Abstract:
A motor arrangement has an electronically commutated motor of an explosion-protected design with a permanent-magnetic rotor, a stator, and an electronic commutation device. At least one galvanomagnetic rotor position sensor is arranged on the stator and separated from the permanent-magnetic rotor by an air gap, wherein the at least one galvanomagnetic rotor position sensor is configured to detect a magnetic field of said permanent-magnetic rotor and emits an output signal controlling said electronic commutation device. An opto-coupler transmits the output signal of the at least one galvanomagnetic rotor position sensor to the electronic commutation device. A current supply in the form of an ac system or a three-phase system supplies current to the at least one galvanomagnetic rotor position sensor. An isolating transformer is interconnected between the at least one galvanomagnetic rotor position sensor and the current supply.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a motor arrangement with an electronically commutated electric motor of an explosion-protected configuration, as they can be found, for example, in applications for driving fans in a potentially explosive atmosphere.  
           [0003]    2. Description of the Related Art  
           [0004]    In such motor arrangements, so-called safety barriers are conventionally used which, however, are too expensive for most applications. Also, voltage drops that are too high can occur for such safety barriers.  
         SUMMARY OF THE INVENTION  
         [0005]    It is an object of the present invention to provide a new motor arrangement whose motor is suitable for operation in a potentially explosive environment.  
           [0006]    In accordance with the present invention, this is achieved in that on the stator of the electric motor, and separated from the permanent magnetic motor by an air gap, at least one galvanomagnetic rotor position sensor is provided for detecting a magnetic field of the permanent magnetic motor whose output signal serves for controlling an electronic commutation device; the current supply of the galvanomagnetic rotor position sensor is realized by an alternating-current (ac) or three-phase current supply system with interconnection of an isolation transformer; and the output signal of the galvanomagnetic sensor is supplied via an opto-coupler to the electronic commutation device.  
           [0007]    In a motor arrangement according to the invention an electric motor with a galvanomagnetic sensor is thus used. Between the motor circuit and the sensor circuit a complete electrical isolation is provided by which it is reliably prevented that in a failure situation energy-rich mains voltage can reach the sensor circuit. The actual electronic commutation device of the motor arrangement is preferably arranged external to the electric motor. This makes it possible to electrically separate (isolate) the sensor circuit completely from the coil circuit of the electric motor, for example, on a relatively small printed circuit board mounted within the electric motor. Since the output signal of the sensor is supplied by an opto-coupler to the electronic commutation device, a complete electrical isolation is possible also in this context. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0008]    In the drawing:  
         [0009]    [0009]FIG. 1 is a schematic illustration of a preferred embodiment of the motor arrangement of the invention; and  
         [0010]    [0010]FIG. 2 is a preferred embodiment of an electronically commutated electric motor for use in an arrangement according to FIG. 1. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0011]    In the following description same parts or same-acting parts are referenced with identical reference numerals and are usually described only once.  
         [0012]    [0012]FIG. 1 shows schematically an embodiment of the motor arrangement  11  according to the invention. To the right, an electronically commutated electric motor (ECM)  10  with a stator coil  12 , a permanent-magnetic rotor  14 , and a printed circuit board  16 , which is arranged within the ECM  10  in an insulated way and on which a Hall IC (integrated circuit)  18  is arranged which is controlled by a magnetic field of the rotor  14 , are located. The parts  12 ,  14 ,  16 ,  18 ,  20  are illustrated only schematically in order to facilitate understanding of the invention. For example, four-pole or six-pole rotors  14  are used in practice.  
         [0013]    The printed circuit board  16  supports also an opto-coupler  20 , a fuse  21 , a resistor  22 , two Zener diodes  23 , and a resistor  24 . It is supplied with direct current (dc) of 10 V via two lines  26 ,  28  by a rectifier  30  which is arranged on an external printed circuit board  32  on which also the electronic commutation device  34  is arranged to which the coil  12  is connected. This printed circuit board  32  is preferably located external to the ECM  10 , conventionally in an explosion-protected housing (pressure-proof housing). The electronic commutation device  34  comprises preferably an electronic limiter for the motor current, as is known, for example, from EP-A2-0739084. The negative line  28  is provided twice in order to provide redundancy.  
