Abstract:
An electronically commutated electric motor ( 110 ) has a permanent-magnet rotor ( 28 ), a stator having a stator winding arrangement ( 40 ), a motor control module ( 20 ) implemented as an IC and having a control logic unit ( 27 ), and an external power stage ( 50 ), separate from the IC, for influencing the current flow in the stator winding arrangement ( 40 ). The motor control module ( 20 ) has an internal power stage ( 29 ) having at least one open collector output ( 21, 23 ). The control logic unit ( 27 ) is configured to process a rotor position signal ( 24′, 24 ″) and to generate therefrom control signals ( 27′ ) for the internal power stage ( 29 ), which control signals ( 27′ ) serve to apply control to the internal power stage ( 29 ). Using an external power stage ( 50 ) reduces vulnerability to motor overheating and provides design flexibility.

Description:
CROSS-REFERENCE 
       [0001]    This application is a section 371 of PCT/EP2007/02434 filed 20 Mar. 2007 and published as WO 2007-140832-A1 on 13 Dec. 2007. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an electronically commutated motor (ECM) which has reduced vulnerability to overheating. 
       BACKGROUND 
       [0003]    Integrated motor control modules exist that have an internal power stage for direct connection of at least one stator strand of an ECM. Because of the heat generated in the internal power stage of this module, such modules have the disadvantage that they have little power reserve at high outside temperatures, i.e. they then enable only a low motor power level, or operation of the motor is then no longer possible at all. This is referred to as “derating,” i.e. the maximum power output or “rating” depends on the ambient temperature of the motor module, and decreases or becomes more or less limited with increasing temperature. 
       SUMMARY OF THE INVENTION 
       [0004]    It is therefore an object of the invention to make available a new ECM that can be operated even at higher ambient temperatures. 
         [0005]    According to the invention, this object is achieved by an ECM in which there is an internal integrated control module having an open collector output, an external power stage for influencing current flow in the motor stator, and an inversion logic unit which reshapes an output signal from the open collector output, for the purpose of generating commutation signals for the external power stage. 
         [0006]    A motor of this kind can be operated even at higher temperatures. The combination of an internal power stage, inversion logic unit, and external power stage enables a plurality of circuit variants with which, for example, the switching speed of the power stage can be influenced and adapted to the corresponding application for which the motor will be used. 
     
    
     
       BRIEF FIGURE DESCRIPTION 
         [0007]    Further details and advantageous refinements of the invention are evident from the exemplifying embodiments, in no way to be understood as a limitation of the invention, that are described below and depicted in the drawings. 
           [0000]    In the drawings: 
           [0008]      FIG. 1  is a circuit diagram of an apparatus for operating an electric motor, according to an embodiment of the invention; 
           [0009]      FIG. 2  is a circuit diagram of the external power stage of  FIG. 1 , according to another embodiment of the invention; 
           [0010]      FIG. 3  schematically depicts a characteristic curve for the apparatus according to  FIG. 1  or  FIG. 2 ; 
           [0011]      FIG. 4  is a circuit diagram of the apparatus of  FIG. 1  having a rotation speed output, according to a refinement of the invention; and 
           [0012]      FIG. 5  is a circuit diagram of the apparatus according to  FIG. 1  having an additional device for stabilizing the supply voltage. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    In the description that follows, identical or identically functioning parts are labeled with the same reference characters in the various Figures, and usually are described only once. 
         [0014]      FIG. 1  is a circuit diagram of an apparatus  100  for operating an ECM  22 , which latter has a permanent-magnet rotor  28  and a stator winding arrangement  40 . The latter is depicted, by way of example, in two-stranded fashion, i.e. having two winding strands  42 ,  44 . These are connected on the one hand via a supply lead  110  to a DC voltage source VCC, and on the other hand to an external power stage  50 . Voltage source VCC is connected via a supply lead  120  to a motor control module  20  (CONTROLLER IC). The ends of strands  42 ,  44  connected to supply lead  110  are referred to hereinafter as “upper” ends, whereas the ends connected to external power stage  50  are referred to as “lower” ends  43 ,  45 . 
         [0015]    External power stage  50  serves to influence the currents in winding strands  42 ,  44 , and has two semiconductor switches that are depicted in  FIG. 1  by way of example as bipolar transistors  52 ,  54 . (A version having field effect transistors is also described later.) The collector of transistor  52  is connected to lower end  43  of strand  42 , its emitter to ground (GND), and its base to an inversion logic unit  30 . Analogously, the collector of transistor  54  is connected to lower end  45  of strand  44 , its emitter to ground (GND), and its base to inversion logic unit  30 . The latter serves to generate suitable commutation signals  51 ′,  53 ′ for external power stage  50 , and has two semiconductor switches, which are depicted in  FIG. 1  by way of example as bipolar transistors  32 ,  34 , as well as eight resistors  31 ,  33 ,  35 ,  37 ,  51 ,  53 ,  71 ,  73 . The collector of transistor  32  is connected via resistor  35  to supply lead  110 , and via resistor  51  to the base of transistor  52 . Its emitter is connected to ground (GND), and its base is connected via resistor  31  on the one hand to an open collector output  21  of motor control module  20  in order to deliver an output signal  21 ′, and on the other hand via resistor  73  to lead  110 . 
