Abstract:
A control device for a permanent magnet motor serving as both a starter for an engine and a generator in a motor vehicle is disclosed. The control device includes a drive circuit converting a direct current to an alternating current to supply the alternating current to the permanent magnet motor, the drive circuit having at least one arm including two series connected first switching elements having flywheel diodes respectively, the drive circuit having an input terminal connected to a capacitor and an output terminal connected to the permanent magnet motor, a chopper circuit including a plurality of series connected second switching elements having diodes connected in parallel with the second switching elements respectively, the chopper circuit being disposed at the battery side and connected in parallel with the capacitor, a reactor connected between a neutral point of the chopper circuit and the battery, and a control for controlling the switching elements of the drive circuit and chopper circuit so that the switching elements are turned on and off.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a control device for controlling a permanent magnet motor serving as both an engine starter and a generator in motor vehicles.  
           [0003]    2. Description of the Related Art  
           [0004]    A starter (self-starting motor) is usually coupled via a clutch with an output shaft of an engine in motor vehicles such as automobiles. The starter is electrically connected via a relay switch to a battery. A dynamoelectric generator is connected via pulleys and belts to the output shaft of the engine. The generator is further connected to the battery. When an ignition key is turned so as to assume a starter position so that a starter relay is operated, a relay switch is turned on so that power is supplied from the battery to the starter. As a result, the starter is rotated so that the output shaft of the engine is rotated, whereupon the engine starts. Thereafter, a clutch is released and the starter relay is returned so that the relay switch is turned off. Upon starting of the engine, the generator is driven for power generation, so that the battery is recharged.  
           [0005]    In the above-described construction, both engine starter and generator for re-charging the battery are required. The requirement results in an increase in a mounting space of the automobile. Furthermore, a large current flows into the starter in starting the engine in order that a large torque may be developed. Accordingly, the starter relay is required to be large sufficiently to withstand the large current flowing into the starter. Additionally, the clutch is provided to prevent the starter from reverse drive by the engine. The clutch further increases the mounting space of the automobile.  
         SUMMARY OF THE INVENTION  
         [0006]    Therefore, an object of the present invention is to provide a control device for controlling a permanent magnet motor serving as both an engine starter and a generator in a motor vehicle, which control device can reduce the mounting space of the motor vehicle and can eliminate a large starter relay.  
           [0007]    The present invention provides a control device for controlling a permanent magnet motor serving as both a starter for an engine and a generator in a motor vehicle, the engine including an output shaft to which the permanent magnet motor is connected, the motor vehicle including a battery. The control device comprises a drive circuit converting a direct current to an alternating current to supply the alternating current to the permanent magnet motor, the drive circuit having at least one arm including two series connected first switching elements having flywheel diodes respectively, the drive circuit having an input terminal connected to a capacitor and an output terminal connected to the permanent magnet motor, a chopper circuit including a plurality of series connected second switching elements having diodes connected in parallel with the second switching elements respectively, the chopper circuit being disposed at the battery side and connected in parallel with the capacitor, a reactor connected between a neutral point of the chopper circuit and the battery, and control means for controlling the switching elements of the drive circuit and chopper circuit so that the switching elements are turned on and off.  
           [0008]    In the above-described arrangement, the permanent magnet motor is connected to the output shaft of the engine so as to serve as the starter for the engine. The permanent magnet motor further serves as the generator recharging the battery after starting of the engine. Thus, the single permanent magnet motor is used as the starter and the generator. Consequently, the mounting space of the motor vehicle can be reduced as compared with the conventional construction in which both starter and generator are individually provided. Furthermore, since no clutch is required between the engine output shaft and the permanent magnet motor, the mounting space can further be reduced. Additionally, the permanent magnet motor is driven by the drive circuit controlled by the control means when operated as the starter. Accordingly, no relay switch as a starter relay is required between the battery and the permanent magnet motor. Consequently, a large starter relay is not required.  
