Abstract:
An electronically commutated motor ( 4 ) has a stator ( 14 ) with two winding phases ( 25, 26 ) which are alternatingly supplied with current during one rotor rotation through  360 ° cl. The motor also has a permanent-magnet rotor ( 28 ) which, when the motor ( 4 ) is currentless, assumes at least one predefined rotational position from which the rotor starts in a desired rotation direction upon excitation of a predefined winding phase. A bistable multivibrator ( 64 ), which is controlled by the voltage that is induced by the rotor in the instantaneously currentless winding phase, is provided for alternatingly switching on the two winding phases. The bistable multivibrator ( 64 ) has an electrical preferred position ( 92 ) that it assumes when the motor ( 4 ) is switched on, in order to supply power, during the switching-on operation, to the predefined winding phase and thereby to allow the rotor to start in the desired rotation direction. The motor current can be temporarily increased at startup in order to increase the torque at startup.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to an electronically commutated direct-current motor (ECM).  
         BACKGROUND  
         [0002]    Motors of this kind are used, inter alia, to drive miniature fans (cf. EP-A1-0 908 630 and corresponding U.S. Pat. No. 6,013,966, FEHRENBACHER et al). For various reasons, it may be desirable to operate such a motor without a Hall generator, and for that purpose to commutate it with the voltage that is induced, during operation, by the rotor in the stator winding. This is known, for example, from U.S. Pat. No. 4,156,168. VOGEL, but in the case of this known motor the direction in which it will start after being switched on is not certain, and this known motor is therefore suitable only for specific applications in which rotation direction is not important.  
         SUMMARY OF THE INVENTION  
         [0003]    One object or the invention is therefore to provide new electronically commutated motor whose startup rotation direction is certain. In accordance with the invention, the motor used is one having a rotor that, when the motor is currentless, has at least one mechanical preferred position. The current in the motor is controlled using a bistable multivibrator that has, at startup, an electrical preferred position which is adapted to the mechanical preferred position of the rotor. At startup, the result of the electrical preferred position is that the stator is excited in such a way that the rotor starts, from its mechanical preferred position, in the correct rotation direction. Because a separate rotor position sensor is eliminated, a motor of this kind has a simple configuration with good efficiency, since the power consumption for a rotor position sensor is eliminated. The invention is therefore particularly advantageous for miniature and subminiature motors in which the power consumption of a rotor position sensor, for example a Hall TC, would greatly reduce the electrical efficiency; and it is highly suitable, for example, for motors in which the electronic components are arranged separately from the actual motor (i.e. stator with stator winding, and rotor).  
           [0004]    Further details and advantageous developments of the invention are evident from the exemplary embodiment described below and shown in the drawings, which is in no way to be understood as a limitation of the invention.  
       
    
    
     BRIEF FIGURE DESCRIPTION  
       [0005]    [0005]FIG. 1 is a longitudinal section through a fan  1  that is driven by an electronically commutated motor  4 ;  
         [0006]    [0006]FIG. 2 is a plan view at the fan of FIG. 1, viewed in the direction of arrow II of FIG. 1;  
         [0007]    [0007]FIG. 3 is a schematic circuit diagram of a motor according to the present invention;  
         [0008]    [0008]FIG. 4 shows a preferred exemplary embodiment of a circuit corresponding to FIG. 3, with further details:  
         [0009]    [0009]FIG. 5 is a graph of the voltage that occurs during operation at winding phase  25  of FIG. 4, i.e. between points  3 A and  3 B;  
         [0010]    [0010]FIG. 6 is a graph of the total current T for the arrangement shown in FIG. 4;  
         [0011]    [0011]FIG. 7 is a graph of the voltage at an output S of the circuit of FIG. 4 when the motor is rotating; and  
         [0012]    [0012]FIG. 8 is a graph of the voltage at output S of FIG. 4 when rotor  6  is jammed or blocked from rotating.  
     
    
     DETAILED DESCRIPTION  
       [0013]    [0013]FIGS. 1 and 2 show, purely by way of example, a radial fan  1  as known from U.S. Pat. No. 6,013,966. This has a fan wheel  2  and an electronically commutated external-rotor claw polo motor  4  which directly drives fan wheel  2 . Motor  4  has a permanent magnet external rotor  6 . As shown in FIG. 2, two diametrically opposite positioning magnets  8  are provided, when motor  4  is at a standstill, these rotate rotor  6  into a preferred position (also called the “starting position”) from which it can easily start up. Magnets  8  are arranged in pocket  12  of fan housing  10 .  
