Abstract:
An electromagnetic rotor machine ( 10 ) of the hypocycloid type comprising a machine housing ( 12 ), an annular stator ( 30 ) in the machine housing an annular rotor ( 50 ) of a magnetic material, which is supported orbiting and rotationally around it&#39;s own axis in the machine housing, and at an interior side thereof adapted to operatively engage a drive element supported in the machine housing. The stator ( 30 ) comprises circumferentially arranged electromagnets which are magnetically separated from each other, each of said magnets comprising a core ( 34 ) and a coil ( 36 ) and being arranged in such a number that a plurality of magnets always is located at a side of the rotor ( 50 ).

Description:
TECHNICAL AREA 
       [0001]    The present invention relates to an electromagnetic rotor machine of the hypocycloid type. Such machines are known, for example from U.S. Pat. Nos. 2,761,079, 3,560,774, 4,482,828 and 5,703,422. 
       BACKGROUND 
       [0002]    For example, electrical fork lift trucks are normally powered by conventional DC motors. The development of power electronics has made asynchronous motors more common. The torque requirements are so high that the power train includes a gear transmission. Other types of motors such as servo motors magnetized by permanent magnets and SR (Switched Reluctance) motors have also been tested. Applications using direct drives without any transmission between motor and driving wheels can also be found. As the torque of the motor and its radius are directly related, the motor will have a large diameter and a high cost. In systems having a fixed transmission ratio, the maximum speed is limited by the physical limits for the motor speed. In DC drives the power electronics also set limitations on the frequency that can be used. The losses increase with higher frequences. 
       SUMMARY OF THE INVENTION 
       [0003]    An object of the present invention is to develop further a rotor machine of the above defined type, in order that its inherent advantages of a high torque and a compact construction may be utilized, particularly when it is used as a motor 
         [0004]    This object is obtained by the features defined in the appended claims. 
         [0005]    In an aspect of the invention the rotor is an annular rotor made of a magnetic material and supported orbiting and rotationally around its own axis in the machine housing and at an interior side thereof adapted to operatively engage a drive element supported in the machine housing. Thereby the rotor can be distinctively guided in an orbit close to the stator in the machine housing to securely and uniformly interact with the drive element and the stator. 
         [0006]    The stator further comprises circumferentially arranged electromagnets which are magnetically separated from each other, each of said magnets comprising a core and a coil and being arranged in such a number that a plurality of magnets always is located at an arbitrary side of the rotor. By “a side of the rotor” is here intended to be construed approximately as a half circumference of the rotor projected in a direction. Thereby the rotor can cooperate with a plurality of magnets at a time, so that for example when the machine is a motor, then one or more electromagnets can optionally attract the rotor depending on the current need for torque. Using a suitable control, the motor should then be capable of having better low speed characteristics and thereby a relatively large speed variation which is particularly important when it is used for vehicle propulsion purposes. 
         [0007]    The magnet coils are in an embodiment oriented so that their windings lie in planes parallel to the longitudinal axis of the machine. i.e. the coils extend approximately tangentially or in a direction transversely to the longitudinal axis. In an advantageous manner, the poles of the magnets may be arranged in a tangential direction in the stator. 
         [0008]    According to an embodiment of the invention, the rotor is in rolling engagement in the machine housing and the drive element is a collar-shaped carrier capable of transmitting rotational movement from the rotor to a shaft concentrically journalled in the machine housing. Obtained is thereby a very compact and efficient power transmission between the rotor and the shaft. The one end of the carrier is then suitably connected to an axial end of the rotor and its other end is connected to the shaft. The carrier will then perform a conical orbiting movement about the shaft. In addition to propulsion of vehicles, a rotor machine according the invention arranged as a motor can be used as a servomotor, for example for actuators and industrial robots. 
         [0009]    The rotor machine can also have means for engaging and disengaging the carrier respectively to and from the shaft. 
         [0010]    If the shaft has a drive means adapted to be brought into and out of engagement with one of the above mentioned rotatable bearing holders to be rotated in engagement with the bearing holder, a gearshift position can be obtained where the shaft is brought to rotate in the machine housing with the same angular speed as the orbiting speed of the rotor about the machine center. This solution can be convenient for propelling vehicles of different kinds. 