           [0009]    In a preferred form, when the permanent magnet motor is operated as the starter, the control means renders the chopper circuit non-operative or causes the chopper circuit to operate as a step-up chopper so that the control means controls the drive circuit to drive the permanent magnet motor. When the permanent magnet motor is operated as the generator, the control means renders the drive circuit non-operative and causes the chopper circuit to operate as a step-down chopper so that the battery is recharged, in case voltage generated by the permanent magnet motor is higher than voltage of the battery. In case the voltage generated by the permanent magnet motor is lower than the voltage of the battery, the control means renders the chopper circuit non-operative and turns on and off the negative switching element of the drive circuit so that the drive circuit is caused to operate as a step-up chopper so that the battery is recharged.  
           [0010]    In another preferred form, the control device further comprises another chopper circuit connected in parallel with the chopper circuit and including two series connected switching elements having diodes connected in parallel to the switching elements respectively, and another reactor connected between a neutral point of said another chopper circuit and the battery. In further another preferred form, the control means turns on and off the negative switching elements of the two chopper circuits with a timing phase difference by 180 electrical degrees in a case of voltage step-up and turns on and off the positive switching elements of the two chopper circuits with a timing phase difference by 180 electrical degrees in a case of voltage step-down. Additionally, each of the reactors preferably includes a single core and two coils wound on the core. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    Other objects, features and advantages of the present invention will become clear upon reviewing of the following description of preferred embodiments, made with reference to the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 is a circuit diagram showing an electrical arrangement of a control device of a first embodiment in accordance with the present invention;  
         [0013]    [0013]FIG. 2 schematically illustrates an automobile to which the control device is applied;  
         [0014]    [0014]FIG. 3 is a circuit diagram showing part of the electrical arrangement of the control device of a second embodiment in accordance with the invention;  
         [0015]    [0015]FIGS. 4A and 4B are on-off waveform charts of transistors;  
         [0016]    [0016]FIGS. 5A and 5B are on-off waveform charts of the transistors in a phase different from in FIGS. 4A and 4 b;  and  
         [0017]    [0017]FIG. 6 is a view similar to FIG. 3, showing a third embodiment in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]    An embodiment of the present invention will be described with reference to FIGS. 1 and 2. The invention is applied to an automobile in the embodiment. Referring to FIG. 2, an automobile  1  serving as a motor vehicle is schematically shown. An engine  2  is mounted on the automobile  1 . Driving force developed by the engine  2  is transmitted through a transmission  3  and a differential gear  4  to axles  6  of rear wheels  5  respectively. Thus the axles  6  of the rear wheels  5  are drive axles, whereas axles  8  of front wheels  7  are driven axles. A permanent magnet motor such as a brushless motor  9  is mounted on the automobile  1 . The brushless motor  9  includes a stator having a plurality of, for example, three-phase, stator coils  9 U,  9 V and  9 W and a rotor of the permanent magnet type. The brushless motor  9  further includes a rotor shaft (not shown) connected or more specifically, directly connected to an output shaft of the engine  2 . A rechargeable 36-volt battery  10  specified for a hybrid car is also mounted on the automobile  1 . The battery  10  comprises a lead storage battery. Electric power from the battery  10  is supplied via a control device  11  to the brushless motor  9  as will be described later.  
         [0019]    An electrical arrangement of the control device  11  will now be described with reference to FIG. 1. The control device  11  includes an inverter circuit  12  serving as a drive circuit. The inverter circuit  12  includes six NPN transistors  13 U,  13 V,  13 W,  14 U,  14 V and  14 W serving as switching elements and connected into a three-phase bridge configuration. Flywheel diodes  15 U,  15 V,  15 W,  16 U,  16 V and  16 W are connected across collectors and emitters of the transistors  13 U,  13 V,  13 W,  14 U,  14 V and  14 W respectively. Thus, the inverter circuit  12  has three arms  17 U,  17 V and  17 W. The inverter circuit  12  has input terminals  18  and  19  connected to DC bus bars  20  and  21  respectively. The inverter circuit  12  further has output terminals  22 U,  22 V and  22 W connected to respective one terminals of the stator coils  9 U,  9 v and  9 W of the brushless motor  9 . The stator coils  9 U,  9 V and  9 W have the respective other terminals connected together. The DC bus bar  21  is connected to a negative terminal of the battery  10 . A capacitor  23  is connected between the dc bus bars  20  and  21 .  
