Abstract:
A method and system for controlling vehicle door position having reduced power supply current requirements reduces the cost and weight of a vehicle and further reduces power consumption. The vehicle door control system includes an inverter for converting a DC power source to an AC voltage for driving the motor. The inverter is preceded by a boost converter that maintains a constant voltage at the inverter input, and a capacitor is provided between the converter and inverter for energy storage. Kinetic energy is returned from the door and mechanical portions of the motor through the inverter and stored on the capacitor, reducing the power required from the power source. Operation of the inverter and converter are controlled by timers and detection mechanisms that cease operation of the inverter and converter when the door is held in a fully closed or open position for a predetermined interval.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally motor control systems, and more specifically to a vehicle door positioner power supply system that has a reduced power supply current requirement. 
     2. Background of the Invention 
     Automatic vehicle door opening and closing mechanisms are in widespread use in public transportation systems such as trains and buses, as well as in private vehicles adapted for use by the handicapped. The control of the operation of a vehicle door is typically performed by an electronic control system that determines the position and speed of a moving element of an electric motor that operates the door positioning mechanism. 
     An example of a conventional vehicle door apparatus is described in “Development of linear motor drive door system for commuter train”, Sato, et al., Papers delivered in the Convention held by the Industrial Application Section of The Institute of Electrical Engineers of Japan, 1999, The Institute of Electrical Engineers of Japan, 1999, at p. 359 to 362. In the above-referenced paper, the maximum output voltage of the inverter supplying power to the door motor is proportional to the power source voltage of the vehicle power distribution system. Therefore, when the power source voltage is lowered, the maximum voltage that can be supplied to the motor from the inverter is also lowered. Therefore, it is necessary to increase the rated current of the motor to obtain a given motor output when lower power supply voltages will be encountered. It is also necessary to increase the diameter of the wiring supplying power to the electric motor in order to avoid excessive voltage drop, adding cost and weight to the vehicle. 
     Therefore, it would be desirable to provide a vehicle door positioner power supply system that supplies the maximum output voltage of an inverter to a motor without being influenced by the fluctuation of the power source voltage, thereby reducing the cost and weight of the vehicle. It would further be desirable to provide a vehicle door positioner power supply system that reduces power consumption. 
     SUMMARY OF THE INVENTION 
     The above objectives of providing for reduced cost, weight and power consumption in a vehicle door positioning system is accomplished in a method and power supply system for a vehicle door positioner having reduced power supply current requirements. 
     The power supply system is connected to an electric motor that operates the vehicle door. An inverter supplies AC current to the electric motor and is preceded by a boost converter and capacitor that maintain a predetermined DC voltage at the input of the inverter. The inverter recovers the kinetic energy from the door and other positioning linkages back through the inverter and into capacitor, thereby reducing the overall power requirement of the system. The boost converter may be a current-reversible boost converter that returns power to the power source if the voltage on the capacitor is higher than the power supply voltage. 
     The boost converter maintains the voltage at the input of the inverter even when the power source voltage drops so that the current rating of the motor and associated wiring can be kept at a nominal level. The operation of the converter and inverter may be ceased in response to detecting that the position of the door is fixed, further improving the efficiency of the power supply system. 
     The method is a method of operation of the above-described power supply system and may be embodied therein. 
     The foregoing and other objectives, features, and advantages of the invention will be apparent from the following, more particular, description of the preferred embodiment of the invention, as illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram depicting a vehicle door control system in accordance with an embodiment of the invention. 
         FIG. 2  is a block diagram depicting a vehicle door control system in accordance with another embodiment of the invention. 
         FIG. 3  is a flowchart depicting a method in accordance with an embodiment of the invention. 
         FIG. 4  is a block diagram depicting details of the vehicle door control system of  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention is directed toward an electronic control system and method for controlling the position of a vehicle door. The control system operates an electric motor that opens/closes the vehicle door, which may be a public transportation vehicle door such as on a train or bus, or may be an automobile door. 
