
     Voltage control means  51  will typically include efficient means for controlling the amplitude of the voltage supplied to the motor  10 . Various types of d-c to d-c converters including time ratio control circuits and reasonant converters are commonly employed for this purpose. For applications such as the electric automobile, the control means  51  would be responsive to the accelerator pedal of the automobile. 
     The position sensor  39  is preferably of the type already described as shown in FIG.  6 . Its several output signals  53  supply a continuous indication of the instant location of the rotor, identifying the particular period in which rotor leg R 1  operating (i.e. one of the periods, P 1 -P 8  of FIGS.  4 A- 4 D). 
     The sequence and control network  52  responds to the signals  53  from position sensor  39 , supplying stator and rotor drive voltages (excitation voltages) to the motor  10  as called for during each operating period in accordance with the table of FIG.  5 . The network  52  may also incorporate means for motor start-up as well as directional control means (clockwise or counter-clockwise). A micro-processor might be employed for this purpose. 
     A preferred embodiment of the d-c motor of the invention together with associated power and control means has now been disclosed in accordance with the stated objects of the invention, and while the preferred embodiment has been described as comprising a specific number of rotor and stator assemblies, various other motor configurations are considered to embody the principles and teachings of the invention. 
     FIGS.  1 - 3  and  4 A- 4 D disclose as the first embodiment a motor  10  comprising two rotors  11 ,  11 ′, each having two pairs of rotor poles interacting with eight stator poles. 
     FIGS. 8 and 9 disclose as a second embodiment a motor  55  preferably comprising three rotor assemblies  56 , each rotor assembly having three pairs of rotor legs or poles  57  interacting with twelve stator poles  58 . As in the case of the first embodiment, the twelve stator poles encircle the rotor with all twelve poles polarized as north poles. Each pair of rotor poles comprises a north pole and a south pole spaced 30 degrees or less apart, the three pairs of rotor poles being uniformly spaced about the drive shaft  59 . 
     The stator poles  58  which interact with the three rotor assemblies are energized by twelve stator assemblies  61  of the type shown in FIG. 9, each assembly comprising an elongated magnetic core  62  with like poles  58  and  58 ′ at the ends and an oppositely polarized pole  58 ″ at the center. An excitation winding  63  is positioned on each side of the central pole. Adjacent stator poles lengthwise of the motor shaft are oppositely polarized from that shown in FIG.  8 . In the motor assembly, the stator assemblies  61  are positioned longitudinally in parallel with the drive shaft each providing a stator pole  58  for each of the rotor assemblies  56 . 
     Yet another embodiment of the invention is shown in FIG. 10 in the form of a motor  65  comprising four rotor assemblies,  66  each having four pairs of rotor legs  67 . The two legs  67  of each pair are spaced 22.5 degrees or less apart and the three pairs of rotor legs are uniformly spaced about the drive shaft  68 . The four pairs of rotor legs are again alternately polarized, north and south, and the eight poles of each rotor assembly interact with sixteen stator poles  69  which encircle the rotor assembly. As in the case of the first and second embodiments the stators which interact with a given rotor are all of the same polarization while adjacent rotor poles and associated stator poles lengthwise of the motor shaft are oppositely polarized. 
     As indicated in FIG. 11, the stator care for motor  65  of FIG. 10 serves all four rotors of motor  10  with its four stator poles  69 ,  69 ′,  69 ″ and  69 ′″ aligned longitudinally of motor  65  and its drive shaft  68 . Also as shown, the corresponding poles of successive rotors are alternately polarized, north, south, north south. Excitation is provided by means of excitation windings  71  positioned between adjacent poles (i.e. between poles  69  and  69 ′, between  69 ′ and  69 ″ and between  69 ″ and  69 ′″). Polarization of the windings  71  is indicated by the polarity indicators (+ and −). The three windings will all be turned on or off together and may therefore be connected in series or in parallel as appropriate for the given design. 
     The three embodiments of the invention as described herein define motor assemblies having twice as many stator poles as rotor poles. Additional variations of these embodiments ae considered to fall within the scope of the invention, such variations incorporating equal numbers of rotor and stator poles. For such embodiments of the invention, the sequencing and control systems would be essentially the same as described for the first embodiment but there would be no inactive stator poles during the energized periods of rotor and stator poles. 
     The three embodiments of the invention described thus far include a two-rotor version, a three-rotor version and four-rotor version. Yet another version is contemplated which employs only single rotor assembly and a surrounding ring of stator poles. The rotor assembly in this embodiment might be any one of the three rotor assemblies of FIGS. 1,  8  or  10 . A magnetic disc would replace the second rotor assembly of the two rotor version for the closure of the stator flux paths. 
     Further extensions of these embodiments incorporating still larger numbers or rotor assemblies, each with additional numbers of rotor pairs are possible. 
     It will now be recognized that a new and different motor design is provided in accordance with the stated objects of the invention, and although but a few embodiments of the invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.