         [0014]    The printed circuit board  32  is connected in operation by terminals  36 ,  38  to an alternating current source  40 , typically to an alternating current supply system with 230 V, 50 Hz, or to a three-phase supply system. This alternating current is rectified by a rectifier  44  (with an electronic smoothing device, i.e., capacitors and the like) and supplied by a direct-current intermediate circuit  45 ,  47  to the electronic commutation device  34 . The voltage at the direct-current intermediate circuit  45 ,  47 , depending on the type of motor, can be, for example, between 20 V and more than 350 V.  
         [0015]    The signals at the output of the opto-coupler  20  are guided via two lines  46 ,  48  to the electronic commutation device  34  and control in a conventional way the commutation as a function of the position of the rotor  14 .  
         [0016]    The primary coil  50  of a short-circuit-proof isolation transformer  52  (preferably corresponding to EN 50020, section 8.1) is connected to the terminals  36 ,  38 , and the rectifier  30 , which supplies the Hall IC  18  and the opto-coupler  20 , is connected to the secondary coil  54 .  
         [0017]    The positive line  26  is connected via the fuse  21  (for example, 62 mA, 125 V) and a junction  25  with the anode of the LED  58  of the opto-coupler  20  whose cathode is connected by a resistor  22  with the signal output of the Hall IC  18 . Moreover, the junction  25  is connected via the resistor  24  with the supply input of the Hall IC  18 . The negative line  28  is connected with the negative terminal of the Hall IC  18 . Between the junction  25  and the negative line  28  the two Zener diodes  23  are positioned, for example, configured for 5.6 V. This ensures that the voltage in the intrinsically safe circuit cannot become greater than 5.6 V. In a failure situation, the fuse  21  is triggered. The series resistor for the Zener diodes  23  is located at the output of the rectifier  30  on the external printed circuit board  32 .  
         [0018]    The resistors  22  and  24  (for example, each 1 kΩ) are dimensioned such that for a short circuit the maximum electric power generated thereat is significantly lower than two-thirds of the maximum allowable power loss of these resistors.  
         [0019]    Reference numeral  60  symbolizes the electrical isolation between the intrinsically safe sensor circuit (below the line  60 ) and the energy-rich motor circuit (above the separation line  60 ). This isolation is formed by the isolation transformer  52 , the opto-coupler  20 , and partially also by an insulation  62  which is arranged in the air gap  63  between the Hall IC  18  and the rotor  14 . The insulation  62  is only symbolically illustrated in FIG. 1. It is illustrated in FIG. 2 by means of a preferred example. Preferably, it is provided on the stator. However, it is also possible to provide a corresponding insulation on the rotor  14 .  
         [0020]    In this context, the following should be noted: for an intrinsically safe electric motor relatively large insulation thicknesses are prescribed by the standard which, for smaller motors and especially for electronically commutated motors, cannot be complied with because the motor would not be functioning any longer. For example, according to the standard, an insulation layer at the location  63  must have a thickness of at least 3 mm but in this case the Hall IC  18  could no longer be controlled by the magnetic field of the rotor  14 .  
         [0021]    A complete electrical isolation of the printed circuit board  16  from the electrical supply system  40  is achieved by the isolation transformer  52  and the opto-coupler  20  so that the intrinsic safety is also provided when the insulation  62  does not have the prescribed thickness. One can see easily that even an insulation layer  62  of a reduced thickness contributes in this case additionally to the intrinsic safety.  
         [0022]    [0022]FIG. 2 shows a preferred embodiment of the ECM  10  of FIG. 1, here in the form of an external-rotor motor  10 . It has a base part  17  which is formed as a monolithic part of the bearing support tube  72  in which two ball bearings  74 ,  76  are provided which support a shaft  78  on whose upper end a rotor cup  80  is fastened. A spring  82  generates an initial tension between the upper ball bearing  74  and the rotor cup  80  as well as between the inner rings of the two ball bearings. At the lower end of the shaft  78  a spring ring  84  is provided. The base part  70  and the bearing support tube  72  can also be manufactured of a suitable plastic material or, for example, of diecast aluminum with a magnesium contents of less than 6%.  
         [0023]    The rotor cup  80  is comprised, like the base part  70 , preferably of a suitable plastic material with embedded carbon fibers in order to prevent static electricity from being generated on the surface of the plastic. The surface resistance is preferably below 10 9  Ω, especially preferred in the range of approximately 10 5  Ω to approximately 10 9  Ω. Preferably, a plastic material is used which is resistant to a short-term exposure to flames.  
