Abstract:
A combined drive circuit for a split brake system of a motor vehicle has a switched reluctance motor and a brush motor. The switched reluctance motor has multiple phase windings. The combined drive circuit includes a DC power source with first and second supply buses. A SR motor driver supplies current to the switched reluctance motor. The SR motor driver has a first capacitor coupled to the phase windings for storing energy from the phase windings and a second capacitor coupled to the first capacitor and a third supply bus, thereby developing a third supply bus voltage across the second capacitor. A brush motor driver is coupled to the first and second capacitor. The SR motor driver is adapted to supply current to the brush motor. The brush motor driver includes first, second, third and fourth switching elements coupled to the brush motor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/170,558, filed Dec. 14, 1999. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to electric motors and, more particularly, to a combined driver circuit for a brush motor and a switched reluctance motor.  
           [0004]    2. Background of the Invention  
           [0005]    Electric motors are used in a variety of applications. Two types of electric motors are brush motors and switched reluctance motors. Each has different operating characteristics and therefore, advantages suitable for different applications.  
           [0006]    For example, a split brake system for a motor vehicle typically controls a front and diagonally opposed rear brake. The front brake requires high response performance and the rear brake requires significantly reduced response performance. Thus, a brush motor is used to actuate the rear brake and a switched reluctance motor is used to actuate the front brake.  
           [0007]    With regard to the switched reluctance motor, the drive circuit is comprised of power switching devices and diodes for sequentially energizing the motor phase windings in accordance with the position of the rotor to produce a rotating magnetic field that interacts with the rotor poles to produce torque of a desired direction and magnitude.  
           [0008]    A number of drive circuit topologies have been proposed to minimize the number of power devices in an effort to reduce the cost of the driver circuit. One such topology is described in U.S. Pat. No. 4,835,408 issued to Ray et al. The circuit disclosed in Ray, commonly referred to as a split-link circuit, utilizes capacitors to establish an intermediate voltage bus. One or more of the phase windings are coupled to the intermediate voltage bus. In automobile applications, the supply voltage is typically 12 volts. Such a design reduces the number of power devices required, but only one half of the supply voltage is available for energizing the phase windings. As a result, the efficiency of the drive is reduced due to increased switching and conduction losses.  
           [0009]    U.S. Pat. No. 5,900,712 issued to Disser et al, maintains a second bus at a voltage which is either higher or lower than the supply voltage, thereby extending the voltage range of the supply.  
           [0010]    With regard to the brush motor, motor direction is controlled by the polarity of the voltage applied to the brush terminals. Since it is desirable to maximize power to the brake, it is desirable to apply full supply voltage to the brush terminals.  
           [0011]    The present invention is aimed at one or more of the problems above.  
         BRIEF SUMMARY OF THE INVENTION  
         [0012]    In one aspect of the present invention, a combined drive circuit for a switched reluctance motor and a brush motor is provided. The switched reluctance motor has multiple phase windings. The combined drive circuit includes a DC power source with first and second supply buses. A SR motor driver supplies current to the switched reluctance motor. The SR motor driver has a first capacitor coupled to the first and second supply buses for storing energy from the DC power source and a second capacitor coupled to the first capacitor and a third supply bus, thereby developing a third supply bus voltage across the second capacitor. A brush motor driver is coupled to the first and second capacitor. The SR motor driver is adapted to supply current to the brush motor. The brush motor driver has first, second, third and fourth switching elements coupled to the brush motor.  