         [0020]    The control device  11  further includes a chopper circuit  24  comprising two NPN transistors  25  and  26  serving as switching elements and two diodes  27  and  28  connected across collectors and emitters of the transistors respectively. Three or more switching elements may be provided, instead. The collector of the transistor  25  is connected to the DC bus bar  20  and the emitter thereof is connected to the collector of transistor  26 . The emitter of the transistor  26  is connected to the DC bus bar  21 . A neutral point of the chopper circuit  24  is connected via a reactor  29  to a positive terminal of the battery  10 . The reactor  29  comprises a core and a coil wound on the core.  
         [0021]    The control device  11  further includes a battery voltage detector  30  connected in parallel with the battery  10  in order to detect a voltage across terminals of the battery. A main-circuit voltage detector  31  is connected in parallel with the capacitor  23  in order to detect a voltage across terminals of the capacitor  23  or main-circuit voltage. A position detector  32  is mounted in the brushless motor  9  and comprises Hall ICs (not shown) detecting a position of the rotor of the brushless motor  9 .  
         [0022]    The control device  11  further includes a microcomputer  33  serving as control means. The microcomputer  33  has input ports (not shown) to which output terminals of the battery voltage detector  30 , main-circuit voltage detector  31  and position detector  32  are connected respectively. The microcomputer  33  further has output terminals (not shown) connected to input terminals of photocoupler type base drive circuits  34  and  35  respectively. A control manner of the microcomputer  33  will be described later. The base drive circuit  34  has output terminals connected to the bases of the transistors  13 U,  13 V,  13 W,  14 U,  14 V and  14 W respectively. The base drive circuit  35  has output terminals connected to the bases of the transistors  25  and  26  of the chopper circuit  24 .  
         [0023]    The operation of the control device  11  will now be described. Firstly, the case where the brushless motor  9  serves as a starter for the engine  2  will be described. The microcomputer  33  renders the chopper circuit  24  non-operative when the detected voltage between the terminals of the battery  10  is at a rated value. As a result, the DC voltage of the battery is applied via the reactor  29  and the diode  27  to the capacitor  23  so that the capacitor is charged to a value suitable as an input voltage to the inverter circuit  12 . Further, the microcomputer  33  supplies a PWM signal to the base of the base drive circuit  35  when the voltage detected across the terminals of the battery  10  is lower than the rated value. As a result, a base signal is supplied to the negative transistor  26  of the chopper circuit  24 , so that the transistor  26  is turned on and off according to a duty of the PWM signal.  
         [0024]    Current from the battery  10  flows through the reactor  29  and the transistor  26  when the transistor  26  of the chopper circuit  24  is turned on. When the transistor  26  is turned off, electric energy stored in the reactor  29  is discharged via the diode  27  such that raised voltage is applied to the capacitor  23 . In this case, a step-up rate of the voltage depends upon the duty of PWM signal. The step-up rate becomes larger as the duty of PWM signal is increased. The microcomputer  33  determines the duty of PWM signal according to the voltage across the terminals of the battery  10 . As a result, the capacitor  23  is charged with electricity so that the voltage thereof is suitable for an input voltage of the inverter circuit  12 . Thus, the chopper circuit  24  and the reactor  29  serve as a step-up chopper at this time.  