         [0014]    Motor  4  has a stator  14  with two opposing claw-pole pieces  18 ,  19  between which, as shown, is located an annular winding  16  on a winding body  15 . Winding  16  is wound in bifilar fashion and has two winding phases  25  and  26  which are also shown in FIGS. 3 and 4. Phase  25  has two terminals  3 A and  3 B which are shown in FIGS. 2, 3, and  4 , and phase  26  has two terminals  3 C and  3 D.  
         [0015]    Claw-pole pieces  18 ,  19  have claw poles  20  which extend in an axial direction (cf. FIG. 1). The rotor magnet is labeled  28 , and can be a so-called “rubber magnet,” i.e. a mixture of rubber and hard ferrite. It is located in a support piece  29  that is configured integrally with fan wheel  2  and in which a shaft  30  is also mounted. The latter runs in a radial plain bearing  32 , and its free end is axially braced against a thrust bearing  34 . Rotor  6  is axially offset with respect to stator  14  in order to generate a force F directed toward bearing  34 .  
         [0016]    Fan wheel  2  has radially extending fan blades  36 . An axial air intake opening is labeled  38 . Located in it is an NTC (Negative Temperature Coefficient) resistor  40  that serves an a temperature sensor and is connected to two terminals K 1  and K 6  (FIG. 2).  
         [0017]    Terminals K 1 , K 6 , and  3 A through  3 D extend axially downward in the form of elongated pine  44  whose lower ends  46  can be soldered, as shown at  49 , onto a circuit board  47  indicated with dot-dash lines. Mounts  48  for attaching fan  1  are also provided. With these mounts, the fan can ba attached, for example, to circuit board  47 .  
         [0018]    Fans of this kind are particularly suitable for use as so-called “circuit board fans,” i.e. for direct placement on a circuit board in order to cool components present thereon. Reference is made to U.S. Pat. No. 6,013,966 for further details.  
         [0019]    The electronic components B for operation of such a fan are often mounted by the customer on his own circuit board  47 , as symbolically indicated in FIG. 1, and the customer purchases only a “naked” fan  1  and installs it on his circuit board, so that an operable motor is created only by such installation. This kind of “motor manufacture” generally makes it impossible to use rotor position sensors, for example a Hall generator, which is otherwise often used in electronically commutated motors to control commutation.  
         [0020]    Since rotor magnet  28  is located, because of the effect of stationary magnets  8 , in a predefined starting position or in one of a plurality of predefined starting positions when the motor starts, a predefined winding phase of stator winding  16  must receive a starting current in a predefined direction upon switching on. The circuit shown in FIGS. 3 and 4 serves to switch on this starting current. As a result of this starting current, rotor magnet  28  is caused to rotate in the desired direction and thereby induces voltages in the two winding phases  25  and  26 ; these voltages, after suitable pulse shaping, cause commutation of the current through the two winding phases  25  and  26 . This is also known in the art as “commutation with the induced voltage.”  
         [0021]    Instead of the motor defined in U.S. Pat. No. 6,013,966, it is of course possible to use in the same fashion, for example, a motor as defined in German Utility Model DE U1 295,7 or in German Utility Model DE-U1 8 702 271.0. FIGS. 1 and 2 thus represent only a preferred exemplary embodiment whose purpose is to allow a better comprehension of the invention since, without such an example, the invention might possibly be difficult to understand.  
         [0022]    [0022]FIG. 3 is an overview circuit diagram to explain basic functions of the present invention.  
         [0023]    As show in FIG. 3, winding phase  25  is connected at its terminal  3 A to a positive line  52  that can be connected via a switch  54  to a voltage source (not shown), usually to the battery of a vehicle with a voltage between  8  and 16 V. The other terminal  3 B of winding phase  25  is connected to a first semiconductor switch  56  that in turn is connected via a node  57  and a current regulator  58  to a negative line  60  (ground).  
         [0024]    Second winding phase  26  is connected at its terminal  3 C to positive line  52 , and its terminal  3 D is connected via a second semiconductor switch  62  to node  57 .  
         [0025]    Semiconductor switches  56 ,  62  are controlled via a bistable flip-flop  64 , which during operation generates first square-wave commutation signals  66  which are fed via a delay circuit  68  to first semiconductor switch  56 , and second square-wave commutation signals  70  which are opposite in phase to first square-wave commutation signals  66  and are fed via a delay circuit  72  to second semiconductor switch  62 .  