           [0013]    In another aspect of the present invention, a combined drive circuit for a split brake system of a motor vehicle is provided. The split brake system has a switched reluctance motor and a brush motor. The switched reluctance motor has multiple phase windings. The combined drive circuit includes a DC power source with first and second supply buses. A SR motor driver supplies current to the switched reluctance motor. The SR motor driver has a first capacitor coupled to the first and second supply buses for storing energy from the DC power source and a second capacitor coupled to the first capacitor and a third supply bus, thereby developing a third supply bus voltage across the second capacitor. A brush motor driver is coupled to the first and second capacitor. The SR motor driver is adapted to supply current to the brush motor. The brush motor driver has first, second, third and fourth switching elements coupled to the brush motor. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a block diagram of a combined drive circuit for a brush motor and a switched reluctance motor;  
         [0015]    [0015]FIG. 2 is a schematic of the combined drive circuit of FIG. 1, according to an embodiment of the present invention;  
         [0016]    [0016]FIG. 3 is a block diagram illustrating connections between the combined drive circuit and the brush motor of FIG. 1; and,  
         [0017]    [0017]FIG. 4 is a block diagram illustrating connections between the combined drive circuit and the switched reluctance motor of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    With reference to FIGS. 1 and 2, the present invention provides a combined drive circuit  102  for a switched reluctance (SR) motor  104  and a brush motor  106 . The switched reluctance motor  104  includes multiple phase windings (see below). A DC power source  116  supplies power to the combined drive circuit  102 . The combined drive circuit  102  includes a brush motor driver  108  and a switched reluctance (SR) motor driver  110 . First and second controllers  112 ,  114  apply control signals to the brush and SR drivers  108 ,  110  to control the current supplied to the respective motor  106 ,  104 . In the preferred embodiment, the control signals are pulse width modulated (PWM) signals. The generation of such PWM signals and the control of brush motors and SR motors are well known in the art, and thus, is not further discussed.  
         [0019]    A DC power supply  116  supplies power to the brush motor  106  and the SR motor  104  through the respective driver  108 ,  110 . The DC power supply  116 , which may be a battery, such as a conventional automotive storage battery, or a source of rectified AC, is connected to the combined driver circuit  102  at first and second supply terminals  118 A,  118 B.  
         [0020]    With reference to FIG. 2, the first supply terminal  118 A defines a first supply bus  202  and the second supply terminal  118 B defines a second supply bus  204 . The combined driver circuit  102  includes a third supply bus  206 , as described below.  
         [0021]    With reference to FIGS. 3 and 4, the combined driver circuit  102  includes first and second terminals, T 1 , T 2 . The brush motor  104  is coupled to the combined driver circuit  102  at the first and second terminals, T 1 , T 2 . The combined driver circuit  102  also includes third, fourth, fifth, sixth, seventh and eighth terminals, T 3 , T 4 , T 5 , T 6 , T 7 , T 8 . The first controller  112  includes ninth, tenth, eleventh, twelfth, thirteenth, and fourteenth terminals T 9 , T 10 , T 11 , T 12 , T 13 , T 14 . The combined driver circuit  102  is coupled to the first controller  112  via the third through fourteenth terminals, T 3 , T 4 , T 5 , T 6 , T 7 , T 8 , T 9 , T 10 , T 11 , T 12 , T 13 , T 14 , as shown.  
         [0022]    The combined driver circuit  102  also includes fifteenth, sixteenth, seventeenth, eighteenth, nineteenth, and twentieth terminals, T 15 , T 16 , T 17 , T 18 , T 19 , T 20 . The SR motor  104  preferably includes first, second, third, and fourth phase windings  402 A,  402 C,  402 B,  402 D. The first phase winding  402 A is connected at a first end of the fifteenth terminal T 15  and at a second end to the twentieth terminal T 20 . The second phase winding  402 B is connected at a first end to the seventeenth terminal T 17  and at a second end to the nineteenth terminal T 19 . The third phase winding  402 C is connected at a first end to the sixteenth terminal T 16  and at a second end to the twentieth terminal T 20 . The fourth phase winding  402 D is connected at a first end to the eighteenth terminal T 18  and at a second end to the nineteenth terminal T 19 .  
         [0023]    The combined circuit driver  102  also includes twenty-first, twenty-second, twenty-third, twenty-fourth, twenty-fifth, and twenty-sixth terminals, T 21 , T 22 , T 23 , T 24 , T 25 , T 26 . The second controller  114  includes twenty-seventh, twenty-eighth, twenty-ninth, thirtieth, thirty-first, thirty-second, thirty-third and thirty-fourth terminals, T 27 , T 28 , T 29 , T 30 , T 31 , T 32 , T 33 , T 34 . The combined driver circuit  102  is coupled to the second controller  114  via the twenty-first through thirty-fourth terminals, T 21 , T 22 , T 23 , T 24 , T 25 , T 26 , T 27 , T 28 , T 29 , T 30 , T 31 , T 32 , T 33 , T 34 , and the sixteenth and eighteenth terminals T 16 , T 18 , as shown.  
