Abstract:
An electronically commutated direct-current motor has a permanent-magnet rotor ( 19 ), a stator ( 2 ) that has at least one drive winding ( 25 ), and an H-bridge circuit ( 52 ) in which two bridge elements are configured as transistors ( 54, 56 ) and the other two bridge elements as resistors ( 58, 60 ), the drive winding ( 25 ) being arranged on the diagonal of said H-bridge circuit ( 52 ); and it has a commutation circuit for alternate activation and deactivation of the two transistors ( 54, 56 ) of the H-bridge circuit ( 52 ). The motor operates quietly and with unusual reliability, and is well adapted for driving a fan.

Description:
Cross-reference to related patent documents: German Utility Model DE-U1-295 01 695.7 and German Utility Model DE 8 702 271. 
     FIELD OF THE INVENTION 
     The invention relates generally to an electronically commutated direct-current motor (ECM) and, more particularly, to a motor which draws a relatively constant current. 
     BACKGROUND 
     Motors of this kind are used, for example, to drive fans (cf. German Utility Model DE-U1-295 01 695.7 filed Feb. 3, 1995 and published Jul. 20, 1995, assigned to Papst Motoren). In motors of this kind, the actual motor is often physically separated from its electronic components. A motor of this kind is nevertheless intended to start up reliably and above all to run quietly, i.e. with little noise. 
     SUMMARY OF THE INVENTION 
     One object of the invention is to make available a novel electronically commutated direct-current motor. 
     What is obtained by way of the invention is an ECM that is particularly suitable for driving fans, and that has particularly advantageous properties in combination with radial fans. 
     Further details and advantageous developments of the invention are evident from the exemplary embodiment—to be understood in no way as a limitation of the invention—described below and depicted in the drawings. 
    