         [0026]    The function of delay circuits  68 ,  72  is to delay the switching on and off of semiconductor switches  56  and  62 , respectively, and to make those operations less abrupt, so that motor  4  runs particularly quietly.  
         [0027]    Pulses  76 ,  78  serve to reverse flip-flop  64 . Pulses  76  are generated by an arrangement  80  which has conveyed to it, via a diode  82 , the so-called “induced voltages” or “counter-EMF” that is induced by rotor magnet  28  in the currentless winding phase  25 . Thin voltage is converted in arrangement  80  into a square-wave signal, and its edges are differentiated by a capacitor  84  and generate the pulses  76  which commutate flip flop  64  into the one direction.  
         [0028]    Pulses  78 , which are offset in time with respect to pulses  76 , are generated by an arrangement  86  which has applied to it, via a diode  88 , the voltage that is induced by rotor magnet  26  in the currentless winding phase  26 . That voltage is converted in arrangement  86  into a square-wave signal, and its edges are differentiated by a capacitor  90  and generate pulses  70  which commutate flip-flop  64  into the other direction.  
         [0029]    For starting, flip-flop  64  acquires a specific electrical position due to a starting apparatus  92 .  
         [0030]    Since the operating voltage in a motor vehicle can be, for example, between 8 and 16 V, current regulator  58  regulates motor current I (FIG. 3) to a predefined value that corresponds, for example for a specific fan  1 , to a rotation speed of 2800 RPM. Directly after switch  54  switches on, current regulator  58  is deactivated by a timer  94  for a predefined time period so that motor  4  can start up with its maximum performance.  
         [0031]    Mode of_operation (FIG. 3)  
         [0032]    At startup, constant-current regulator  58  is deactivated by timer  94  for a predefined time. e.g. for 0.5 second, so that motor  4  can start at maximum current. At the same time, switching member  92  brings flip-flop  64  into a suitable electrical position so that, for example, first semiconductor switch  56  is switched on and first winding phase  25  receives current, with the result that rotor magnet  28  begins to rotate at high acceleration in the desired rotation direction.  
         [0033]    During that rotation, an alternating voltage is induced by rotor magnet  28  in each of winding phases  25  and  26  (cf FIG. 5). The positive part of the alternating voltage in winding phase  25  is fed via diode  82  to arrangement  80 , and the positive part of the alternating voltage in winding phase  26  is fed via diode  88  to arrangement  86 .  
         [0034]    In arrangements  80 ,  86 , the relevant voltages are converted into square-wave signals, and the latter are differentiated by capacitors  84  and  90 , respectively, thereby creating pulses  76  and  78 , respectively, which switch flip-flop  64  between its bistable positions.  
         [0035]    The result is to create pulse sequences  68 ,  70  which, as rotor magnet  28  rotates, effect commutation of motor  4 , i.e. the switching on and off of semiconductor switches  56  and  62 , respectively.  
         [0036]    When motor  4  begins to reach its operating speed current regulator  58  is activated by timer  94  and controls current I to a predefined value that is independent of the operating voltage. In a motor vehicle, the latter can vary at ratio of 1:2. In the case of a defined load, e.g. when a fan is being driven, current I represents an indirect indication of the rotation speed, in other words, if current is controlled to a predefined value, then the rotation speed is thereby kept at a predefined value.  
         [0037]    [0037]FIG. 4 shows a preferred exemplary embodiment of the invention. Identical or functionally identical parts are labeled with the same reference characters as in the preceding figures, and usually are not described again.  
         [0038]    Bistable flip flop  64  contains two npn transistors  100 ,  102  whose emitters are connected to negative line  60  and whose collectors are connected via respective resistors  104  and  106  to positive line  52 . The base of transistor  100  is connected via a resistor  108  to the collector of transistor  102 , and the base of transistor  102  is connected via a resistor  110  to the collector of transistor  100 .  
         [0039]    If transistor  100  is conductive, the base of transistor  102  has a low potential and that transistor is blocked, so that transistor  100  receives a base current via resistor  108 . Because of the symmetry of the circuit, the converse is equally true, Flip-flop  64  thus has two stable states, and it can be switched back and forth between those stable states by way of electrical pulses. This switching back and forth occurs at the time of each zero crossing of the negative edges of the induced voltage.  