         [0024]    The rotor cup  80  supports fan vanes  86  on its external side and is formed with them as a monolithic part. It widens conically in the downward direction to a so-called skirt  88  which cooperates with a stationary part  89  that, as illustrated, projects into this skirt  88  and in this way prevents that foreign bodies can reach the interior of electric motor  10 . The flow direction of the air is illustrated by  91 , i.e., it flows from the top to the bottom, so that in the area of the opening  87  of the skirt  88  a suction effect is generated which counteracts the introduction of foreign bodies.  
         [0025]    In the interior of the rotor cup  80  a cup-shaped part  90  of a material of soft ferromagnetic properties is fastened by means of plastic rivets  92 , and the permanent-magnetic rotor  14 , preferably a so-called rubber-bonded magnet which is comprised of a mixture of rubber-like substances and suitable hard ferrites, is fastened on the inner side of the part  90 . This has the advantage in comparison to a hard permanent magnet that no friction sparks can be generated when friction occurs between the stator  100  and the permanent-magnetic rotor  14 .  
         [0026]    In the radial space between the permanent magnet of the rotor  14  and the bearing support tube  72  the stator of the electric motor  10  is positioned, comprising: a stator laminate pack  100 , which is pressed onto the external side of the bearing support tube  72 , a two-part coil body  102 ,  104 , and a stator coil  12 . (The embodiment shows a single-phase ECM  10  with a single coil  12 . It is operated by a two-pulse system, compare, for example, DE 23 46 380, where a corresponding electric motor is described. The invention is suitable naturally in the same way for motors with more than one phase and with more than two current pulses per rotor rotation of 360 electrical degrees.) Below the stator laminate pack  100  and the stator coil  12 , the printed circuit board  16  with the Hall IC  18  is located. This printed circuit board  16 , like the stator laminate pack  100  and the coil  12 , is completely embedded in a very low-conductivity potting compound  110  which also preferably completely encloses the Hall IC  18 , the latter being arranged approximately opposite the lower end  112  of the permanent-magnetic rotor  14 , i.e., in its stray flux area. In the area of the coil  12  and the other current-carrying parts with energy-rich currents, the potting compound  110  has a thickness of at least 3 mm.  
         [0027]    The potting compound  1   10  serves not only for insulating the coil  12  and the electronic device but also for dissipating electrostatic charges. For this reason, it is of low conductivity. Its surface resistance is preferably in the range of 10 5  Ω to 10 9  Ω. In practice, occasionally values of 10 3  Ω may occur. The surface resistance should not be too low so that no disturbing currents flow from the coil  12  to the Hall IC  18  which would disturb the Hall signal. A resistance gradient in the sense that the specific resistivity of the insulation on the surface is lower than in the interior of the insulation is optimal.  
         [0028]    In this way, the low-conductivity insulation layer  62  described in connection with FIG. 1 is positioned also between the permanent-magnetic rotor or rotor magnet  14  and the Hall IC  18  and provides a good electrical isolation  60  between the ECM  10  and the sensor circuit and is thus very advantageous for the so-called intrinsic safety of the electric motor  10 .  
         [0029]    With respect to the details of embedding the stator with the plastic material, in order to be brief, reference is being had to U.S. Pat. No. 5,973,424 wherein a suitable method and suitable materials are described in detail.  
         [0030]    The coil  12  is connected via terminals  114  on the printed circuit board  16  with the lines  46 ,  48  which lead to the electronic commutation device  34 .  
         [0031]    The potting material  1   10  extends preferably also through the air gap  120  of the electric motor  10  and covers the air gap side of the stator laminate pack  100  completely; compare U.S. Pat. No. 5,973,424.  
         [0032]    An intrinsic safety ECM  10  is obtained in this way whose electronic commutation device  34  is preferably arranged external to the electric motor  10  and must not be intrinsically safe because between it and the electronic sensor circuit (on the printed circuit board  16 ) a strict electrical isolation  60  is provided. The printed circuit board  32  can be conventionally arranged in an explosion-protected housing external to the ECM  10 . A preferred arrangement of such ECM  10  is a so-called tube fan, i.e., a fan which is mounted in the tube of a venting device in which explosive media may be present.  
         [0033]    If needed, at the locations A, B (FIG. 1) between the electrical supply system  40  and the rectifier  44  an isolation transformer (analog to the transformer  52 ) can be provided which electrically isolates the electronic commutation device  34  from the electrical supply system  40 . This makes possible a lower voltage for the intermediate circuit between the lines  45 ,  47 , for example, 20 V. In addition, many variations and modifications are possible without leaving the gist of the invention.  
         [0034]    While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.