         [0025]    When supplied with a starter signal, the microcomputer  33  generates an energization timing signal on the basis of a position signal delivered from the position detector  32 , applying the signal to the base drive circuit  34 . The base drive circuit  34  then delivers a base signal sequentially to the transistors  13 U to  13 W and  14 U to  14 W of the inverter circuit  12 , whereby the transistors are sequentially turned on and off. Consequently, an AC current flows into the brushless motor  9  or the stator coils  9 U to  9 W thereof mounted  120  electrical degrees apart, so that the rotor of the brushless motor  9  starts rotating. Upon starting of the brushless motor  9 , the output shaft of the engine  2  connected to the motor shaft is rotated, whereby the engine  2  starts. Accordingly, the brushless motor  9  serves as a starter for the engine  2  in this case.  
         [0026]    Secondly, the case where the brushless motor  9  serves as a generator will be described. Upon starting of the engine  2 , the microcomputer  33  stops delivery of base drive signals to the transistors  13 U to  13 W and  14 U to  14 W of the inverter circuit  12  so that all of these transistors are turned off, whereby the inverter circuit  12  is rendered non-operative. Upon starting of the engine  2 , the shaft of the brushless motor  9  or the rotor is rotated by the output shaft of the engine  2  so that voltage is induced in each of the stator coils  9 U to  9 W. The voltage induced in each stator coil is converted to DC voltage by each corresponding one of the flywheel diodes  15 U to  15 W and  16 U to  16 W of the inverter circuit  12  serving as a full-wave rectifier circuit. The brushless motor  9  thus serves as a generator in this case.  
         [0027]    The rotational speed of the output shaft of the engine  2  varies according to a degree of press against an accelerator (not shown) of the automobile  1 . Accordingly, the voltage induced in each of the stator coils  9 U to  9 W or generated voltage also varies according to the rotational speed of the output shaft of the engine  2  and the DC voltage applied to the capacitor  23  further varies accordingly. The microcomputer  33  controls the chopper circuit  24  so that the battery  10  is charged at a proper voltage. Firstly, the voltage across the terminals of the capacitor  23  or main circuit voltage is detected by the main-circuit voltage detector  31 . When the voltage detected by the main-circuit voltage detector  31  is higher than a rated voltage of the battery  10 , namely, the voltage generated by the brushless motor  9  is high, the microcomputer  33  delivers a PWM signal to the base drive circuit  35 . As a result, a base signal is applied to the base of the positive transistor  25  of the chopper circuit  24 , so that the transistor  25  is turned on and off according to the duty of the PWM signal. In this case, when the transistor  25  of the chopper circuit  24  is turned on, the voltage across the terminals of the capacitor  23  is applied via the reactor  29  to the battery  10  during an on time of the transistor  25 . Consequently, the voltage across the terminals of the capacitor  23  is stepped down and then applied to the battery  10 . In this case, a step-down rate of the voltage depends upon the duty of PWM signal. The step-down rate becomes larger as the duty of PWM signal is decreased. As a result, the battery  10  is charged with a proper voltage. Thus, the chopper circuit  24  and the reactor  29  serve as a step-down chopper in this case.  
         [0028]    On the other hand, when the voltage across the terminals of the capacitor  23  detected by the main-circuit voltage detector  31  is lower than the rated voltage of the battery  10 , namely, when the voltage generated by the brushless motor  9  is low, the microcomputer  33  renders the chopper circuit  24  non-operative. Accordingly, the transistors  25  and  26  are not turned on and off, or a repeated on-off operation of the transistors  25  and  26  is not carried out. In the embodiment, the transistor  25  is held in the on state. Further, the microcomputer  33  delivers the PWM signal to the base drive circuit  34  so that the base signal is supplied to the bases of the negative transistors  14 U to  14 W. As a result, the transistors  14 U to  14 W are turned on and off according to the duty of PWM signal. In this case, when the inverter circuit  12  is in a pattern that the current is caused to flow out from the stator coil  9 U of the brushless motor  9 , the transistor  14 U is turned on and off. The transistor  14 V is turned on and off when the inverter circuit  12  is in a pattern that the current is caused to flow out from the stator coil  9 V of the brushless motor  9 . The transistor  14 W is turned on and off when the inverter circuit  12  is in a pattern that the current is caused to flow out from the stator coil  9 W of the brushless motor  9 . When the transistor  14 U is turned on, the voltage induced in the stator coil  9 U,  9 V or  9 W causes a circulating current to flow through the stator coil  9 U, transistor  14  and flywheel diode  16 V or  16 W, and stator coil  9 V or  9 W. Consequently, electric energy is stored at the stator coil  9 U,  9 V or  9 W.  
