Abstract:
An electronically commutated motor has a rotor and a stator interacting with one another. A semiconductor control member controls a motor current supplied to the stator. An arrangement is provided that detects values of the motor current which surpass a preset threshold value and generates a first signal upon surpassing the threshold value. An arrangement is provided that determines rotational speed values of the motor, which surpass a preset rotational speed, and generates a second signal upon surpassing the preset rotational speed. An arrangement is provided that combines the first and second signals for generating a combined signal, wherein the combined signal acts substantially without temporal delay on the semiconductor control member and reduces the motor current to a value which is greater than zero.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an electronically commutated motor. Numerous such motors are known. 
     For such motors it is desirable that they run with a low noise level during operation. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a novel electronically commutated motor. 
     According to the invention, this object is solved by a motor comprising an arrangement for detecting values of the motor current, which surpass a preset threshold value, and for generating a first signal upon surpassing this threshold value, further comprising an arrangement for determining rotational speed values, which surpass a preset rotational speed, and for generating a second signal upon surpassing the predetermined rotational speed, and comprising an arrangement for combining the first and second signals for generating a combined signal, which acts substantially without temporal delay on a semiconductor control member controlling the motor current and during its action reduces this motor current to a value which is greater than zero. Such a motor makes possible, on the one hand, a fast acceleration and, on the other hand, a smooth running at its operational rotational speed because, as a result of the current limitation that is active then, current peaks are effectively suppressed and this very efficiently lowers the noise level of such a motor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further details and advantageous developments of the invention result from the embodiment described in the following and illustrated in the drawing, which embodiment is not to be understood in any way as a limitation of the invention. It is shown in: 
     FIG. 1 a circuit diagram of a preferred embodiment of a motor according to the invention; and 
     FIG. 2 a diagram illustrating the motor according to FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows schematically to the right a so-called two-pulse motor  10  with two stator winding phases  12  and  14  and a permanent-magnetic rotor  16  whose magnetic field controls a rotor position sensor  18  in the form of a Hall IC which is also illustrated in FIG. 1 all the way to the left and is connected with a positive line  20  and a negative line  22  between which a suitable direct-current voltage is supplied, for example, 12, 24 or 60 V. Rectangular pulses  26  with a frequency which is proportional to the rotational speed of the rotor  16  are supplied during operation to a terminal  24  of the Hall IC. The terminal  24  it is connected by a so-called pull-up resistor  28  to the pulse line  20 . 
     The pulses  26  are supplied by a resistor  30  directly to the base of a npn transistor  32  which controls the current i 12  in the winding phase  12  whose one terminal is connected with the collector of the transistor  32  and whose other terminal is connected to the positive line  20 . The emitter of the transistor  32  is connected with a line section  34  which is connected by a low-resistance measuring shunt  36  with the negative line  22 . The measuring shunt  36  serves as a sensor member for the motor current I. 
     The other winding phase  14  is controlled by a npn transistor  40 . For this purpose, one terminal is connected with the collector of the transistor  40 , and the other connector is connected with the positive line  20 . The emitter of the transistor  40  is connected with the line section  34 . 
     Between collector and base of the transistor  32 , a Miller capacitor  42  is arranged, and between the collector and the base of the transistor  40  a Miller capacitor  44  is arranged. When, for example, the transistor  32  is switched on, the Miller capacitor  42  slows the current increase, and when this transistor is switched off, the Miller capacitor  42  slows the current drop. The same holds true for the transistor  40 . Accordingly, the motor noise during commutation is correspondingly reduced. 
     A npn phase reversal transistor  46  serves for controlling the transistor  40 , wherein its emitter is connected with the negative line  22 , its base is connected via the resistor  48  with the junction  24 , and its collector is connected via resistor  50  with the positive line  20  and via resistor  52  with the base of the transistor  40 . 
     When thus the potential at the junction  24  is high, the transistor  32  is switched on via the resistor  30  and the winding phase  12  is supplied with current while the winding phase  14  is current-less because the transistor  46  is conducting and thus blocks the transistor  40 . 
     When, on the other hand, the potential at the junction  24  is low, the transistors  32  and  46  are blocked. Via the resistors  50  and  52  the base of the transistor  40  receives a current which switches on this transistor so that now the winding phase  14  is supplied with current. 
     The winding phases  12  and  14  obtain thus alternating current pulses, corresponding to the position of the rotor  16 , as is known to a person skilled in the art. This is known as a two-pulse motor. 
     When a preset rotational speed is reached, the current is to be reduced in the winding phases  12 ,  14  so that the rotor  16  will not rotate too fast. 
     For this purpose, the rectangular pulses  26  are supplied via the capacitor  58 , functioning as a differential member, a junction  59 , and a first diode  60  to an integrator member  62  which comprises a resistor  64  and a capacitor  66 ; compare FIG. 1. A second diode  68  is arranged between the negative line  22  and the junction  59 , and its cathode is connected to the junction  59 . 
     With increasing rotational speed, the capacitor  66  is thus charged increasingly, i.e., the voltage u c  thereat is a measure for the rotational speed of the rotor  16 . 
     The voltage u c  is supplied via a resistor  70  to the base of a npn transistor  72  and via a resistor  72  to the base of a npn transistor  76 . The emitter of both transistors are connected to the junction  78 , to which the collector of a npn transistor  8  is also connected, whose emitter is connected to the negative line  22 . 