         [0016]    Analogously, the collector of transistor  34  is connected via resistor  37  to lead  110 , and via resistor  53  to the base of transistor  54 . Its emitter is connected to ground, and its base is connected via resistor  33  on the one hand to open collector output  23  of motor control module  20  in order to deliver an output signal  23 ′, and on the other hand via resistor  71  to lead  110 . 
         [0017]    The following are integrated into module  20  that is depicted: 
         [0018]    a Hall sensor  24  (HALL); 
         [0019]    a rotor position preparation unit  25  (HALL_PREP); 
         [0020]    an error logic unit  26  (ERROR LOGIC); 
         [0021]    an internal control logic unit  27  (CONTROL LOGIC) that is also responsible for current flow and commutation; and 
         [0022]    an output unit or internal power stage  29  (OC-OUT) having at least one open collector output. 
         [0023]    Module  20  can be implemented as a space-saving motor control IC, which also exists as an Application-Specific Integrated Circuit (ASIC) module. Motor control ICs of this kind are available on the market, e.g. the AH287 of the Anachip company, or the PT3911 of Prolific Technology Inc. Modules  20  usually serve to connect lower ends  43 ,  45  of strands  42 ,  44  directly to open collector outputs  21 ,  23 , and to generate corresponding output signals  21 ′,  23 ′ for current flow and commutation. They are available, for example, with a power rating of up to 2 watts and a voltage range between 2.8 V and 28 V. 
         [0024]    Integrated Hall sensor (rotor position sensor)  24  is arranged in the magnetic field of rotor  28  in order to generate a rotor position signal  24 ′ during operation. Alternatively, any rotor position sensor (including an external one) can also be used. This can be disadvantageous because such a sensor usually requires a capacitor in order to generate a stall clock cycle, with corresponding costs and a corresponding space requirement, as well as a stabilizing circuit for voltage stabilization in order to prevent overload and enable sufficiently precise measurement. It is likewise possible to sense the rotational position of rotor  28  using the so-called sensorless principle, as is known to one skilled in the art. In  FIG. 1 , Hall sensor  24  is depicted as an integrated component of module  20 . 
         [0025]    Rotor position signal preparation unit  25  serves to prepare rotor position signal  24 ′ generated by Hall sensor  24 , and it generates a rotor position signal  24 ″. Control unit  27  generates, from rotor position signal  24 ″, a signal  27 ′ for applying control to power stage  29  with its power components, in order to produce commutation of and current flow in stator winding arrangement  40 . In the arrangement according to  FIG. 1 , power stage  29  has two open collector outputs  21 ,  23 . Other numbers of such outputs are possible. 
         [0026]    Error logic unit  26  serves as stall protection for ECM  22 , and switches it off in the event of an error, for example if rotor  28  is mechanically stalled. Error logic unit  26  generates, for this purpose, an error signal for control unit  27 . The latter, on the basis of the error signal, generates the commutation signals in such a way that external power stage  50  is switched off. It is thus possible, for example if rotor  28  is stalled, to prevent overheating of ECM  22  due to continued current flow through stator winding arrangement  40 , and to enable reliable restarting after the stall. Module  20 , inversion logic unit  30  and external power stage  50  can be arranged together on a common circuit board, if appropriate. 
       Operation 
       [0027]    During operation, motor control module  20  generates signals  21 ′,  23 ′ for ECM  22 . For this purpose, Hall sensor  24  senses the rotational position of rotor  28  and generates a rotor position signal  24 ′ that is prepared in unit  25 . As a function of the prepared rotor position signal  24 ″ and depending on the state of error unit  26 , control signals  27 ′ for internal power stage  29  are generated in control unit  27 . Said power stage is controlled by control signals  27 ′ in such a way that it generates signals for commutation of ECM  22 , which are outputted via outputs  21 ,  23  as signals  21 ′,  23 ′. 
         [0028]    Open collector outputs  21 ,  23  enable a direct connection of lower ends  43 ,  45  of strands  42 ,  44 . A logical LOW signal is therefore outputted at open collector output  21  when winding strand  42  is to receive current, i.e. output  21  is connected to ground GND. Analogously, a logical LOW signal is outputted at output  23  when winding strand  44  is to receive current; preferably, a logical LOW signal is outputted at no more than one of outputs  21 ,  23  at any moment. 