     Referring now to  FIG. 1 , a block diagram of a vehicle door control system in accordance with an embodiment of the invention is shown. A DC power source  1 , such as a battery, supplies power to a current reversible boost converter  2  that perform the DC-DC conversion of the DC power source  1  voltage to boost the voltage to a preset voltage level. A voltage detector  3  is coupled to the output of converter  2  to detect the converter output voltage and an electrolytic capacitor  4  is also coupled to the converter output to level the converter output voltage. The output of converter  2  is further coupled to a three-phase inverter  5  inverter that converts the DC voltage present on electrolytic capacitor  4  into an AC voltage and supplies the AC voltage to a motor  6  (shown as a linear motor) via wiring  5   a . Motor  6  drives a vehicle door  7  via a connection portion  8  that transmits a force from motor  6  to the door  7  and an encoder  9  which detects the position of the movable portion of the motor  6  and thus the position of door  7 . 
     A drive controller  10  controls converter  2  and inverter  5 . Drive controller  10  includes a door drive arithmetic unit  11  that sends an operate command to converter  2  and inverter  5  to move door  7  in response to a door open/close command. Drive controller  10  also includes a converter drive arithmetic unit  12  that performs computations for driving converter  2  in response to outputs from door drive arithmetic unit  11  and voltage detector  3 . Drive controller  10  further includes a position arithmetic unit  13  that computes the position of the movable portion of motor  6  and thereby door  7  from the output of the encoder  9 . Drive controller also includes an inverter drive arithmetic unit  14  for performing computations for operating the inverter  5  in response to outputs from door drive arithmetic unit  11 , voltage detector  3  and position arithmetic unit  13 . 
     When door  7  is moved from a closed position to a open position and stops at the open position, a door open command is provided to drive controller  10 . Door drive arithmetic unit  11  gives an operate command to converter drive arithmetic unit  12  and inverter drive arithmetic unit  14 . Converter drive arithmetic unit  12  operates the converter  2  in conformity with the output of the voltage detector  3  such that the voltage of the DC power source  1  is boosted to a desired voltage level. Further, inverter drive arithmetic unit  14  operates inverter  5  so that motor  6  is activated in the proper direction to change the position of door  7  to the open position as determined by the output of the position arithmetic unit  13 . 
     When inverter drive arithmetic unit  14  detects that the door  7  is in the vicinity of the opened position (as reflected by the output of position arithmetic unit  13 ), inverter drive arithmetic unit  14  controls inverter  5  to decelerate motor  6  in order to reduce the speed of door  7  in anticipation of stopping. Along with the deceleration of motor  6 , kinetic energy of door  7  (and the balance of the mechanical linkage including motor  6 ) is supplied to capacitor  4  through inverter  5 . This reduces the output requirements on DC power source, and if the voltage on capacitor  4  exceeds the voltage of DC power source  1 , current-reversible boost converter  2  returns power to DC power source  1 . 
     In general, when a linear motor is used as a driving force to open/close door  7 , it is possible move door  7  with a reduced the number of mechanical parts as compared to that required for a rotary-type motor. Therefore, the use of a linear motor results in reduced loss of energy during door opening and closing operations. When a rotary-type motor is used, the kinetic energy during door deceleration is substantially wholly consumed as loss in the door positioning mechanisms. In contrast, when a linear motor is used, since the loss in the mechanism is small, the electric power produced by the kinetic energy at the time of deceleration can be returned to the power source. 
     Further, due to the presence of booster converter  2 , it is possible to supply a substantially fixed DC voltage to inverter  5  uninfluenced by voltage fluctuations of DC power source  1 . Therefore, the maximum output voltage of inverter  5  can always be supplied to motor  6 , so that the rated voltage of motor  6  can be increased and the rated current for obtaining a given motor rated output can be reduced. Also, the size of wiring  5   a  can be reduced and therefore the cost and weight of wires, resulting in a reduction in the weight of the vehicle. 
     Referring now to  FIG. 2 , a vehicle door control system in accordance with another embodiment of the invention is shown. Common elements of  FIG. 2  are numbered with the same reference designator as elements in  FIG. 1  and operate as described above. Therefore only differences between the embodiment of  FIG. 2  and the embodiment of  FIG. 1  will be described hereinafter below. In the embodiment of  FIG. 2 , a terminal position of door (fully closed or fully open) can be detected and the operation of converter  2  and inverter  5  can be ceased, resulting in power savings. Further, a timer within door controller  10 A can be used to delay ceasing the operation of converter  2  until a predetermined time period has elapsed after ceasing operation of inverter  5   
     In the embodiment of  FIG. 2 , a locking device  15  is provided to mechanically and automatically lock door  7  in a closed position and further provides an output to drive controller  10 A. Also, a door closed position detector  16  that detects when the door  7  is in the fully closed state is additionally provided in the vicinity of the door  7  and is coupled to drive controller  10 A. 