         [0029]    When the transistor  14 U is turned off, the electric energy stored at the stator coils  9 U and  9 V or  9 W is discharged through the flywheel diode  15 U so that the raised voltage is applied to the capacitor  23 . In this case, a step-up rate of the voltage depends upon the duty of PWM signal. The step-up rate becomes larger as the duty of PWM signal is increased. The microcomputer  33  determines the duty of PWM signal according to the voltage across the terminals of the battery  10 . As a result, the capacitor  23  is charged with a voltage proper for charge of the battery  10 . Further, the principle of step-up by turning the transistors  14 V and  14 W on and off is the same as that by turning the transistor  14 U on and off described above. Accordingly, the inverter circuit  12  serves as a step-up chopper with the stator coils  9 U to  9 W as reactors.  
         [0030]    According to the foregoing embodiment, the shaft of the brushless motor  9  is directly connected to the output shaft of the engine  2  so that the brushless motor serves as the starter for the engine  2  at the time of starting of the engine. The brushless motor  9  is further driven by the engine  2  after starting of the latter so as to serve as the generator for charging the battery  10  with electricity. Accordingly, a single brushless motor  9  can serve as both starter for the engine  2  and generator for charging the battery  10 . Consequently, the mounting space of the automobile  1  can be reduced as compared with the conventional construction in which both starter and generator are individually provided. Moreover, since no clutch is required between the output shaft of the engine  2  and the shaft of the brushless motor  9 , the mounting space of the automobile  1  can further be reduced. When operated as the starter, the brushless motor  9  is driven by the inverter circuit  12  controlled by the microcomputer  33 . Consequently, no relay switch such as a conventional large starter relay is required between the battery  10  and the brushless motor  9 .  
         [0031]    Furthermore, when the voltage across the terminals of the battery  10  is at the rated voltage, the chopper circuit  24  is rendered non-operative and the capacitor  23  is recharged with the voltage across the terminals of the battery. When the voltage across the terminals of the battery  10  is lower than the rated voltage, the chopper circuit  24  and the reactor  29  are operated as the step-up chopper stepping up the voltage across the terminals of the battery  10  to thereby charge the capacitor  23  with the raised voltage.  
         [0032]    When the voltage generated by the brushless motor  9  operated as the generator is higher than the rated voltage of the battery  10 , the inverter circuit  12  is rendered non-operative and the chopper circuit  24  is operated as the step-down chopper to charge the battery  10  with electric energy. When the voltage generated by the brushless motor  9  is lower than the rated voltage of the battery  10 , the chopper circuit  24  is rendered non-operative though the positive transistor  25  is turned on, and the inverter circuit  12  is operated as the step-up chopper together with the stator coils  9 U to  9 W of the brushless motor  9 , so that the battery  10  is recharged.  
         [0033]    As the result of the above-described arrangement, even the brushless motor  9  having such a large torque as to be operable as a starter can sufficiently be operated as the generator to recharge the battery  10 . Further, even when the voltage of the battery  10  drops, the voltage can be stepped up such that the brushless motor  9  having the large torque can be started.  