     The collector of the transistor  76  is connected with the base of the transistor  32  and the collector of the transistor  72  with the base of the transistor  40 . 
     Accordingly, when the two transistors  76  and  80  are conducting, the base current of the transistor  32  is reduced so that the transistor  32  becomes less conductive. 
     When the transistors  72  and  80  are conductive, the base current of the transistor  40  is reduced so that it becomes less conductive. 
     The base of the transistor  80  is connected to a junction  84  which is preset to a certain potential by means of a voltage divider comprised of three resistors  86  (in the positive line  20 ),  88 , and  90  (in the line section  34 ). For this purpose, a diode  92  is parallel connected to the resistors  88  and  90  in order to maintain the voltage at these two resistors constant. The diode  92 , like the resistor  90 , is also connected the line section  34 . 
     As already described, between the line section  34  and the negative line  22  the measuring shunt  36  is provided through which the motor current I flows. The voltage at the resistor  90  is now selected such that it alone is not sufficient to make the transistor  80  conductive. However, once the current I increases past a predetermined value, a voltage drop occurs at the resistor  36  that, together with the voltage at the resistor  90 , is sufficient in order to make the transistor  80  conductive, as needed for a current limitation. 
     However, as can be easily seen, the transistors  72 ,  76  must additionally also be conductive in order for a current limitation to take place. And these transistors  72 ,  76  become conductive only when the rotational speed and thus the voltage u c  are high enough. 
     The current limitation thus is effective only when the motor has reached its preset rotational speed and thus has reached a preset voltage u c . 
     When, upon reaching the operational rotational speed, the current I surpasses a certain threshold value i t , the current I is limited to this value i t  wherein the threshold value is a selected working point of the motor, which may correspond, for example, to the current I. This suppresses current peaks which would otherwise occur shortly before commutation, and a very constant course of the motor current I results, as illustrated in FIG.  2 . 
     In FIG. 2, the commutation takes place at the rotor positions of 0 electrical degrees, 180 electrical degrees, 360 electrical degrees, and the current here increases only minimally because it is limited very quickly and effectively as a result of the transistor  80  becoming conductive. This results in a very strong reduction of the motor noise, which is advantageous particularly for small fans. 
     In principle, the present circuit thus operates when reaching the operational rotational speeds similar to a constant current member, i.e., the motor current will exhibit more the characteristics of a constant current. 
     Operational Mode 
     When starting the motor  10 , the capacitor  66  is discharged and, therefore, the transistors  72  and  76  are blocked. By means of the rectangular signal  26 , the transistors  32 ,  40  are alternatingly conductively controlled so that from approximately 0 electrical degrees to 180 electrical degrees the current i 12  and from approximately 180 electrical degrees to 360 electrical degrees the current i 14  flows, resulting also in the current peaks  100 ,  102  so that the motor will briefly become somewhat louder during starting. 
     When the operational rotational speed has been reached, the voltage u c  becomes so high that the transistors  72  and  76  become conductive. 
     When the motor current I, for example, in the range of commutation, surpasses the threshold value i t , the transistor  80  is conductive for a short period of time. When, for example, the transistor  32  receives at that moment a control current, so that the current i 12  flows, a part of this control current flows via the transistor  76  and  82  to the negative line  22 , so that the current i 12  is reduced correspondingly. The same holds true for the transistor  40  and the current i 14 . 
     When the rotational speed is too high, the threshold value i t  is lowered, i.e., the current I is limited to a lower value. 
     In this way it is achieved that, during starting of the motor  10 , the current I is not limited which results in a quick acceleration, that, however, upon reaching the desired rotational speed, current peaks will be suppressed in order to reduce the motor noise correspondingly, wherein this suppression simultaneously serves for limiting the rotational speed. 
     It has been found that in this way, especially in the case of motors for small fans, the motor noise can be greatly reduced. Accordingly, this represents a preferred application. Such a motor can, for example, have a power input of 0.5 W. 
     The following preferred parameters result for an embodiment (k=kOhm): 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 operational voltage 
                 13 V (9 . . . 16 V) 
               
               
                   
                 Hall IC18 
                 Allegro UUA 1027BF 
               
               
                   
                 resistors 28, 30, 48, 50, 86 
                 10 k 
               
               
                   
                 resistors 64, 70, 74 
                 200 k 
               
               
                   
                 resistor 88 
                 1 k 
               
               
                   
                 resistor 90 
                 2.2 k 
               
               
                   
                 resistor 36 
                 10 Ohm 
               
               
                   
                 diodes 60, 68 
                 BAS 216 
               
               
                   
                 capacitor 58 
                 10 nF 
               
               
                   
                 capacitor 66 
                 100 nF 
               
               
                   
                 capacitors 42, 44 
                 47 nF 
               
               
                   
                 transistors 72, 76, 80, 92 
                 BC 847 C 
               
               
                   
                 (transistor 92 is connected as a diode) 
               
               
                   
                 transistors 32, 40 
                 BC 817-40 
               
               
                   
                   
               
             
          
         
       
     
     Of course, many variations and modifications are possible within the gist of the present invention.