Abstract:
An electronically commutated electric motor includes a stator and a rotor formed as a permanent magnet. A control unit is connected to the stator and configured to energize the stator to produce a rotating magnetic field. The electric motor further includes at least one Hall sensor configured to detect at least a magnitude of a sensor magnetic field produced by a sensor magnet connected to the rotor. The electric motor also includes at least one magneto resistive sensor configured to detect an alignment of a total magnetic field during a rotor revolution of the rotor and to generate a rotor position signal representing this alignment. The total magnetic field includes the sensor magnetic field and an interference magnetic field superimposed thereon. The control unit is further configured to determine the rotor position of the rotor at least depending on the alignment of the total magnetic field.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2012/056539, filed on Apr. 11, 2012, which claims the benefit of priority to Serial No. DE 10 2011 007 147.4, filed on Apr. 11, 2011 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to an electronically commutated electric motor. The electrically commutated electric motor comprises a rotor, which is embodied in particular as a permanent magnet rotor, and a stator. The electric motor also comprises a control unit that is connected to the stator. The control unit is embodied for the purpose of energizing the stator in order to generate a rotating magnetic field. 
     In the case of electric motors that are known in the prior art, Hall sensors are known for ascertaining a rotor position, wherein the electric motor can be controlled in dependence upon the rotor position in order to rotate the rotor. 
     SUMMARY 
     In accordance with the disclosure, the electric motor comprises at least one Hall sensor that is embodied for the purpose of ascertaining at least one magnitude of the sensor magnetic field that is generated by a sensor magnet that is connected to the rotor in particular in the currentless state of the stator. It is further preferred that the electric motor comprises at least one magnetoresistive sensor that is embodied for the purpose of ascertaining an alignment of a total magnetic field during a rotor revolution of the rotor and for the purpose of generating a rotor position signal that represents said alignment, wherein the total magnetic field comprises the sensor magnetic field and an interference magnetic field that is superimposed on said sensor magnetic field. 
     The control unit is connected at the input side to the rotor position sensors. The control unit is embodied for the purpose of ascertaining the rotor position of the rotor at least in dependence upon the alignment of the total magnetic field, at least of a previously stored magnitude of the sensor magnetic field and a magnitude and an alignment of an interference magnetic field that is generated at least by electrical components of the electric motor. Thus, for the purpose of ascertaining the rotor position, it is advantageously possible to ascertain a precise alignment of the sensor magnetic field by means of a vector calculation. 
     The magnitude of a magnetic field is preferably the magnitude of a magnetic flux density of the magnetic field. 
     The magnetoresistive sensor is for example a CMR sensor (CMR=colossal magnetoresistive), an AMR sensor (AMR=anisotropic magnetoresistive), a GMR sensor (GMR=giant magnetoresistive) or a TMR sensor (TMR=tunneling magnetoresistive). The rotor position signal of the magnetoresistive sensor is also referred to hereinunder as an XMR rotor position signal. 
     For this purpose, the interference magnetic field can be stored for example in the form of an interference magnetic field vector—in particular in the form of a vectorial phasor in a complex form—in a storage device of the control unit. It is further preferred that during a rotor revolution, in particular in a currentless state of the stator, a magnitude or in addition an alignment of the sensor magnetic field can be ascertained by the Hall sensor and can be stored in the form of a sensor magnetic field vector in the storage device. During an operation of the electric motor, in particular during an energized operating mode of the electric motor, it is then possible to ascertain by means of the magnetoresistive sensor the previously mentioned alignment of the total magnetic field. The total magnetic field represents the superposition of the interference magnetic field onto the sensor magnetic field. 
     It is preferred that the control unit is embodied for the purpose of ascertaining by means of vector addition the alignment of the sensor magnetic field in dependence upon the alignment of the total magnetic field and an alignment and a magnitude of the interference magnetic field and a previously stored magnitude of the sensor magnetic field. 
     In a preferred embodiment, the electric motor comprises at least a further Hall sensor. The further Hall sensor is embodied for the purpose of ascertaining the rotor position and for the purpose of generating a further rotor position signal that represents the rotor position, which rotor position signal represents at least a magnitude or in addition an alignment of the sensor magnetic field. 
     It is preferred that the Hall sensor and the further Hall sensor are arranged offset with respect to each other in the direction of the rotor revolution. It is further preferred that the Hall sensor and the further Hall sensor are arranged in an orthogonal manner offset with respect to each other in the direction of the rotor revolution. The offset arrangement and/or the orthogonally offset arrangement of the Hall sensors renders it possible to ascertain the rotor position in an advantageously precise manner, insofar as that in the event of a sinusoidal embodiment the rotor position signals can be evaluated at a point in time when the respective rotor position signal demonstrates a largest temporal change. 