         [0040]    When transistor  100  is conductive, the base of npn transistor  62  (which serves as the second semiconductor switch) acquires a low potential via a resistor  112 , and that transistor is blocked. Transistor  102  is inhibited, and npn transistor  56 , which serves as the first semiconductor switch, therefore acquires—via resistor  106  and a resistor  114 —a positive potential at its base and becomes conductive, so that a current flows through winding phase  25 . That current I is regulated by current regulator  58  to an approximately constant value (cf. FIG. 6).  
         [0041]    Current I flows through a shared emitter resistor  116  of transistors  56  and  62 , and voltage U at that resistor  116  is fed via a resistor  118  to the base of an npn transistor  120 , and via a resistor  122  to the base or an npn transistor  124 . The collector of transistor  120  is connected to the base of transistor  56 , and the collector or transistor  124  to the base of transistor  62 . The emitters of transistors  120 ,  124  are connected to negative line  60 .  
         [0042]    When current I rises, transistors  120  and  124  become more conductive, so that the base current of transistor  56  or  62  that is conductive at that instant is correspondingly reduced, bringing about a decrease in current I. The latter is thereby kept at a constant value (cf. the oscillogram in FIG. 6).  
         [0043]    Each at transistors  56 ,  62  is equipped with a so-called Miller capacitor  126 ,  128  between its collector and its base. Coacting with base resistors  114  and  112 , respectively, these capacitors effect a delay in the rise and fall of current in the transistor in question, and thus make motor  4  run particularly quietly. Miller capacitors  126 ,  128  and resistors  112 ,  114  thus represent an embodiment of delay circuits  68 ,  72  of FIG. 3.  
         [0044]    The purpose of timer  94  is to deactivate current regulator  58 , for a period of, for example, 0.5 seconds after motor  4  is switched on, by bypassing current controller  58  via an npn transistor  132 .  
         [0045]    Transistor  132  is controlled by a pnp transistor  136  whose collector is connected via a resistor  134  to the base of transistor  132 , whose emitter is connected to positive line  52 , and whose base is connected via a resistor  140  to a node  142  that is connected via a resistor  144  to positive line  52  and via a capacitor  146  to negative line  60 .  
         [0046]    Capacitor  146  is discharged when motor  4  is switched on, so that transistor  136  has a negative base potential and conducts. Transistor  132  thereby receives a base current and is also conductive, so that it bypasses current regulator  58 .  
         [0047]    Capacitor  146  then charges through resistor  144 , with the result that, after about 0.5 second, the two transistors  136  and  132  are inhibited, so that current regulator  58  is activated. At this point in time, motor  4  has usually reached its operating speed.  
         [0048]    Diode  82  is connected at its anode to terminal  3 B of first winding phase  25 , and at its cathode to the emitter of a pnp transistor  150  whose base is connected to a node  152  and whose collector is connected via a resistor  154  to negative line  60  end via a resistor  156  to the base of an npn transistor  158 , whose emitter is connected to negative line  60  and whose collector is connected via a resistor  160  to positive line  52  and, via capacitor  84  (cf. FIG. 3), to the base of transistor  100 .  
         [0049]    Node  152  is connected via series circuit  164  of two diodes (e.g. BAV99) to positive line  52 , and via a resistor  166  (e.g. 51 kΩ) to negative line  60 . Node  152  thus has a potential that is more negative, by an amount equal to a substantially constant voltage, than the potential of positive line  52 . Transistors  150 ,  170  are thereby brought to their switching threshold, so that transistor  150  senses the temporally later zero crossing (at approximately 200 in FIG. 5) of the positive voltage induced in winding  25 , and transistor  170  senses the temporally later zero crossing of the positive voltage which is induced in winding  26 .  
         [0050]    Diode  88  is connected at its anode to terminal  3 D) of second winding phase  26 , and at its cathode to the emitter of a pnp transistor  170  whose base is connected to node  152  and whose collector is connected via a resistor  172  to negative line  60  and via a resistor  174  to the base of an npn transistor  176  whose emitter is connected to negative line  60  and whose collector is connected via a resistor  178  to positive line  52  and via capacitor  90  (cf. FIG. 3) to the base of transistor  102 .  
         [0051]    When transistor  56  is conductive, point  3 B has a low potential and diode  82  is blocked. When transistor  56  is inhibited by commutation, winding  25  is currentless and rotor  19  induces in winding  25  a positive voltage half-wave  202  (FIG. 5) that is more positive than the potential at node  152 , so that diode  82  becomes conductive and transistor  150  receives a base current, also becomes conductive, and in turn makes transistor  158  conductive, so that by way of capacitor  84 , transistor  100  of flip-flop  64  is kept blocked, and by way of resistor  112 , transistor  62  receives a base current and allows a current to flow through second winding phase  26 .  