         [0029]    In order to interrupt current flow in one or both winding strands  42 ,  44 , a logical TRISTATE signal is generated at the associated output  21 ,  23 , i.e. outputs  21 ,  23  are switched to high impedance so that no control current can be taken from them. An interruption of the current flow in both winding strands  42 ,  44  is necessary, inter alia, in the so-called current-flow gap and when rotor  28  is stalled (as described) in the event of a fault. 
         [0030]    Because outputs  21 ,  23  are not connected directly to lower ends  43 ,  45  of the windings in the context of the circuits shown in  FIGS. 1 ,  4 , and  5 , but instead are used to apply control to external power stage  50 ,  50 ′, etc., output signals  21 ′,  23 ′ are inverted by inversion logic unit  30 . The result is that output signal  21 ′ generated at output  21  is inverted by transistor  32 , and output signal  23 ′ generated at output  23  is analogously inverted by transistor  34 . A logical HIGH signal is generated at the collector of transistor  32  or  34 , as a commutation signal for external power stage  50 , when a logical LOW signal is present at the transistor&#39;s base, and vice versa. 
         [0031]    Suitable switching thresholds and switch-on and switch-off times for transistors  32 ,  34  can be set by means of resistors  31 ,  33 ,  71 ,  73 . 
         [0032]    The signals generated at the collectors of transistors  32 ,  34  are the commutation signals for external power stage  50 . These signals cause transistor  52  or  54  to become or be switched on when a logical HIGH signal is generated at its base (and thus at the collector of transistor  32  or  34 , respectively). Switching on transistor  52  or  54  causes a current to flow through that transistor and through the associated winding strand  42  or  44 , respectively. Conversely, transistor  52  or  54  becomes or is switched off when a logical LOW signal is generated at its base (and thus at the collector of transistor  32  or  34 , respectively). Because a current through transistor  52  or  54  is thereby suppressed, current also does not flow through the associated strand  42  or  44 , respectively. Current flow in both strands  42 ,  44  is correspondingly interrupted when both transistors  52 ,  54  are switched off. 
         [0033]    Suitable switch-on and switch-off times for external power stage  50  are set by means of a delay member constituted by resistors  35 ,  37 ,  51 ,  53 , which is depicted by way of example as an integrated constituent of inversion logic unit  30 . Be it noted, however, that it can also be implemented as part of external power stage  50  or as a separate component. The delay member can be used to reduce voltages that would otherwise occur upon commutation in winding strands  42 ,  44 . 
         [0034]    With only a small number of components and thus at low cost, inversion logic unit  30  makes possible a connection (not actually intended) from external power stage  50  to internal power stage  29 . Dividing the power dissipation between internal power stage  29  and external power stage  50  allows the motor to be operated even at higher temperatures, and in power output classes that are beyond the specification of the motor control module. 
         [0035]      FIG. 2  is a partial depiction of an expanded variant  100 ′ of apparatus  100  according to  FIG. 1 . This variant likewise has an ECM  22 , a module  20 , and an inversion logic unit  30 . In contrast to  FIG. 1 , apparatus  100 ′ has a voltage limiter  90  and a differently configured external power stage  50 ′. 
         [0036]    Voltage limiter  90  serves to limit voltage spikes that are generated by an induced voltage that is induced in stator winding arrangement  40  upon commutation by external power stage  50 ′. This induced voltage produces a recharge current that is recharged into link circuit  110  and consequently to voltage limiter  90 . 
         [0037]    As  FIG. 2  shows, voltage limiter  90  has a link circuit capacitor  92  and/or a Zener diode  94  or both. These are arranged parallel to one another between lead  110  and ground. Capacitor  92  serves to absorb the recharge current, and thus absorbs excess energy from strands  42 ,  44 , thereby reducing corresponding voltage spikes. Zener diode  94  serves to protect link circuit capacitor  92 , and limits a link circuit voltage present thereat. This protects the entire electronic system. 
         [0038]    In contrast to external power stage  50  according to  FIG. 1 , external power stage  50 ′ is depicted with two field effect transistors (FET)  52 ′,  54 ′ having internal recovery diodes  85 ,  86 , respectively. In order to limit the drain voltage of these FETs  52 ′,  54 ′, external power stage  50 ′ has a voltage limiting member having a plurality of elements that can be used separately from one another or in any desired combinations. The elements described below are accordingly to be regarded only as examples of suitable voltage limiters. 