    
     BRIEF FIGURE DESCRIPTION 
     FIG. 1 is a bottom view of a radial fan that is driven by an electronically commutated motor; 
     FIG. 2 is a section along line II—II of FIG. 1; 
     FIG. 3 shows a circuit according to the present invention that is suitable for operating the fan shown in FIGS. 1 and 2; 
     FIG. 4 shows the voltages that occur during operation between point  3 A and negative line  64 , and between point  3 B and negative line  64 , in FIG. 3; 
     FIG. 5 is a graph of a voltage that occurs during operation at drive coil  25  of FIG. 3, i.e. between  3 A &amp;  3 B; 
     FIG. 6 shows the total current I; 
     FIG. 7 shows the voltage at an output S of the circuit of FIG. 3 when the motor is rotating; and 
     FIG. 8 shows the voltage at output S of FIG. 3 when rotor  19  is jammed or blocked from rotating. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1 &amp; 2 show, as a preferred embodiment, a radial fan  1  whose general structure is known from DE-U1-295 01 695.7. In FIG. 1, this fan  1  is depicted as seen from below, showing a support  2  that is configured as a plastic shaped part. Electrical terminals  3 A,  3 B,  3 C,  3 D, configured for example as terminal pins, and guide pins  4 ,  5  are arranged in shaped part  2  and secured there preferably by injection-molding. These molded-in or inserted terminal pins  3 A,  3 B,  3 C,  3 D are made of electrically conductive material. The one end  7  of pins  3 A,  3 B,  3 C,  3 D is respectively connected conductively to one end of winding terminals  8 , and the other ends  10  of pins  3 A,  3 B,  3 C,  3 D project out of support  2  in the manner depicted. These ends  10  are inserted into openings or depressions, provided for the purpose, of a circuit board  11  (shown in FIG. 2 with dot-dash lines), and soldered there, i.e. connected in contacting fashion to electronic drive system E for motor  12  of fan  1 . A preferred embodiment for such an electronic system E is described in detail with reference to FIGS. 3 and 4. Electronic system E is indicated symbolically in FIG.  2 . It can be located anywhere on circuit board  11 . 
     In its preferred form, motor  12  has a drive winding  25  and a sensor winding  26 , whose terminals  8  are connected via terminal pins  3 A,  3 B,  3 C,  3 D to corresponding terminals on circuit board  11  and from there are supplied with power in accordance with the desired rotation speed and rotation direction. The terminals of drive winding  25  are labeled  3 A and  3 B, the terminals of sensor winding  26   3 C and  3 D. 
     Terminal pins  3 A,  3 B,  3 C,  3 D are of right-angled configuration, the one end  7  being arranged in the plane of the substantially flat support  2 , and end  10  projecting downward out of support  2 . Guide pins  4 ,  5  are also configured as right-angled pins made of an electrically conductive material; their one ends  14  and  15  lie in the plane of carrier  2 , and their other ends  16  and  17  project out of support  2  substantially to the same length as and parallel to the other ends  10  of terminal pins  3 A,  3 B,  3 C,  3 D. 
     A magnetic return path element  18  for a rotor magnet  19 , here a ferromagnetic sheet-metal disk in the form of a circular ring, is injection-molded into shaped part  2 . Attachment means  20 , for example formed as slit snap bolts, are injection-molded onto the underside of shaped part  2 . The attachment means serve as assembly aids and for attaching fan  1  to circuit board  11 . Spacer studs  22  are injection-molded onto the underside of shaped part  2 . These serve to maintain a spacing between the underside of shaped part  2  and circuit board  11 , and can also be used as gauge studs or guide studs. 
     The configuration described above of the stator, in particular of stator support  2 , allows largely automated production; i.e. the winding and placement of winding ends  8  onto pins  3 A,  3 B,  3 C,  3 D, along with soldering and testing, can be accomplished on an automatic apparatus. 
     FIG. 2 shows details of FIG. 1 in section along line II—II of FIG.  1 . The stator winding, which has drive winding  25  and sensor winding  26 , is mounted on a coil body  24  (part of support  2 ). 
     A fan wheel  27  contains a shaft  28  that serves as the rotor shaft. It is mounted radially in a bearing arrangement  29  (sintered double bearing) which is mounted in a bearing support tube  30  that is part of the injection-molded shaped part  2 . An upper rim  32  of bearing support tube  30  that is elongated in the axial direction and has a reduced outside diameter provides axial retention of the bearing in combination with a region of sintered bearing  29  having a reduced outside diameter. Sintered bearing  29  can also, alternatively, be attached by adhesive bonding, caulking, or the like. Mounted in the region of upper rim  32  is a magnetic auxiliary arrangement  34  (ferromagnetic or permanent-magnet arrangement) whose principal function is to bring rotor  19  into a desired staring position upon startup. To reduce costs, this auxiliary arrangement  34  can be formed as a disk that is punched out of magnetic rubber material. 
     A bearing shell  35  placed into bearing support tube  30  forms an axial bearing support for the lower end of shaft  28 . The arrangement of bearing shell  35  determines the size of the substantially flat air gap  36  between rotor magnet  19  and stator winding  25 ,  26 . Reference is made to German Utility Model DE 8 702 271 regarding the construction of the stator winding; for example, windings  25 ,  26  can be wound from two parallel wires, i.e. as a so-called bifilar winding. 
     Fan wheel  27  contains blades  38 , extending substantially radially, which are arranged between a first guidance member  39  and a second guidance member  40 . First guidance member  39  has a central air inlet opening  41  and is of substantially flat configuration. In this exemplary embodiment, the first and second air guidance members  39  and  40  form, viewed in axial cross section, an air outlet cross section that expands outward. 
