Abstract:
A speed control device, whereby individual motor phases of an electronically commutated multiphase electric motor are supplied via corresponding individual phase shifters from a constant voltage supply unidirectionally and unpulsed during time blocks which are derived from stored time block pulse patterns specific to certain speeds. The speed control device permits setting a variety of speeds with relatively little expense and with low operating losses. The speed control device further provides a simple device for setting intermediate speeds by means of low-frequency switching between at least two time block pulse patterns.

Description:
This is a Continuation of International Application PCT/DE99/01044, with an international filing date of Apr. 6, 1999, the disclosure of which is incorporated into this application by reference. 
    
    
     FIELD OF AND BACKGROUND OF THE INVENTION 
     The invention concerns a speed control device for an electronically commutated multiphase electric motor. These types of speed control devices are used in combination with permanently excited electronically commutated multiphase electric motors in motor vehicles, particularly for fan drives or pump drives with a relatively small starting load moment. 
     U.S. Pat. No. 5,563,481 discloses a speed control device for electronically commutated multiphase electric motors with adjustable speeds, in which the pulse width of the supply voltage is modulated by means of a high frequency, inaudible 20 kHz pulse. U.S. Pat. No. 5,589,745 discloses a second speed control device which provides pulse width modulation of the supply voltage by means of a drive circuit with pulse groups that can be adjusted with respect to amplitude and/or duration. However, these known speed control devices require complex hardware and/or expensive software. 
     British Laid-Open Publication GB-OS 1 563 015 (which corresponds to German Laid Open Publication 26 39 055 B2), U.S. Pat. Nos. 4,283,664, and 3,769,555 disclose speed control devices for electronically commutated electric motors having motor phases that can be powered unidirectionally and unpulsed during definable time blocks by phase shifters from a constant voltage supply, depending on rotor position sensor signals, thereby creating torque. 
     For the device of GB-OS 1 563 015, various speeds can be achieved by the assignment of definite pulse patterns to defined speeds. U.S. Pat. No. 4,283,664 provides for setting various speeds by adjustment of the constant voltage supply source. U.S. Pat. No. 3,769,555 permits the setting of various speeds by means of a pulse generator that adjusts pulse width and pulse frequency. 
     OBJECTS OF THE INVENTION 
     According to one object of the present invention, it is sought to provide a variable-speed drive with speeds that can be set as desired, which device can be made at a significantly lower hardware and software expense, while still completely satisfying the required operating conditions. 
     SUMMARY OF THE INVENTION 
     According to one formulation, the present invention is directed to a speed control device that requires less expensive components by applying a unidirectional, unpulsed supply to each of the motor phases, via only one simple, in particular transistorized, phase shifter. Preferably, the phase shifter is connected directly with its neutral side to one terminal of the constant voltage supply. By alternating switching between two (or more) time block pulse patterns, which are assigned respectively to different motor speeds, intermediate speeds can easily be achieved by switching between different time blocks at a switching frequency, that is below audible frequencies. This switching frequency is determined according to the length of the time block and/or the moment of switching. Moreover, this switching frequency is dependent only on the mechanical time constants of the drive system, with a view to ensuring a non-jerking rotational speed setting. The switching losses can thereby be significantly reduced relative to prior art speed control devices employing high frequency pulse width modulation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention and advantageous refinements thereof are described in more detail below with reference to a schematic exemplary embodiment in the drawings, in which: 
     FIG. 1 shows a block diagram of an electronically commutated electric motor with five motor phases each connected to a constant voltage supply via a phase shifter, in accordance with rotor position sensor signals; 
     FIGS.  2 ( a )-( d ) show an assignment of five rotor position sensor signals, shown in FIG.  2 ( e ), to four different time block pulse patterns in an electric motor with a permanent magnet excited rotor having three pairs of poles; and 
     FIG. 3 shows alternating switching between two different time block pulse patterns to attain a speed corresponding to approximately 70% of the nominal speed of the electric motor. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a block diagram of an electronically commutated electric motor with five motor phases, A, B, C, D, and E, which are distributed over the circumference of the stator. Each of the motor phases A-E is powered via a transistorized phase shifter, T 1 , T 2 , T 3 , T 4 , or T 5 , from a constant voltage supply P; N, for example a vehicle electrical system, which provides an unpulsed, unidirectional supply during a time block T B  of the respective phase shifter. A permanently excited rotor (not shown here), which has six permanent magnet poles, and therefore three pairs of poles, induces voltages in the motor phases A-E. These induced voltages are transmitted as rotor position sensor signals S 1 , S 2 , S 3 , S 4  and S 5  to a sensor signal evaluation device SED. Drive commands for the time blocks T B  of the phase shifters T 1 -T 5  are transmitted from the sensor signal evaluation device SED to a microcontroller MC, which is already present as a component of the speed control device. The microcontroller MC then drives the phase shifters T 1 -T 5 , according to the time block pulse patterns PP 1 , PP 2 , PP 3 , and PP 4  that are stored in it. These time block pulse patterns PP 1 -PP 4  are assigned to definite, respective motor speeds. 
     FIGS.  2 ( a )-( d ) show examples of four of these types of time block pulse patterns PP 1 -PP 4 , each with different time blocks T B  for connecting and disconnecting the individual motor phases A-E to the constant voltage supply P; N, in accordance with the rotor position sensor signals S 1 -S 5 . The time block pulse patterns PP 1 -PP 4  depicted in FIG. 2 correspond to a rotor which is equipped with six permanent magnet poles, such that the north and south poles alternate every 60° around the circumference of the rotor. Accordingly, an electrical period T EL  of the induced rotor position signal voltage corresponds mechanically to 120°. FIG.  2 ( e ) shows the induced rotor position sensor signals S 1 -S 5  over the electrical period T EL . From FIG.  2 ( e ), it can be seen that there are ten time segments, in which different rotor positions are detectable. FIGS.  2 ( a )-( d ) show, as a function of the rotor position sensor signals S 1 -S 5 , the respective time blocks T B  during which the individual motor phases A-E are supplied with current, which is unidirectional and unpulsed. The current is supplied in accordance with the rotor position sensor signals S 1 -S 5  and in correspondence to the various time block pulse patterns PP 1 -PP 4 . 
     During a time block T B , that corresponds to {fraction (4/10)} of the maximum possible current supply of a motor phase during an electrical period T EL , in this particular example, the maximum speed of the electric motor will be attained. In this so-called 100% block operation, each of the motor phases is supplied with current for ⅖ T EL  in one current direction, such that two motor phases are supplied at once at any given time. 
     Proceeding from an assignment of the nominal speed of the electric motor to the time block pulse pattern PP 4 ={fraction (4/10)}, correspondingly lower speeds result for the other time block pulse patterns PP 3 ={fraction (3/10)}, PP 2 ={fraction (2/10)}, and PP 1 ={fraction ( 1 / 10 )} depicted. 
     Preferably, the rotor position sensor signals S 1 -S 5  and the associated time block pulse patterns PP 1 -PP 4  are digitally processed, stored, and further processed into signals for driving the phase shifters T 1 -T 5 . The following table shows the digital assignment of the rotor position sensor signals S 1 -S 5  to the associated time block pulse patterns PP 1 -PP 4 , for the motor phases A-E, in each of the ten time segments. The rotor position sensor signals S 1 -S 5  are induced in the five motor phases A-E during rotation of the permanently excited rotor having three pairs of poles. Each of the associated time block pulse patterns PP 1 -PP 4  corresponds to its respective connection and disconnection time blocks T B . The ten time segments correspond to the maximum possible subdivision of T EL  in the example described above and depicted in FIG.  2 . 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
               