         [0052]    After a rotor rotation of approximately 180° el., the potential at point  3 B drops below the potential at node  152 , so that diode  82 , transistor  150 , and transistor  158  are inhibited, i.e the voltage at the collector of transistor  158  suddenly becomes more positive, and capacitor  84  transfers that change in potential to the base of transistor  100  in flip-flop  64 , so that transistor  100  becomes conductive and consequently, via transistor  110 , transistor  102  is inhibited.  
         [0053]    The switchover of flip-flop  64  is thus brought about by the trailing edge (labeled  200  in FIG. 5) of positive portion  202  of the voltage the induced voltage U 3A-3B , which causes flip-flop  64  to switch over approximately at its zero crossing, (Rising edge  201  in FIG. 5 occurs directly after a switchover of flip-flop  64 , when the corresponding output-stage transistor  56  is inhibited.)  
         [0054]    When motor  4  is switched on, the different values of capacitors  84  (e.g. 6.8 nF) and 90 (e.g. 3.3 nF) mean that transistor  100  becomes conductive, so that at startup, winding phase  25  is always the first to receive current via its transistor  56 , and motor  4  thus starts in the correct rotation direction from its starting position that is brought about by magnets  8  in FIG. 2. Flip-flop  64  thus, when switching on occurs, acquires an electrical preferred position which is correctly associated with the starting position of rotor magnet  28 .  
         [0055]    Since transistor  100  has become conductive as a result of this switchover pulse, transistor  62  is inhibited via resistor  112 , and conversely transistor  56  is switched on via resistor  114  because transistor  102  is inhibited, so that winding phase  25  now receives current.  
         [0056]    The switching on of transistor  56  is delayed by resistor  114  and capacitor  126 , and the switching off of transistor  62  is similarly delayed by resistor  112  and capacitor  128 , so that despite the abrupt switchover of flip-flop  64 , the switching operations proceed smoothly and no unpleasant motor noise is created by rapid switching operations.  
         [0057]    Because of the symmetry of the circuit, commutation in the opposite direction, i.e. from transistor  56  (becomes inhibited) to transistor  62  (becomes conductive) does not need to be describe, since the operations occur as the inverse of the operations just described.  
         [0058]    The positive induced voltage in a currentless winding phase  25  or  26  is thus converted by the above-described circuit into a square-wave signal, and the edge at the end of that square wave causes a switchover pulse for flip-flop  64  which causes the previously currentless transistor ( 56  or  62 ) to be switched on and the previously conductive transistor ( 62  or  56 ) to be switched off. This results in secure and reliable commutation by way of the induced voltage, smooth and low-noise commutation being achieved due to the above-described delay circuit elements, despite the abrupt switchover of flip-flop  64 .  
         [0059]    An external terminal S is connected via a resistor  190  to the collector of transistor  150 . The signal at that collector, shown in FIGS. 7 and 8, indicates whether motor  4  is rotating or is jammed or blocked. If motor  4  is rotating, pulses  194  are obtained at terminal S at a frequency that is proportional to the motor rotation speed. This slate is shown in FIG. 7. If the motor is jammed, what is received at output S are pulses  196  at a very high frequency, or alternatively a zero frequency. The state with the high frequency is shown in FIG. 8. This makes it easy to monitor whether motor  4  is running or is jammed.  
         [0060]    Preferred values of the components in FIG. 4  
                                                             Motor:                                        Operating voltage   8 to 16 V           Power consumption   0.5 W           Rotation speed   2800 RPM           Transistors 56, 62   BC817/40           Transistors 136, 150, 170   ½ BC857BS           Other transistors   ½ BC847BS           Diodes 164   BAV99           Diodes 82, 88   BAS216           Capacitors 126, 128   4′/ nF           Capacitor 84   6.8 nF           Capacitor 90   3.3 nF           Capacitor 146   220 nF           Resistors 104, 106, 118, 122, 134, 154, 172   10 kΩ           Resistors 108, 110, 156, 160, 174, 178, 190   100 kΩ           Resistors 112, 114   15 kΩ           Resistor 166   51 kΩ           Resistor 116   39 Ω           Resistors 140, 144   1 MΩ                      
 
         [0061]    Many variants and modifications are of course possible within the scope of the present invention. Therefore, the invention is not limited to the particular embodiments shown and described, but rather is defined by the following claims.