     Located in the region of air inlet opening  41  is a segment  42  of the fan wheel in which shaft  28  is attached. A ferromagnetic return path disk  44 , on which rotor magnet  19  for motorized drive of fan wheel  27  is arranged, is mounted in second air guidance member  40 . Alternatively, an oriented-pole magnet without a return path disk can be used. As already described, electronic components E (transistors, resistors, etc.) for motor  12  are located on circuit board  11 , and are connected via pins  3 A,  3 B,  3 C,  3 D to windings  25 ,  26  of motor  12 . Components E are thus installed when circuit board  11  is populated. Fan  1  is also installed as a component on circuit board  11 . 
     Components E are often installed by the customer on his or her circuit board  11 , and the customer purchases a “naked” fan  1  and installs it on circuit board  11 , so that an operable electronically commutated motor is created only by that 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. 
     In FIG. 3, drive coil  25  is arranged in an H-bridge  52 . Rotor  19  is symbolically indicated. As it rotates, it induces a voltage in sensor winding  26 , and this is symbolically indicated by a dot-dash line  45 . When motor  12  is running, its commutation is controlled by the voltage induced in sensor winding  26 . Bridge  52  has two npn transistors  54 ,  56  at the bottom, and two resistors  58 ,  60  at the top that are connected to a node  62 . 
     The emitters of transistors  54  and  56  are connected to a negative line  64 . A positive line is labeled  66 . The collector of transistor  54  is connected to terminal  3 A of coil  25 , and the collector of transistor  56  to terminal  3 B. 
     The collector of a pnp Darlington transistor  68 , whose emitter is connected via a resistor  70  to positive line  66 , is connected to node  62 . The base of transistor  68  is connected to the collector of a pnp transistor  72  whose emitter is connected to positive line  66  and whose base is connected to the emitter of transistor  68 . The collector of transistor  72  is connected via a capacitor  74  to node  62 , and via a resistor  76  to negative line  64 . 
     The two transistors  68 ,  72  with their resistors  70 ,  76  constitute a constant-current member  77  that delivers to H-bridge  52  a constant current which contributes to smooth operation of motor  12  and, in combination with a radial fan, results in particularly advantageous properties for such a fan, as will be explained below. 
     A Miller capacitor  78  is located between the collector and base of bridge transistor  54 , and a Miller capacitor  80  analogously in the case of transistor  56 . The purpose of these capacitors is to delay the activation and deactivation of transistors  54 ,  56 , in order to reduce the noise of motor  12  to the greatest extent possible. 
     Sensor winding  26  is arranged between the bases of two substantially identical npn transistors  84  and  86 , whose emitters are respectively connected to negative line  64  and whose collectors are connected, via resistors  88  and  90  respectively, to positive line  66 . Its terminal  3 C is connected to the base of transistor  84 , and its terminal  3 D to the base of transistor  86 . 
     Transistor  84  is connected as a diode, i.e. its collector and its base are interconnected. Transistors  84  and  86  constitute a so-called “current mirror” circuit, i.e. a current that flows through transistor  84  results in a corresponding current in transistor  86 , provided no voltage is induced in sensor coil  26 . Resistor  90  is designed in such a way that the voltage at the collector of transistor  86 , when the motor is switched on, is approximately 50% of the operating voltage between positive line  66  and negative line  64 , so that transistor  54  of H-bridge  52  receives a base current via resistor  90  and its base resistor  92 , and becomes conductive immediately after the motor is switched on. This ensures startup in the correct rotation direction from the starting position. 
     Activation of the other bridge transistor  56  is provided by an npn transistor  96  whose base is connected via a resistor  98  to the collector of transistor  86 , and whose collector is connected to a sensor output S, at which there occurs during operation a rotation-speed-dependent signal S that is depicted in FIG. 7 (signal when motor is rotating) and FIG. 8 (signal when motor is jammed). By way of signal S, it is possible to monitor whether motor  12  is rotating or is jammed. 
     The collector of transistor  96  is connected via a resistor  100  to positive line  66  and via a resistor  102  to the base of transistor  56  Directly after switching on, transistor  96  receives a base current via resistors  90  and  98  and thereby becomes conductive, so that bridge transistor  56  is inhibited. 
     Transistors of the same type, having operating values with only slight deviations from one another, should preferably be used in the current mirror circuit (transistors  84  and  86 ). This yields very reliable operation when the motor is switched on, i.e. reliable activation of bridge transistor  54  and inhibition of transistor  56 . 
     When motor  12  is rotating and transistor  86  is caused, by the sensor voltage at sensor coil  26 , to become fully conductive, transistors  54  and  96  receive no base current and are inhibited, so that transistor  56  becomes conductive. 
     When the rotor is rotating, transistor  86  is controlled by the sensor voltage induced by rotor magnet  19  (FIG. 1) as it rotates in sensor coil  26 , so that as soon as rotor  19  rotates, transistors  54  and  56  are alternatingly activated and deactivated by the voltage at sensor coil  26 . 
     When transistor  54 ; is conductive, a current flows through resistor  70 , transistor  68 , resistor  60 , drive coil  25  (from  3 B to  3 A), and transistor  54  to negative line  64 . When transistor  56  is conductive, a current flows through resistor  70 , transistor  68 , resistor  58 , drive coil  25  (from  3 A to  3 B transistor  56  to negative line  64 . 
     As a result, a current flows in alternating directions through drive coil  25 . Since motors of this kind usually have a low power output, for example 0.4 to 0.7 W, the current that flows in this context through the other of the two resistors  58 ,  60  can be accepted; in other words, it reduces the efficiency, but can be tolerated because of the low power level of motor  12 . 
     A pnp transistor  106  is connected parallel to resistor  60  and a constant-current element  77 . Its collector is connected to terminal  3 B of drive coil  25 , and its emitter to positive line  66 . When this transistor is conductive, a current thus flows directly from positive line  66  via transistor  106 , drive coil  25 , and transistor  54  (now conductive) to negative line  64 , so as to create, when motor  12  is switched on, a high starting current pulse that imparts a vigorous rotation to rotor  19 . 