         [0011]    Other objects, features and advantages of the invention is apparent from the claims and the following detailed description of exemplary embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0012]      FIG. 1  shows a rotor machine according to the invention; 
           [0013]      FIG. 2  shows a rotor machine with portions cut away; 
           [0014]      FIG. 3  is a longitudinal section view of a rotor machine according to  FIG. 1  with a disengaged shaft; 
           [0015]      FIG. 4  is a longitudinal section view of a rotor machine according to  FIG. 1  with a shaft engaged in one of two gear shift positions; 
           [0016]      FIG. 5  is a cross-sectional view along line  5 - 5  of  FIG. 3 ; 
           [0017]      FIG. 6  is an end view, partly in section, showing a stator and a rotor in a rotor machine according to the invention; 
           [0018]      FIG. 7  shows, with portions broken away, an isolated rotor and a carrier for a rotor machine according to the invention; 
           [0019]      FIG. 8  diagrammatically shows paths of movement of a rotor in a machine according to the invention; and 
           [0020]      FIGS. 9 and 10  is a view, partly in section, of two alternatively designed rotor machines according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0021]    The embodiment of the rotor machine  10  shown in  FIG. 1  comprises a machine housing  12  having an inner pair of machine covers or end plates  14 ,  16  and outer pair end plates  18 ,  20  connected together by a plurality of bolt assemblies  22 . An annular stator  30  is supported between the end plates  14 ,  16 . 
         [0022]    The machine has a rotor  50  adapted to perform an orbiting motion inside the machine housing  12 . 
         [0023]    While the machine  10  may be arranged as a pure generator, in the examples shown it is supposed to be arranged as a motor  10 . By a control system (not shown) the motor  10  can also have a generator function, for example for the recovery of brake energy. 
         [0024]    As is apparent for example from  FIG. 6 , the annular stator  30  is provided in the shape of a plurality (twelve) of electromagnets  32  distributed around the periphery and each consisting of a core  34  and a coil  36 , while the rotor is made of a magnetic material. The magnets  32  are magnetically separated from each other by gaps  38  that can be filled by a non-magnetic material. All cores  34  and filled gaps  38  may then be fabricated in a single annular piece by a co-molding method of a type known as such. It should also be possible to fabricate the annular stator  30  including the filled gaps  38  the so-called PIM (Powder Injection Molding) method and also by powder metallurgical methods. 
         [0025]    As is apparent from the circumscribed and enlarged area of  FIG. 6 , the windings of the coils  36  of the electromagnets  32  are oriented in planes substantially parallel to the longitudinal axis of the rotor machine. 
         [0026]    The effective radially inner portion of the core  34  is U-shaped in cross-section. The radially outer U-shaped outer cross-section has no magnetic function but only serves to structurally retain the coil  36  in place in the core  34  and the magnet  32  itself in the machine housing  12 . 
         [0027]    The electromagnets  32  can be fed by direct current although alternating current operation is functions in a corresponding way. AC operation may, however, be more difficult to control and may need certain measures to limit the iron losses (sddy current and hysteresis losses). 
         [0028]    An energized magnet  32  will influence neighboring magnets by its leak flux. The magnitude of this influence depends inter alia on the distance between the magnets  32 , i.e. the thickness of the air gap or the non-magnetic material  38 . The fact that a portion of the flux travels through a neighboring, not energized magnet is a limited drawback as this will give a larger pole area having substantially the intended force direction. By letting the direction of the current flow be mutually opposite adjacent for adjacent coils  36 , adjacent magnets  32  can be energized simultaneously by having the direction of the current flow in adjacent legs being the same (parallel). 
         [0029]    A suitable connection method may be pulse connection: ON or OFF with full voltage and controlling the connection time of the ON pulse (PWM—Pulse Width Modulation). The most simple manner is to connect the respective coil  36  to a pulse a each energizing instance and having the connection time adapted to the actual need of torque/power, but in order to obtain a smooth or constant force and torque it may be convenient to energize the coil  36  by a plurality of shorter connection pulses. By such a digital ON/OFF connection operation, the power losses that otherwise appears in semiconductors with analog control can be avoided. 