         [0024]    Returning to FIG. 2, the SR motor driver  110  includes a first capacitor  208  and a second capacitor  210 . The second capacitor  210  is coupled to the first capacitor  208  and the third supply bus  206 . The second capacitor  210  is also coupled to the phase windings  402 A,  402 B,  402 C,  402 D, developing a third supply bus (B++ or times the battery voltage of B+). The SR motor driver  110  includes first, second, third, fourth, fifth and sixth power transistors  212 ,  214 ,  216 ,  218 ,  220 ,  222  and first and second free-wheeling diodes  224 ,  226 .  
         [0025]    The first and second power transistors and the first and second free-wheeling diodes  224 ,  226 ,  212 ,  214 , direct inductive currents stored in the respective phase windings  402 A,  402 B,  402 C,  402 D to one of the capacitors  208 ,  210 , or to another of the phase windings  402 A,  402 B,  402 C,  402 D being energized.  
         [0026]    The twentieth terminal T 20  is coupled to the first supply bus  202  by a first resistor  228 . The nineteenth terminal T 19  is coupled to the first supply bus  202  by a second resistor  230 . The sixteenth and twenty-third terminals T 16 , T 23  are coupled to the first power transistor  212  by a third capacitor  232  and a third resistor  234 , respectively. The eighteenth and twenty-fifth terminals T 18 , T 25  are coupled to the second power transistor  214  by a fourth capacitor  236  and a fourth resistor  238 , respectively.  
         [0027]    The twenty-first terminal T 21  is coupled to the third power transistor  216  by a fifth resistor  240 . The twenty-second terminal T 22  is coupled to the fourth power transistor  218  by a sixth resistor  242 . The twenty-fourth terminal T 24  is coupled to the fourth power transistor  220  by a seventh resistor  244 . The twenty-sixth terminal T 26  is coupled to the sixth power transistor  222  by a eighth resistor  246 .  
         [0028]    The second controller  114  generates a pulse-width modulated (PWM) signal in order to control the SR motor  104  via the SR motor driver  110 . Such a system is disclosed in U.S. Pat. No. 5,900,712 issued May 4, 1999 to Robert J. Disser, et al (Disser), which is hereby incorporated by reference. While the SR motor driver  110  described above generates a supply voltage above the DC power supply voltage  116 , the driver  110  could be adapted to generate a supply voltage having a negative magnitude of B−. Such a circuit is also described in Disser. Other embodiment of the SR motor driver  110  are disclosed in Disser, all of which fall under the scope of the present invention.  
         [0029]    The brush motor driver  108  is coupled to the SR motor driver  110 . By providing a third supply bus  206 , the brush motor  106  can be driven by the increased voltage resulting in improved free speed and thus, better response rate.  
         [0030]    The brush motor driver  108  is coupled to the first and second capacitor  208 ,  210  of the SR motor driver  110 . The brush motor driver  110  is adapted to supply current to the brush motor  106 . The brush motor driver  110  includes first, second, third and fourth switching elements or power FET transistors  248 ,  250 ,  252 ,  254  coupled to the brush motor  106 . Preferably, the first, second, third, and fourth switching elements are connected in an “H” configuration as shown. The first switching element  248  is coupled to the third terminal T 3  by a ninth resistor  256  and to the fourth terminal T 4  by a fifth capacitor  258 . The second switching element  250  is coupled to the fifth terminal T 5  by a tenth resistor  260  and to the sixth terminal T 6  by a sixth capacitor  262 . The third switching element  252  is coupled to the seventh terminal T 7  by an eleventh resistor  264  and to the second supply bus  204  by a seventh capacitor  266  and a twelfth resistor  268 . The fourth switching element  254  is coupled to the eighth terminal T 8  by a thirteenth resistor  270  and to the second supply bus  204  by an eighth capacitor  272  and the twelfth resistor  268 .  
         [0031]    The first controller  112  uses conventional PWM control techniques to control both motor current and motor voltage to achieve desired motor performance.  
         [0032]    The brush motor  106  operates between ground (the second supply bus  204 ) and the third power supply voltage , B++. The increased voltage improves the free speed and thus the response rate of the brush motor  104 .  
         [0033]    With this invention has been described in reference to the illustrated embodiment, it will be understood that various modifications and design variations will occur to those skilled in the art, and that drive circuits and controls incorporating such modifications may fall within the scope of this invention, which is defined by the appended claims.