     Transistor  106  is activated by way of an RC timing member having a capacitor  108  and a resistor  110 . Capacitor  108  is connected to positive line  66  and connected via a node  112  to resistor  110 , which in turn is connected to negative line  64 . Connected to node  112  via a resistor  114  is the base of an npn transistor  116  whose emitter is connected to negative line  64 , and whose collector is connected via a resistor  118  to the base of transistor  106 . 
     Also connected to node  112  via a resistor  120  is the base of an npn transistor  122  whose emitter is connected to negative line  64 , and whose collector is connected directly to the base of transistor  56 . 
     When the motor is switched on, capacitor  108  is discharged, so that node  112  has approximately the potential of positive line  66 . Transistors  116  and  122  thereby become conductive. Transistor  122  inhibits transistor  56 . The effect of transistor  116  is that a base current flows to transistor  106  and makes that transistor conductive, so that as a result, as already described, a high current flows through drive coil  25  (from  3 B to  3 A) when motor  12  is switched on. 
     Capacitor  108  is quickly (e.g. within 0.1 second) charged via resistor  110 , and transistors  106 ,  116 , and  122  are thereafter inhibited as long as motor  12  is switched on. 
     Subsequent to the inhibition of these transistors and under the control of sensor coil  26 , the two output-stage transistors  54  and  56  are alternatingly activated, as already described. This results in the voltage profile shown in FIG. 4, in which u 54  denotes the voltage between the collector of transistor  54  and negative line  64 , and u 56  the voltage between the collector of transistor  56  and negative line  64 . 
     The slope of edge  130  of u 54  is determined by capacitor  78  and resistor  92 . The slope of edge  132  of voltage u 56  is determined by capacitor  80  and resistor  102  The edge slope should not be too steep, in order to keep the noise of motor  12  as low as possible. 
     FIG. 5 shows the voltage u 1  at drive coil  25 . This voltage has a symmetrical profile, which contributes substantially to quiet motor operation. 
     FIG. 6 shows the total current I (cf. FIG. 3) through motor  12 . This current is, for example, 40 mA (within an operating voltage range of 9 to 16 V), and it is evident that this current is very constant; this is achieved using constant-current element  77 . Another way to state this is that after it starts up, ECM  12  continuously operates with current limiting, i.e. the ECM would actually like to receive a higher current, but the latter is held by the constant-current element to a largely constant value, e.g. to 40 mA. 
     This is particularly advantageous in conjunction with a radial fan, since the result is a fan with outstanding characteristics. For example, if an air filter in the air path of this fan is partially clogged, a radial fan of this kind whose ECM  12  is operated with constant current automatically increases its rotation speed, so that air is delivered through such a filter, even when such would no longer be the case with an equivalent axial fan. 
     In addition, if the filter is not clogged, a largely constant rotation speed is obtained over the entire voltage range between 9 and 16 V, for example a rotation speed of approximately 2700 rpm; and that rotation speed is practically unaffected by fluctuations in the operating voltage. 
     FIG. 7 shows voltage S during operation of motor  12 . This is a square-wave voltage whose frequency is twice the rotation speed, e.g. a frequency of 120 Hz at 60 rpm. 
     FIG. 8 shows voltage S in the event of a jammed rotor  19 . In this case, S has either a frequency of zero or, as depicted, a high frequency due to internal oscillations, so that an alarm signal can be generated by way of a connected alarm circuit (not depicted). 
     By changing resistor  70  it is possible to adjust the constant current through constant-current element  77 , and thus the rotation speed of motor  12 . 
     Typical component values are indicated below for a motor  12  with an operating voltage between 9 and 16 V and an operating current of approximately 40 mA at 2700 rpm: 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Resistors 90, 98, 100, 118 
                 10 
                 kΩ 
               
               
                   
                 Resistors 92, 102 
                 0.43 
                 kΩ 
               
               
                   
                 Resistors 58, 60 
                 0.36 
                 kΩ, 250 mW 
               
               
                   
                 Resistor 88 
                 33 
                 kΩ 
               
               
                   
                 Resistor 70 
                 16 
                 Ω 
               
               
                   
                 Resistor 76 
                 4.7 
                 kΩ 
               
               
                   
                 Resistors 110, 114, 120 
                 1 
                 MΩ 
               
               
                   
                 Capacitors 78, 80 
                 330 
                 nF 
               
               
                   
                 Capacitor 108 
                 100 
                 nF 
               
               
                   
                 Capacitor 74 
                 10 
                 nF 
               
               
                   
                 Transistors 54, 56, 84, 86, 96, 116, 122 
                   
                 BC847C 
               
               
                   
                 Transistors 72, 106 
                   
                 BC857B 
               
               
                   
                 Transistor 68 
                   
                 BST60 
               
               
                   
                   
               
             
          
         
       
     
     Many variants and modifications are of course possible in the context 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.