         [0034]    FIGS.  3  to  5  illustrate a second embodiment of the invention. Only the differences between the first and second embodiments will now be described. In the second embodiment, the identical or similar parts are labeled by the same reference symbols as those in the first embodiment. Another chopper circuit  36  connected in parallel with the chopper circuit  24  is provided in the second embodiment. The second chopper circuit  36  includes two NPN transistors  37  and  38  serving as switching elements, and diodes  39  and  40 . The transistor  37  has a collector connected to the DC bus bar  20  and an emitter connected to a collector of the transistor  38 . The transistor  38  has an emitter connected to the DC bus bar  21 . The diodes  39  and  40  are connected between the collectors and emitters of transistors  37  and  38  respectively. Further, the second chopper circuit  36  has a neutral point connected via a reactor  41  to a positive terminal of the battery  10 . Accordingly, the second chopper circuit  36  is connected in parallel with the first chopper circuit  24 . Each of the reactors  29  and  41  includes one core and two coils wound on the core.  
         [0035]    The operation of the control device in the second embodiment will now be described with reference to FIGS.  3  to  5 . Firstly, when the chopper circuits  24  and  36  serve as step-up choppers, the microcomputer  33  drives the base drive circuit  35  which turns the transistors  26  and  38  on and off with a timing phase difference of 180 degrees. In this case, when the step-up rate is to be reduced, on times of the transistors  26  and  38  are rendered shorter than off times of the transistors respectively as shown in FIGS. 4A and 4B. On the other hand, when the step-up rate is to be increased, the on times of the transistors  26  and  38  are rendered longer than the off times of the transistors respectively as shown in FIGS. 5A and 5B.  
         [0036]    Further, when the chopper circuits  24  and  36  serve as step-down choppers, the microcomputer  33  drives the base drive circuit  35  which turns the transistors  25  and  37  on and off with a timing phase difference by 180 electrical degrees. In this case, when the step-down rate is to be increased, on times of the transistors  25  and  37  are rendered shorter than off times of the transistors respectively as shown in FIGS. 4A and 4B. On the other hand, when the step-down rate is to be reduced, the on times of the transistors  25  and  37  are rendered longer than the off times of the transistors respectively as shown in FIGS. 5A and 5B.  
         [0037]    According to the second embodiment, when the chopper circuits  24  and  36  are operated as the step-up choppers, the microcomputer  33  drives the base drive circuit  35  which turns the transistors  26  and  38  on and off with a timing phase difference by 180 electrical degrees. Consequently, DC power supply voltage with a smaller amount of ripple can be supplied to the capacitor  23 . Further, when the chopper circuits  24  and  36  serve as step-down choppers, the microcomputer  33  drives the base drive circuit  35  which turns the transistors  25  and  37  on and off with a timing phase difference by 180 electrical degrees. Consequently, when required to perform a high-speed switching as the step-down choppers, each of the transistors  25  and  37  is required to have only one half responsibility, whereby an amount of generated heat can be reduced. Further, when the transistors  25  and  37  are controlled so that the on times of the transistors are superposed on each other as shown in FIGS. 5A and 5B, the transistors  25  and  37  advantageously share the current.  
         [0038]    Although the second chopper circuit  36  includes the two transistors  37  and  38  in the second embodiment, a chopper circuit  42  in which the transistor  37  in the second embodiment is eliminated may be provided as shown as a third embodiment in FIG. 6, instead. In the third embodiment, only the transistor  25  of the chopper circuit  24  serves as the step-down transistor.  
         [0039]    The transistors  25  and  37  of the chopper circuits  24  and  36  may simultaneously be turned on and off in the case of step-down in the second embodiment. Further, although applied to the automobile in the embodiments, the present invention may be applied to all types of the motor vehicles provided with respective engines.  
         [0040]    The foregoing description and drawings are merely illustrative of the principles of the present invention and are not to be construed in a limiting sense. Various changes and modifications will become clear to those of ordinary skill in the art. All such changes and modifications are seen to fall within the scope of the invention as defined by the appended claims.