               
                          Time 
                 S1-S5 
                 PP1 1/10 
                 PP2 2/10 
                 PP3 3/10 
                 PP4 4/10 
               
               
                 Slot 
                 54321 
                 EDCBA 
                 EDCBA 
                 EDBCA 
                 EDBCA 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1. 
                 10001 
                 00000 
                 00001 
                 10001 
                 10001 
               
               
                 2. 
                 11001 
                 10000 
                 10000 
                 10000 
                 10001 
               
               
                 3. 
                 11000 
                 00000 
                 10000 
                 11000 
                 11000 
               
               
                 4. 
                 11100 
                 01000 
                 01000 
                 01000 
                 11000 
               
               
                 5. 
                 01100 
                 00000 
                 01000 
                 01100 
                 01100 
               
               
                 6. 
                 01110 
                 00100 
                 00100 
                 00100 
                 01100 
               
               
                 7. 
                 00110 
                 00000 
                 00100 
                 00110 
                 00110 
               
               
                 8. 
                 00111 
                 00010 
                 00010 
                 00010 
                 00110 
               
               
                 9. 
                 00011 
                 00000 
                 00010 
                 00011 
                 00011 
               
               
                 10. 
                 10011 
                 00001 
                 00001 
                 00001 
                 00011 
               
               
                   
               
             
          
         
       
     
     According to the present invention, intermediate speeds can be produced by switching between the individual table entries of the time block pulse patterns by proceeding from the defined assignment of the rotor position sensor signals S 1 -S 5  to the driving signals of the phase shifters T 1 -T 5  of the individual motor phases A-E in the form of time block pulse patterns PP 1 -PP 4 . Preferably, this assignment is stored in the previously mentioned tabular form, in a ROM within the microcontroller MC. In addition to changing the durations of the time blocks T B , speed can also be changed by switching on the time blocks T B  at different moments corresponding to a division of the time segments. Setting the speed by alternating or time-oriented switching of the stored time block pulse patterns is, preferably, also predefined and stored. 
     The switching frequency f S  forms the basis for switching between different time block pulse patterns and is dependent on the mechanical time constants of the motor system. Based upon the situation given, the switching frequency f S  can be advantageously provided within a range of a few Hertz, in particular below the threshold of audibility. 
     FIG. 3 depicts driving of the motor phases A-E for a speed corresponding to approximately 70% of the nominal motor speed. To attain this exemplary speed, a switching frequency f S  is provided for switching in appropriate proportion between a time block pulse pattern that corresponds to a motor speed higher than the desired speed (e.g., PP 4 ), and a time block pulse pattern that corresponds to a motor speed lower than the desired speed (e.g., PP 2 ). The switching frequency f S  is set, e.g., in such a way that for 40% of its period a time block pulse pattern PP 4 ={fraction (4/10)} is used, while, for the remaining 60% of the period of the switching frequency f S , a time block pulse pattern PP 2 ={fraction (2/10)} is used. For the assumed pole pair number p=3, the duration of the electrical period T EL  is one-third of the duration of the mechanical period T MECH . 
     The dwelling time in a specific operating condition of a time block pulse pattern determines the mean speed which the electric motor assumes. In any operating condition, the electric motor develops a specific driving torque, which leads to a specific operating speed corresponding to the effective known load. Therefore, for a defined load moment of any operating condition, a specific speed can be assigned and stored in the microcontroller for a specific request. 
     When the motor is started, an excessive current load can be easily avoided by selecting an appropriate start mode with a corresponding time block pulse pattern by the microcontroller. 
     The above description of the preferred embodiments has been given by way of example. From the disclosure given, those skilled in the art will not only understand the present invention and its attendant advantages, but will also find apparent various changes and modifications to the structures and methods disclosed. It is sought, therefore, to cover all such changes and modifications as fall within the spirit and scope of the invention, as defined by the appended claims, and equivalents thereof.