         [0039]    An effective voltage limiter can be implemented using Zener diodes  87 ,  88 . The anode of Zener diode  87  is connected for this purpose to the source (S), and its cathode to the drain (D), of FET  52 ′. Analogously, the anode of Zener diode  88  is connected to the source (S) of FET  54 ′; its cathode is connected to the latter&#39;s drain. A further voltage limiter is implemented by a diode  89  whose anode is connected to the source terminals of both FETs  52 ′,  54 ′. Its cathode is connected to ground. A further voltage limiter is realized by a circuit for slowing down the switching on and switching off of FETs  52 ′,  54 ′. For this, the gate of transistor  52 ′ is connected via a resistor  81  and a capacitor  83  (which form an RC element) to the drain of transistor  52 ′. The gate of FET  54 ′ is connected via a resistor  82  to the anode of a Zener diode  84  whose cathode is connected to the drain of transistor  54 ′. The RC element and the resistor/Zener diode element are alternative possibilities for slowing down the switching-on and switching-off operations of transistors  52 ′,  54 ′. An RC element or a resistor/Zener diode element can also be provided on both transistors  52 ′,  54 ′ in the context of the circuit according to  FIG. 2 . 
         [0040]    It is evident to one skilled in the art that he need use only those of the components described in  FIG. 2  and the following Figures that are necessary for the particular application. 
         [0041]      FIG. 3  provides a schematic depiction  300  of an example of a characteristic curve  310  that depicts the outside or ambient temperature (Ta) permissible, as a function of a respectively occurring internal power dissipation (Pd) of motor control module  20 , during the operation of apparatus  100  of  FIG. 1  (or  100 ′ of  FIG. 2 ). 
         [0042]    The internal power dissipation and the instantaneous ambient temperature result in heating of module  20 , which can negatively affect the latter&#39;s proper operation. The temperature sensitivity of Hall sensor  24  is particularly critical here, since it can cause undefined switching of internal power stage  27  if the temperature is excessive. Characteristic curve  310  therefore indicates the ambient temperature at which the respectively occurring internal power dissipation Pd reaches its permissible maximum in terms of preventing excessive heating of module  20  and ensuring its proper operation. 
         [0043]    In apparatus  100  of FIGS.  1  and  100 ′ of  FIG. 2 , only a relatively low power dissipation occurs in internal power stage  27 , since the latter is not operating as a true power output stage. External power stage  50  ( FIG. 1 ) or  50 ′ ( FIG. 2 ) is instead used for this purpose. 
         [0044]    When characteristic curve  310  indicates, for example, that a maximum ambient temperature Ta of 100° C. is possible for module  20  when internal power stage  27  is operated as a power output stage and module  20  correspondingly generates an internal power dissipation of approximately 220 mW, a higher ambient temperature is therefore possible when external power stage  50  or  50 ′ is used to reduce the internal power dissipation of module  20 . This temperature can be determined, in consideration of a respectively determined specific internal power dissipation of module  20 , from the dashed extension  320  of curve  310 . 
         [0045]    Because the power dissipation of internal power stage  27  is reduced, Hall sensor  24  can therefore be exposed to a higher ambient temperature without causing undefined switching as a result of excessive temperature sensitivity. Apparatus  100  according to  FIG. 1 , or  100 ′ according to  FIG. 2 , can thus be operated at relatively high ambient temperatures. 
         [0046]      FIG. 4  shows a variant  100 ″ of apparatus  100  according to  FIG. 1 . This variant contains all the elements of apparatus  100  of  FIG. 1 . Apparatus  100 ″ additionally has a rotation speed output  66 , which is implemented here by way of example as an open collector output and is connected to the collector of a transistor  64  whose emitter is connected to ground (GND). The base of said transistor is connected via a resistor  62  to open collector output  23  of module  20  in order to generate, from the latter&#39;s output signal, a rotation speed signal. 
         [0047]      FIG. 5  is a circuit diagram of another variant  100 ′″ that once again contains all the elements of apparatus  100  ( FIG. 1 ). 
         [0048]    In contrast to  FIG. 1 , in this case supply lead  110  is directly connected only to the upper ends of winding strands  42 ,  44 . Resistors  35 ,  37 ,  71 ,  73  are connected to an additional supply lead  110 ′ that has a node  112  which is connected via a resistor  63  to supply lead  120  for IC  20 . Node  112  is also connected to the cathode of a Zener diode  65  whose anode is connected to ground. Resistor  63  and diode  65  constitute a device for stabilizing supply voltage V, for module  20 . Thanks to this circuit, module  20  can also be used for motors that are operated with a higher operating voltage (UB_Motor &gt;&gt;UB_Motor control module). 
         [0049]    If module  20  requires higher currents for its operation, i.e. for example, currents of more than 15 mA, this stabilization device can be implemented using a Zener diode and a series transistor that are suitable for handling such higher currents. Here as well, the stabilization outlay is very small, since the current consumed by the motor control module is very low as compared with the motor current. If, conversely, the internal power stage of the motor control module were used, the entire motor current would also need to be stabilized. 
         [0050]    Numerous variants and modifications are of course possible within the scope of the present invention.