         [0030]    The driving torque on the rotor  50  is obtained by the force that is generated when a magnet  32  in a favorable position is energized by a current pulse from its coil  36  that generates a magnetic flux and pulls the rotor  50 , being the armature, towards the pole faces  40  of the magnet core  34  ( FIG. 6 ). The angle α between the contact point of the rotor  50  and the magnet  32  being energized may ideally be about 90 degrees. In operation, a suitable angle α and the duration of the current pulse can be varied by the control system (not shown) of the motor if many magnets are to be working together. In order to get the best possible efficiency, it may be suitable to redirect the energy of the magnets, possibly in connection with an increase of the voltage level (not shown). The angle which is most suitable depends on many factors such as speed or lead and what has been preferenced, such as efficiency/minimizing losses or high torque/high power. As far the torque is sufficient, it may be convenient to operate with a smaller angle. As mentioned above, if the need for torque is high, many adjacent magnets can be connected together at a time. 
         [0031]    The control system can also comprise position sensors, for example formed integrally with the roller bearings  62  to be later described for the rotor. Such position sensors, which can be known Hall-type sensors, are capable of continuously signalling the position of the rotor  50  in the motor  10  to the control system. The position of the rotor  50  may however also be sensed by continuously measuring the impedance of the coils as a function of the position of the rotor in the stator. More specifically, the impedance varies with the magnitude of the air gap between the rotor  50  and the respective coil  36 . Thereby the corresponding control system can operate completely without any discrete sensor. This solution may be attractive as sensors are expensive. 
         [0032]    The rotor  50  is excentrically journalled in the machine  10  by two journal bearing assemblies  60 ,  60  capable of guiding the rotor to perform an orbiting motion in there machine housing  12  with a narrow gap to the electromagnets  32 . 
         [0033]    In the embodiment shown (compare  FIG. 2-4 ) each bearing assembly  60 ,  60  comprises a roller bearing  62  centrally arranged in the machine housing  12 , the inner ring of each bearing supporting a centric annular flange of an eccentric bearing holder  64 , the eccentric annular flange of which in turn supports a roller bearing  66  for the rotor. When the rotor  50  is orbiting in the machine housing  12 , its axis center C ( FIG. 6 ), guided by the bearing assemblies  60 ,  60 , will perform a rotational movement along a circle having a radius corresponding to the eccentricity e of the rotor  50 . 
         [0034]    In one embodiment of the invention the rotor machine  10  has a rotationally supported central shaft  80 . As is apparent from  FIG. 2 , the shaft  80  is rotationally supported by roller bearings  24 ,  26  in the end plates  18 ,  20 . The shaft  80  is in rotational driving engagement with the rotor  50  via a carrier or a carrier sleeve  70 . More precisely, the respective ends of the carrier sleeve  70  are connected on the one hand with the shaft  80  and on the other hand with the rotor  50  via drive elements  72  received in pairs of elongated openings  74  (see also  FIG. 7 ) which, like a universal coupling, allow the carrier sleeve  70  to perform limited oscillating movements in planes containing the axis of the shaft  80 . 
         [0035]    For the rotor  50  not to rotate freely about its own axis when it orbits the shaft  80  in the machine housing  12 , but be capable of being connected to the shaft  80  in a gear relation for transmitting torque therebetween, the rotor is in rolling engagement with the machine housing  12 . As is most clearly apparent from  FIGS. 4 and 5 , the rotor  50  is, via internal gear paths  52  at the outside of rotor  50 , in gear engagement with internal gear paths  54  of the end caps  14 ,  16 . 
         [0036]    When the rotor rolls eccentric in the machine housing  12 , the carrier sleeve  70  will perform a conical orbiting motion around the shaft  80 . For the transmission to be free of play which is important for example in robot operation, the drive elements  70  can be prestressed in the openings  74 . Instead of the cylindric shape shown, the drive elements  72  can also have a spherical shape. Other solutions to connect the carrier sleeve  70  rotationally rigid and tiltably between the rotor  50  and the shaft  80  can, for example, include spherical spline joints (not shown). 
         [0037]    Thus, when the rotor  50  is rolling in the direction R ( FIG. 8 ) in the machine housing  12 , a point P of the rotor  50  will move along an arc of a hypocycloid for each revolution of the rolling rotor in the housing. The size of the arc depends on the difference between the inner radius of the machine housing and the outer radius of the rotor. 
         [0038]    With a difference in radii of for example 5%, there is obtained a reduction ratio of 1:20, i.e. for each revolution of the rotor  50  in the machine housing, the shaft  80  will turn 18 degrees. 