     In an advantageous manner, it is possible by means of the Hall sensor to expand a detection range of the magnetoresistive sensor to a full rotor revolution, in particular 360 degrees, if the detection range of the magnetoresistive sensor amounts to only half a rotor revolution, in particular 180 degrees. 
     In a further advantageous manner, it is possible in addition to ascertaining the angle of the magnetoresistive sensor to also ascertain the magnetic flux density, in particular a magnitude of a magnetic flux density of the sensor magnetic field. 
     The Hall sensor is for example a linear Hall sensor that is embodied for the purpose of generating an analogue output signal. 
     In a preferred embodiment, the Hall sensor and/or the further Hall sensor is a temperature-compensated Hall sensor, wherein the temperature-compensated Hall sensor is embodied for the purpose of generating in particular a digital Hall sensor signal as an output signal independent of a temperature of the temperature-compensated Hall sensor. A digital Hall sensor signal is for example a pulse width modulated signal or an SPI signal (SPI=serial peripheral interface). Thus, the rotor position can be generated in an advantageous manner independently of the temperature, so that the precise rotor position can be advantageously ascertained even in the case of a warm electric motor or when operating the electric motor at minus temperatures of less than zero degrees Celsius. 
     It is preferred that the Hall sensor is a linear Hall sensor that is embodied for the purpose of generating an analogue output signal and that the further Hall sensor is a temperature-compensated Hall sensor that is embodied for the purpose of generating a digital output signal. The output signals of the Hall sensors represent in each case a magnitude in particular a magnitude of a magnetic flux density of the sensor magnetic field that is ascertained by the Hall sensor. 
     It is preferred that the control unit is embodied for the purpose of generating a total Hall sensor signal from the rotor position signals of the Hall sensor and of the further Hall sensor, and the sensor magnetic field is embodied for the purpose of ascertaining in particular the magnitude and the alignment of the sensor magnetic field in dependence upon the total Hall sensor signal. It is preferred that the total Hall sensor signal is a quadrature signal wherein in the case of the quadrature signal the Hall sensor and the further Hall sensor are orthogonally offset with respect to each other in the direction of the rotor revolution. 
     This orthogonal arrangement renders it advantageously possible to ascertain the rotor position in a particularly precise manner by means of the control unit. It is further preferred that the control unit can ascertain the rotor position in dependence upon the XMR rotor position signal or in addition in dependence upon the total Hall sensor signal during an operation of the electric motor. It is thus advantageously possible by means of the total Hall sensor signal to perform an additional process for ascertaining the rotor position, which supplements in a redundant manner the rotor position that is ascertained by means of the magnetoresistive sensor. 
     In a preferred embodiment of the electric motor, the control unit is embodied for the purpose of ascertaining an alignment or in addition the magnitude of the total magnetic field in dependence upon the total Hall sensor signal, in particular the quadrature signal. Thus, the total magnetic field can be advantageously ascertained by means of two mutually different sensor types and the level of accuracy in ascertaining the rotor position can be improved. 
     It is preferred that the temperature-compensated Hall sensor comprises an operating voltage that corresponds to an operating voltage of the control unit. Thus, the electric motor advantageously does not require a voltage convertor for generating a separate operating voltage for the Hall sensor. 
     The disclosure also relates to a method for operating an electronically commutated electric motor, in particular for operating the electric motor of the type described above. 
     In the case of the method for operating an electronically commutated electric motor, at least one magnitude of a sensor magnetic field that is generated by a sensor magnet that is connected to the rotor is ascertained by means of a Hall sensor in particular in the currentless state of the stator and stored. Furthermore, a total magnetic field is ascertained by means of a magnetoresistive sensor during a rotor revolution and a rotor position signal that represents the alignment is generated, wherein the total magnetic field comprises the sensor magnetic field and an interference magnetic field that is superimposed on said sensor magnetic field, wherein by means of a vector calculation an alignment of the sensor magnetic field is ascertained in dependence upon the ascertained alignment of the total magnetic field, the previously stored magnitude of the sensor magnetic field and a magnitude and an alignment of an interference magnetic field that is generated by electrical components of the electric motor. 
     It is preferred that in the case of the method that uses a further Hall sensor, the total magnetic field is ascertained and a further Hall sensor signal is generated. A total Hall sensor signal is formed from the Hall sensor signal and the further Hall sensor signal, which total Hall sensor signal represents the sensor magnetic field. 
     It is preferred that the total Hall sensor signal is a quadrature signal, which represents two Hall sensor signals that are phase-shifted 90° with respect to each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is described hereinunder with reference to the figures and further exemplary embodiments. Further advantageous embodiments are evident in the features of the dependent claims and in the features that are described in the figures. 