     With reference now to  FIG. 3 , operation of door drive arithmetic unit  11  in the embodiment of  FIG. 2  is depicted in a flowchart. When a door close command is provide to drive control  10  and door  7  is in the fully closed state, outputs are received from both of locking device  15  and door closed position detector  16  (S 1  Yes, S 2  Yes). When a door open command is received (S 1  No), if door drive arithmetic unit  11  determines that door  7  is not at the fully opened position (S 14  No), if converter  2  is off (S 19  Yes), converter drive arithmetic unit  12  turns on the converter  2  and at the same time clears an OFF timer (S 19  to S 21 ). When the output voltage of converter  2  reaches a reference value necessary for operating inverter  5  (S 22  Yes), if inverter  5  is off (S 23  Yes) inverter drive arithmetic unit  14  turns on inverter  5  (S 24 ). Door  7  is then opened (S 25 ). 
     When door  7  reaches the fully opened position (S 14  Yes), inverter  5  is stopped (S 15 ), and converter  2  is turned off (S 17 ) after an OFF timer value lapses a second set time (S 16  Yes). In order to immediately open door  7  when in the closing direction due to the inclination of a vehicle, tampering or the like when door  7  is fully open, the second set time can be extended so that converter  2  continues to run after the inverter  5  is stopped. When the OFF timer value does not reach the second set time, the OFF timer value is incremented and the control cycle is finished (S 18 ). 
     When a door close command is received (S 1  Yes) and there are no outputs from both the locking device  15  and the door closed position detector  16 , it is determined that the door is not in the fully closed state (S 2  No). Therefore, if converter  2  is off (S 7  Yes), converter drive arithmetic unit  12  turns on converter  2  (S 8 ) to commence boosting. Next, the OFF timer is cleared (S 9 ). 
     When the output voltage of converter  2  reaches the reference value necessary for operating the inverter  5  (S 10  Yes), if inverter  5  is off (S 11  Yes), inverter drive arithmetic unit  14  turns on inverter  5  to drive the motor  6 , thus closing door  7  (S 13 ). Upon detection of outputs from both locking device  15  and door closed position detector  16 , it is determined that the door is in the fully closed state (S 2  Yes). In response to determining that door  7  is fully closed, inverter drive arithmetic unit  14  turns off inverter  5  (S 3 ) and converter  2  is also stopped (S 5 ) after a lapse of the first set time (S 4  Yes). When the OFF timer value does not reach the first set time, the OFF timer value is incremented (S 6 ) and the control cycle is finished. 
     In the above-described manner, according to the illustrated embodiment, when a door open or close operation is not in progress, operation of the inverter  5  and the converter  2  is ceased (S 2  Yes, S 3  to S 5  and S 14  Yes, S 15  to S 17 ), thus power consumption is reduced. 
     Referring now to  FIG. 4 , details of the vehicle door control systems of  FIGS. 1 and 2  are shown in a block diagram. Current-reversible boost converter  20  receives a DC input voltage Vin and switches current through inductor L 1 . Transistors Q 1  and Q 2  perform switching in response to signals from a converter control circuit  22  to provide a DC voltage on capacitor  4 . Voltage detector  3  is shown and provides an output to drive control  10 ,  10 A as described above. Three-phase inverter  24  provides three AC output voltage phases (commonly labeled Vout) via switching of the voltage stored on capacitor  4  through transistors Q 3 – 5  and Q 6 – 8  in response to signals provided from an inverter control circuit  26 . When the voltage at any phase of Vout exceeds that of capacitor  4  as will occur during deceleration of door  7 , capacitor  4  will be charged through three-phase inverter  24 . Motor  6  is then acting as a generator recovering kinetic energy from door  7  and moving parts of motor  6 . The energy returned to capacitor  4  reduces the power required from boost converter  20 , as converter  20  operates to maintain a uniform voltage, thus reducing overall power consumption. If the voltage across capacitor  4  exceeds Vin, then the current through boost converter  20  flows into the DC power source, returning power to the power source. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form, and details may be made therein without departing from the spirit and scope of the invention. 
     The application incorporates by reference the entire disclosures of applicants&#39; corresponding Japanese patent application no. 2003-297535, filed Aug. 21, 2003, and Japanese patent application no. 2004-061066535, filed Mar. 4, 2004.