         [0039]    According to the modification shown in  FIGS. 3 and 4  of the embodiment of  FIG. 2 , the rotor machine has a two-shift transmission so that in addition to the gearshift position described above when the shaft rotates with the angular speed of a point of the rotor  50 , the rotor machine also has a gearshift position where the shaft  80  rotates with the rolling rpm of the rotor  50  or the angular velocity of the center of the rotor  50 , as well as a neutral position therebetween. 
         [0040]    As is more closely apparent from  FIGS. 3 and 4 , the shaft  80  is provided with a gearshift mechanism  90  comprising a gear shift means  92  which is axially slidable between three positions. In the vicinity of the forward, in  FIG. 3  the left, end of the carrier sleeve  70 , the shift means  92  has a plurality of radially inward and outward movable drive elements  94 , instead of the stationary drive elements  72  of  FIG. 2 . Drive elements  94  have a radially inner narrowed neck portion  96  engaging guiding flanges  98  of the gear shift means  92  so that the drive elements  94  are pulled back inwards when the shift means  92  is pushed into shaft  80 , and are pushed forward when the shift means  92  is pushed out of the shaft  80 . Thus, when the drive elements  94  are retracted, the shaft  80  is disengaged from the carrier sleeve  70  and vice versa. 
         [0041]    In the position according to  FIG. 3  the shift means  92  is depressed only halfway into the shaft  80 . The shaft  80  is then fully disengaged from the carrier sleeve  70  and the rotor  50 . 
         [0042]    At its rear end the shift means  92  has a transversely oriented drive means  100  that is out of engagement with the right-hand bearing holder  64 . In the gearshift position according to  FIG. 4 , the drive means  100  is, however, depressed into a recess  102  to engagement with the right-hand bearing holder  64 . When the bearing holder  64  rotates with the angular velocity of the rotor  50  about its rotational center, the drive means  100  will drive the shaft  80  with said angular velocity by engagement with the walls in a slot  104  of the shaft  80 . In this second shift position the shaft  80  is driven in the opposite direction compared to when it is driven by the rotor  50  via the carrier sleeve  70 . To utilize both shift positions as forward shift positions when the motor drives a vehicle (not shown), the driving direction of the electromagnets  32  can be reversed in connection with shifting between the both positions. 
         [0043]      FIGS. 9 and 10  show two modifications of a rotor machine  10  according to the invention. More precisely,  FIG. 9  shows a rotor machine arranged as a linear actuator, and  FIG. 10  shows a rotor machine arranged as a crankshaft assembly. In these embodiments the rotor  50  needs not be in rolling engagement with the machine housing  12  but can advantageously be allowed to orbit without any rotation of its own in the machine housing  12  (not shown). 
         [0044]    In the embodiment according to  FIG. 9  the rotor  50  has internal tangential rifles and groves  54  that engage a helical thread  112  of a driving rod  110  slidably supported in a machine housing  12 . When the rotor  50  performs its orbiting movement within the stator in the machine housing  12 , it will displace the driving rod  110  in a desired actual direction through the machine housing  12 . In order that the driving rod  110  should not rotate in the machine housing  12 , it can be non-rotatably guided in the housing, for example by having a non-circular cross section (not shown) or by the ends of the driving rood  110  being non-rotatably connected to the object to be moved by the linear actuator  10  (not shown). 
         [0045]    In the embodiment according to  FIG. 10  the rotor  50  has an internally freely rotatably supported shaft  130 . The bearing is provided by a pair of opposite roller bearings  132  (only one is shown in  FIG. 10 ). If the rotor machine functions as a motor, the opposite ends of shaft  130  will orbit as crank pins of a crankshaft. This crankshaft movement maybe utilized in many different ways, for example to obtain a forward and backward movement of a connecting rod  134  that in turn is capable of driving many different kinds of machinery, such as pumps etc. 
         [0046]    The movement of the rotor  50  in the machine housing can also be utilized to intentionally have a motor according to the invention function as a vibration generator for different applications. If the vibrations are too big in driving applications, they may be balanced by different methods for rotary machines. A simple solution may be to have the bearing holders  64  support counterweights that balance the eccentrically located rotor  50  and possibly a joining eccentrically movable components (non shown).