         FIG. 1  illustrates an exemplary embodiment for an electronically commutated electric motor, wherein a magnetic interference field can be eliminated during the process of ascertaining a rotor position; 
         FIG. 2  illustrates a locus plot in which the magnetic inference field and the field of a sensor magnet and a principle of the calculated elimination of the interference field for the purpose of ascertaining the magnetic field of the sensor magnet. 
         FIG. 3  illustrates an example for a method for operating an electronically commutated electric motor. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an exemplary embodiment for an electronically commutated electric motor  1 . The electronically commutated electric motor  1  comprises a rotor  5  that is embodied in particular as a permanent magnet rotor. The rotor  5  is mounted in such a manner as to be able to rotate about an axis of rotation  10 . The rotor  5  comprises a sensor magnet  6  that is connected to the rotor  5 , which sensor magnet is arranged in such a manner that it is possible by means of at least one Hall sensor, in this exemplary embodiment the Hall sensors  14  and  16 , to ascertain a sensor magnetic field that is generated by the sensor magnet  6 . The Hall sensor  14  is for example a linear analogue Hall sensor, the Hall sensor  16  is for example a temperature-compensated Hall sensor that is embodied for the purpose of generating in particular a digital output signal that represents the magnetic flux density of a magnetic field that is ascertained by the Hall sensor  16 . 
     The electric motor  1  also comprises a stator  3 . The stator  3  comprises stator coils, in this exemplary embodiment three stator coils  7 ,  8  and  9 . The stator coils  7 ,  8  and  9  comprise in each case a first and a second connector, wherein the second connectors of the stator coils  7 ,  8  and  9  are mutually connected in an electrical manner by means of a common star-point connection  11 . 
     The stator coil  7  is connected by its first connector by means of a connecting line  43  to an output of a power circuit output stage  18  of the electric motor  1 . The stator coil  8  is connected by its first connector by means of a connecting line  44  to the output of the power circuit output stage  18 . The stator coil  9  is connected by its first connector by means of a connecting line  45  to the output of the power circuit output stage  18 . The power circuit output stage  18  comprises for example two transistor half bridges for each stator coil of the stator. It is also feasible to use a B6 transistor bridge as the power circuit output stage. The transistors are for example in each case IGBT transistors (IGBT=insulated gate bipolar transistor) or FET transistors (FET=field effect transistor), in particular MIS-FET transistors (MIS=metal-insulated semiconductor). 
     The electric motor  1  also comprises a processing unit  20  that is connected at the output side by way of a multi-channel connection  30  to the power circuit output stage  18 . The processing unit  20  is embodied for the purpose of controlling the power circuit output stage  18  by way of the connection  30  for the purpose of energizing the stator coils  7 ,  8  and  9  in such a manner that it is possible by means of the stator coils  7 ,  8  and  9  to generate a rotating magnetic field in order to rotate the rotor  5 . 
     The electric motor  1  also comprises a magnetoresistive sensor  12  that—indicated by the broken line—is rotatably connected to the rotor  5 . The magnetoresistive sensor  12  is embodied for the purpose of ascertaining a rotor position of the rotor  5 , in particular a rotor angular position of the rotor  5  and for the purpose of generating an XMR rotor position signal that represents the rotor position of the rotor and for the purpose of outputting said position signal at the output side by way of a connecting line to the processing unit  20 . For this purpose, the magnetoresistive sensor  12  is connected by way of the connecting line  42  to the processing unit  20 . 
     The Hall sensor  14  is connected at the output side by way of a connecting line  38  to the processing unit  20 . The Hall sensor  16  is connected at the output side by way of a connecting line  40  to the processing unit  20 . 
     The operating mode of the electric motor  1  is explained hereinunder: 
     During the operation of the electric motor  1 , magnetic interference fields are generated by electrical components for example by the connecting lines  32 ,  34  and  36  of the electric motor, which magnetic interference fields are superimposed on the magnetic field of the sensor magnet  6 . The Hall sensors  14  and  16  are embodied in each case for the purpose of ascertaining the magnetic field of the sensor magnet  6  and for the purpose of generating a corresponding rotor position signal. The processing unit  20  is embodied for the purpose of evaluating the rotor position signals of the Hall sensors  14  and  16  at a point in time when the stator coils  7 ,  8  and  9  are not in an energized state and for the purpose of ascertaining and storing a magnitude of the sensor magnetic field, in particular a magnitude of the magnetic flux density of the sensor magnetic field. The flux density of the sensor magnetic field can be ascertained by means of the processing unit  20  by means of mathematical rules for complex phasors. 
     For this purpose, the processing unit  20  can comprise the storage device  22  or can be connected to said storage device. 
     In this exemplary embodiment, the storage device  22  stores a magnitude and an alignment of an interference magnetic field  24 . The interference magnetic field  24  is ascertained for example in dependence upon a mathematical model. 
     In this exemplary embodiment, the storage device  22  also stores a data set  26 . The data set  26  represents a magnitude of the magnetic field of the sensor magnet  6 , which magnetic field is ascertained by the Hall sensors and  16 . The processing unit  22  can ascertain the magnitude of the sensor magnetic field for example in dependence upon a quadrature signal that is formed from the rotor position signals of the Hall sensors  14  and  16 . 
     The processing unit  20  is embodied for the purpose of ascertaining during an operation of the electric motor  1  the rotor position of the rotor  5  in dependence upon a total field that is ascertained by the magnetoresistive sensor  12 , in particular an alignment of the total field, wherein in order to ascertain the rotor position the processing unit  20  is embodied for the purpose of ascertaining the alignment of the sensor magnetic field of the sensor magnet  6  by means of vector summation from the interference field vector that is represented by the data set  24 , and the previously stored magnitude of the sensor magnetic field. 
     It is advantageous if at least one of the Hall sensors  14  and  16  is a temperature-compensated Hall sensor. 
     The previously mentioned vectors, in particular the interference field and the magnetic field of the sensor magnet  6  are illustrated hereinunder in  FIG. 2  in a locus plot in a complex plane. 
       FIG. 2  illustrates a locus plot  50  wherein a real part of the magnetic field vectors mentioned in relation to  FIG. 1  is plotted on an X-axis  52  and an imaginary part of the magnetic field vectors that are mentioned in the description relating to  FIG. 1  is plotted on a Y-axis  54 . An angle of the vectors in the complex plane corresponds to a rotor angle of a rotor, a full revolution of the vectors in the complex plane corresponds to a full rotor revolution of the rotor. 
     The vector  56  represents the magnetic field of the sensor magnet that is illustrated in  FIG. 1 , in particular a magnetic flux density of the magnetic field of the sensor magnet. The vector  58  represents the magnetic field of the interference field mentioned in  FIG. 1 . The vector  56 ′ represents the vector  56  that is added in a parallel-offset manner to the end of the vector  58 . The direction  60  of the total field that can be ascertained by the magnetoresistive sensor  12  illustrated in  FIG. 1  originates from an origin of the coordinate system. If the magnitude of the vector is known then it is possible by means of vector addition of the vector  58  and the parallel-shifted vector  56 ′ to ascertain the alignment of the vector  56  in dependence upon the alignment  60  of the total magnetic field and the magnitude of the vector  56  if an alignment and a magnitude of the interference vector  58  that represents the interference magnetic field is known. 
     A vector  59  is also illustrated that represents a magnitude of a magnetic field of the sensor magnet  6  shown in  FIG. 1 , which magnitude has not been ascertained precisely. 
     If the magnitude of the vector of the sensor magnetic field is not ascertained precisely by means of the Hall sensors, then the result is an incorrect alignment of the sensor magnetic field on the previously described vector calculation, in particular according to mathematical rules for complex phasors, which incorrect alignment is represented by an alignment of the vector  59 . 
     A quadrature signal is advantageously formed by the processing unit  20  shown in  FIG. 1  for the purpose of precisely ascertaining the vector  56  of the sensor magnetic field from the rotor position signals of the Hall sensors  14  and  16 . In a further advantageous manner, at least one of the Hall sensors  14  and  16  can be a temperature-compensated Hall sensor for the purpose of precisely ascertaining the vector  56 . 
       FIG. 3  illustrates a method  70  for operating an electronically commutated electric motor. In a step  72 , an interference field that is caused at least by electrical components of the electric motor is ascertained and an interference field vector is generated, which interference field vector represents the interference field. In a step  73 , a sensor magnetic field of a sensor magnet that is connected to a rotor of the electric motor is ascertained and a vector is generated and stored, which vector represents the sensor magnetic field, at least said vector represents the magnitude of the sensor magnetic field. In a step  74 , a total magnetic field is ascertained, which total magnetic field represents the superposition of the interference magnetic field onto the sensor magnetic field. 
     In a step  75 , the direction of the sensor magnetic field is ascertained in dependence upon the total magnetic field that is ascertained in the step  74 , in particular the direction of the total magnetic field and the vectors that are ascertained and stored in the steps  72  and  43 . 
     In a step  76 , the electric motor for generating a magnetic rotational field is controlled in dependence upon the rotor position that corresponds to the direction of the sensor magnetic field that is ascertained in the step  75 .